Category: Biology

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Viruses – Definition | Structure | Various Types of Viruses and its Function

Did you go through the headlines of newspapers in recent times? Have you heard of the terms EBOLA, ZIKA, AIDS, SARS, H1N1 etc.? There are serious entities which are considered as “Biological Puzzle” and cause disease in man. They are called viruses. We have learnt about the attributes of living world in the previous chapter. Now we shall discuss about viruses which connect the living and nonliving world.

The word virus is derived from Latin meaning ‘Poison’. Viruses are submicroscopic, obligate intracellular parasites. They have nucleic acid core surrounded by protein coat. Viruses in their native state contain only a single type of nucleic acid which may be either DNA or RNA. The study of viruses is called Virology.

Milestones in Virology

• 1796 – Edward Jenner used vaccination for small pox
• 1886 – Adolf Mayer demonstrated the infectious nature of Tobacco mosaic virus using sap of mosaic leaves
• 1892 – Dimitry Ivanowsky proved that viruses are smaller than bacteria
• 1898 – M.W. Beijierink defined the infectious agent in tobacco leaves as ‘Contagium vivum fluidum’
• 1915 – F.W.T wort identified Viral infection in Bacteria
• 1917 – d’Herelle coined the term ‘Bacteriophage’
• 1984 – Luc Montagnier and Robert Gallo discovered HIV (Human Immuno Deficiency Virus).

Size and Shape

Viruses are ultramicroscopic particles. They are smaller than bacteria and their diameter range from 20 to 300 nm. (1nm = 10^-9 metres). Bacteriophage measures about 10-100 nm in size. The size of TMV is 300×20 nm.

Generally viruses are of three types based on shape and symmetry (Figure 1.4).

• Cuboid Symmetry – Example: Adenovirus, Herpes virus.
• Helical Symmetry – Example: Influenza virus, TMV.
• Complex or Atypical – Example: Bacteriophage, Vaccinia virus.

Characteristic Features of Viruses

Living Characters

• Presence of nucleic acid and protein
• Capable of mutation
• Ability to multiply within living cells
• Able to infect and cause diseases in living beings
• Show irritability
• Host – specific

Non-living Characters

• Can be crystallized
• Absence of metabolism
• Inactive outside the host
• Do not show functional autonomy
• Energy producing enzyme system is absent

Classification of Viruses

Among various classifications proposed for viruses the classification given by David Baltimore in the year 1971 is given below. The classification is based on mechanism of RNA production, the nature of the genome (single stranded – ss or double stranded – ds), RNA or DNA, the use of reverse transcriptase (RT), ss RNA may be (+) sense or (–) antisense. Viruses are classified into seven classes (Table 1.2).

Viral Genome

Each virus possesses only one type of nucleic acid either DNA or RNA. The nucleic acid may be in a linear or circular form. Generally nucleic acid is present as a single unit but in wound tumour virus and in influenza virus it is found in segments. The viruses possessing DNA are called ‘Deoxyviruses’ whereas those possessing RNA are called ‘Riboviruses’.

Majority of animal and bacterial viruses are DNA viruses (HIV is the animal virus which possess RNA). Plant viruses generally contain RNA (Cauliflower Mosaic virus possess DNA). The nucleic acids may be single stranded or double stranded. On the basis of nature of nucleic acid viruses are classified into four Categories. They are Viruses with ssDNA (Parvo viruses), dsDNA (Bacteriophages), ssRNA (TMV) and dsRNA(Wound Tumour Virus).

Tobacco Mosaic Virus (TMV)

Tobacco mosaic virus was discovered in 1892 by Dimitry Ivanowsky from the Tobacco plant. Viruses infect healthy plants through vectors like aphids, locusts etc. The first visible symptom of TMV is discoloration of leaf colour along the veins and show typical yellow and green mottling which is the mosaic symptom. The downward curling and distortion of young apical leaves occurs, plant becomes stunted and yield is affected.

Structure

Electron microscopic studies have revealed that TMV is a rod shaped (Figure 1.4b) helical virus measuring about 300x20nm with a molecular weight of 39×10⁶ Daltons. The virion is made up of two constituents, a protein coat called capsid and a core called nucleic acid.

The protein coat is made up of approximately 2130 identical protein subunits called capsomeres which are present around a central single stranded RNA molecule. The genetic information necessary for the formation of a complete TMV particle is contained in its RNA. The RNA consists of 6,500 nucleotides.

Bacteriophage

Viruses infecting bacteria are called Bacteriophages. It literally means ‘eaters of bacteria’ (Gr: Phagein = to eat). Phages are abundant in soil, sewage water, fruits, vegetables, and milk.

Structure of T₄ Bacteriophage

The T₄ phage is tadpole shaped and consists of head, collar, tail, base plate and fibres (Figure 1.4). The head is hexagonal which consists of about 2000 identical protein subunits. The long helical tail consists of an inner tubular core which is connected to the head by a collar.

There is a base plate attached to the end of tail. The base plate contains six spikes and tail fibres. These fibres are used to attach the phage on the cell wall of bacterial host during replication. A dsDNA molecule of about 50 µm is tightly packed inside the head. The DNA is about 1000 times longer than the phage itself.

Multiplication or Life Cycle of Phages

Phages multiply through two different types of life cycle. a. Lytic or Virulent cycle b. Lysogenic or Avirulent life cycle.

a. Lytic Cycle

During lytic cycle of phage, disintegration of host bacterial cell occurs and the progeny virions are released (Figure 1.5 a). The steps involved in the lytic cycle are as follows:

(i) Adsorption

Phage (T₄) particles interact with cell wall of host (E. coli). The phage tail makes contact between the two, and tail fibres recognize the specific receptor sites present on bacterial cell surface. The lipopolysaccharides of tail fibres act as receptor in phages.

The process involving the recognition of phage to bacterium is called landing. Once the contact is established between tail fibres and bacterial cell, tail fibres bend to anchor the pins and base plate to the cell surface. This step is called pinning.

(ii) Penetration

The penetration process involves mechanical and enzymatic digestion of the cell wall of the host. At the recognition site phage digests certain cell wall structure by viral enzyme (lysozyme). After pinning the tail sheath contracts (using ATP) and appears shorter and thicker.

After contraction of the base plate enlarges through which DNA is injected into the cell wall without using metabolic energy. The step involving injection of DNA particle alone into the bacterial cell is called Transfection. The empty protein coat leaving outside the cell is known as ‘ghost’.

(iii) Synthesis

This step involves the degradation of bacterial chromosome, protein synthesis and DNA replication. The phage nucleic acid takes over the host biosynthetic machinery. Host DNA gets inactivated and breaks down. Phage DNA suppresses the synthesis of bacterial protein and directs the metabolism of the cell to synthesis the proteins of the phage particles and simultaneously replication of Phage DNA also takes place.

(iv) Assembly and Maturation

The DNA of the phage and protein coat are synthesized separately and are assembled to form phage particles. The process of assembling the phage particles is known as maturation. After 20 minutes of infection, about 300 new phages are assembled.

(v) Release

The phage particle gets accumulated inside the host cell and are released by the lysis of host cell wall.

b. Lysogenic Cycle

In the lysogenic cycle the phage DNA gets integrated into host DNA and gets multiplied along with nucleic acid of the host. No independent viral particle is formed (Figure 1.5 b).

As soon as the phage injects its linear DNA into the host cell, it becomes circular and integrates into the bacterial chromosome by recombination. The integrated phage DNA is now called prophage. The activity of the prophage gene is repressed by two repressor proteins which are synthesized by phage genes. This checks the synthesis of new phages within the host cell. However, each time the bacterial cell divides, the prophage multiplies along with the bacterial chromosome.

On exposure to UV radiation and chemicals the excision of phage DNA may occur and results in lytic cycle. Virion is an intact infective virus particle which is non-replicating outside a host cell.

Viroid is a circular molecule of ssRNA without a capsid and was discovered by T.O.Diener in the year 1971. The RNA of viroid has low molecular weight. Viroids cause citrus exocortis and potato spindle tuber disease in plants.

Virusoids were discovered by J.W.Randles and Co-workers in 1981. They are the small circular RNAs which are similar to viroids but they are always linked with larger molecules of the viral RNA.

Prions were discovered by Stanley B. Prusiner in the year 1982 and are proteinaceous infectious particles. They are the causative agents for about a dozen fatal degenerative disorders of the central nervous system of humans and other animals. For example Creutzfeldt – Jakob Disease (CJD), Bovine Spongiform Encephalopathy (BSE) – commonly known as mad cow disease and scrapie disease of sheep.

Viral Diseases

Viruses are known to cause disease in plants, animals and Human beings (Figure 1.6). A list of viral disease is given in Table 1.3.

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Attributes of Living Organisms

The attributes of living organisms are given below and is represented in Figure 1.1.

Growth

Growth is an intrinsic property of all living organisms through which they can increase cells both in number and mass. Unicellular and multicellular organisms grow by cell division. In plants, growth is indefinite and occurs throughout their life. In animals, growth is definite and occurs for some period. Growth in non-living objects is extrinsic.

Mountains, boulders and sand mounds grow by simple aggregation of material on the surface. Living cells grow by the addition of new protoplasm within the cells. Therefore, growth in living thing is intrinsic. In unicellular organisms like Bacteria and Amoeba growth occurs by cell division and such cell division also leads to the growth of their population. Hence, growth and reproduction are mutually inclusive events.

Cellular Structure

All living organisms are made up of cells which may be prokaryotic or eukaryotic. Prokaryotes are unicellular, lack membrane bound nuclei and organelles like mitochondria, endoplasmic reticulum, golgi bodies and so on (Example: Bacteria and Blue green algae). In Eukaryotes a definite nucleus and membrane bound organelles are present. Eukaryotes may be unicellular (Amoeba) or multicellular (Oedogonium).

Reproduction

Reproduction is one of the fundamental characteristic features of living organisms. It is the tendency of a living organism to perpetuate its own species. There are two types of reproduction namely asexual and sexual (Figure 1.2).

Asexual reproduction refers to the production of the progeny possessing features more or less similar to those of parents. The sexual reproduction brings out variation through recombination. Asexual reproduction in living organisms occurs by the production of conidia (Aspergillus, Penicillium), budding (Hydra and Yeast), binary fission (Bacteria and Amoeba) fragmentation (Spirogyra), protonema (Mosses) and regeneration (Planaria). Exceptions are the sterile worker bees and mules.

Response to Stimuli

All organisms are capable of sensing their environment and respond to various physical, chemical and biological stimuli. Animals sense their surroundings by sense organs. This is called Consciousness. Plants also respond to the stimuli. Bending of plants towards sunlight, the closure of leaves in touch-me-not plant to touch are some examples for response to stimuli in plants. This type of response is called Irritability.

Homeostasis

Property of self-regulation and tendency to maintain a steady state within an external environment which is liable to change is called Homeostasis. It is essential for the living organism to maintain internal condition to survive in the environment.

Metabolism

The sum of all the chemical reactions taking place in a cell of living organism is called metabolism. It is broadly divided into anabolism and catabolism. The difference between anabolism and catabolism is given in Table 1.1.

Movement, Nutrition, Respiration and Excretion are also considered as the property of living things. The levels of organization in living organism begin with atoms and end in Biosphere. Each level cannot exist in isolation instead they form levels of integration as given in Figure 1.3.

Activity 1.1

Collect Vallisneria leaves or Chara from nearby aquarium and observe a leaf or Chara thallus (internodal region) under the microscope. You could see cells clearly under the microscope. Could you notice the movement of cytoplasm? The movement of cytoplasm is called cytoplasmic streaming or cyclosis.

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Animal Husbandary and Management

Animal husbandry is the practice of breeding and raising livestock cattles like cows, buffloes, and goats and birds etcthat are useful to human beings. Parameters such as adequate ventilation, temperature, sufficient light, water and proper housing accommodation should be taken into account to maintain dairy and poultry farms.

Animals should be cared and protected from diseases. Records should be maintained after the regular visits by Veterinarian. More over the selection of good breeds with high yielding potential combined and resistance to diseases is very important.

Animal Breeding

Human beings have been depending on animals and animal products for food from very early times. Generally high yielding animals produced by hybridization are reared in poultry and dairy farms. In earlier days, animals were produced and selected based on specific characters.

With the gain in knowledge on the principles of heredity and genetics, human beings have been successful in rearing animals with the superior qualities through hybridization experiments. Complex issues are faced by the animal breeder during hybridization experiments.

Hence animals with maximum desirable characters should be selected. A group of animals related by descent and with similar characters like general appearance, features, size etc., are said to belong to a breed. Why should we breed animals? Through animal breeding, improved breeds of animals can be produced by improving their genotype through selective breeding.

Objectives of Animal Breeding:

• To improve growth rate
• Enhancing the production of milk, meat. Egg etc.,
• Increasing the quality of the animal products
• Improved resistance to diseases
• Increased reproductive rate

Methods of Animal Breeding:

There are two methods of animal breeding, namely inbreeding and outbreeding

1. In Breeding:

Breeding between animals of the same breed for 4-6 generations is called inbreeding. Inbreeding increases homozygosity and exposes the harmful recessive genes. Continuous inbreeding reduces fertility and even productivity, resulting in “inbreeding depression”.

This can be avoided by breeding selected animals of the breeding population and they should be mated with superior animals of the same breed but unrelated to the breeding population. It helps to restore fertility and yield.

2. Out Breeding:

The breeding between unrelated animals is called outbreeding. Individuals produced do not have common ancestors for 4-6 generations. Outbreeding helps to produce new and favourable traits, to produce hybrids with superior qualities and helps to create new breeds. New and favourable genes can be introduced into a population through outbreeding.

(i) Out Crossing:

It is the breeding between unrelated animals of the same breed but having no common ancestry. The offspring of such a cross is called outcross. This method is suitable for breeding animals below average in productivity.

(ii) Cross Breeding:

Breeding between a superior male of one breed with a superior female of another breed. The cross bred progeny has superior traits (hybrid vigour or heterosis).

(iii) Interspecific Hybridization:

In this method of breeding mating is between male and female of two different species. The progeny obtained from such crosses are different from their parents, and may possess the desirable traits of the parents. Have you heard about Mule? It was produced by the process of interspecific hybridization between a male donkey and a female horse.

Controlled Breeding Experiments Artificial Insemination:

Artificial insemination is a technique in which the semen collected from the male is injected to the reproductive tract of the selected female. Artificial insemination is economical measure where fewer bulls are required and maximum use can be made of the best sire.

Advantages of Artificial Insemination

• It increases the rate of conception
• It avoids genital diseases
• Semen can be collected from injured bulls which have desirable traits
• Superior animals located apart can be bred successfully

Multiple Ovulation Embryo Transfer Technology (MOET)

It is another method of propagation of animals with desirable traits. This method is applied when the success rate of crossing is low even after artificial insemination. In this method Follicle stimulating hormone (FSH) is administered to cows for inducing follicular maturation and super ovulation. Instead of one egg per cycle, 6-8 eggs can be produced by this technology. The eggs are carefully recovered non-surgically from the genetic mother and fertilized artificially.

The embryos at 8-32 celled stages are recovered and transferred to a surrogate mother. For another round of ovulation, the same genetic mother is utilized. This technology can be applied to cattle, sheep and buffaloes. Advantage of this technology is to produce high milk yielding females and high-quality meat yielding bulls in a short time.

Breeds of Dairy Animals

Dairying is the production and marketing of milk and its products. Dairy operation consists of proper maintenance of cattle, the collection and processing the milk and its by products. There are 26 well defined breeds of cattle and 6 breeds of buffaloes in India. Cattles are classified under three groups based on the purpose they serve to man (Figure 12.12). They are:-

(i) Dairy Breeds or Milch Breeds:

They are high milk yielders with extended lactation. Eg., Sindhi, Gir, Sahiwal, Jersy, Brown Swiss, Holstein cattle.

(ii) Draught Purpose Breeds:

Bullocks are good for draught purpose. Eg. Kangayam, Malvi

(iii) Dual Purpose Breeds:

Cows are meant for yielding more milk and bullocks are used for better drought purpose. Eg. Ongole, Hariana

To meet the milk demand of the growing population, milk breeds are preferred by farmers in small scale farms. Goats are also used all over India for supplementing deficiencies in milk production. Some of the breeds of cattle that are good milkers are Jamunapari in Ganga-Jamuna riverine tracts, Beetal in Punjab, Bar-bari in Uttarpradesh.

Common Diseases of Cattle:

A healthy animal eat, drinks and sleeps well regularly. Healthy cattle appear bright, alert and active in their movement with a shiny coat. Cattle are affected by a large number of diseases. Cattle in ill health appear dull, restless and change posture frequently with drop in milk yield. The main diseases of dairy cattle are rinderpest, foot and mouth disease, cow pox, hemorrhagic fever, anthrax.

Uses of Dairy Products:

Milk Products:

Milk is produced by dairy animals which is an emulsion of fat and lactose. Milk also contains enzymes which are destroyed during pasteurization. Milk is a rich source of vitamin A, B₁, B₂, and deficient in Vitamin C. Due to its high nutrition value, it serves as a complete food for infants. Dairy products such as yoghurt, cheese, butter, ice cream, condensed milk, curd, and milk powder processed from milk make dairy, a highly farming attraction.

Meat:

Meat is rich in protein and also contains many minerals like iron, zinc, vitamins and selenium. It also contains vitamins needed for human diet.

Land Management:

Grazing of livestock is sometimes used as a way to control weeds and undergrowth.

Manure:

Manure can be spread on agriculture fields to increase crop yields.

Poultry Farming:

The word poultry refers to the rearing and propagation of avian species such as chicken, ducks, turkeys, geese, quail and guinea fowls. The most common and commercially farmed birds are chicken and ducks. Poultry farming is essential for the purpose of meat, eggs and feather production. Commercial poultry farming is also profiable. In this part we are discussing about an overview of the chicken and duck breeds, farming practices and its advantages.

Types of Chicken Breeds:

There are more than 100 breeds. The commonly farmed chicken breeds are categorized into five based on the purpose for which it is farmed. They are egg layers, broiler type, dual type, games and ornamental types (Figure 12.13).

1. Egg Layers:

These are farmed mainly for the production of egg.

Leghorn:

This is the most popular commercial breed in India and originated from Italy. They are small, compact with a single comb and wattles with white, brown or black colour. They mature early and begin to lay eggs at the age of 5 or 6 months. Hence these are preferred in commercial farms. They can also thrive well in dry areas.

Chittagong:

It is the breed chiefly found in West Bengal. They are golden or light yellow coloured. The beak is long and yellow in colour. Ear lobes and wattles are small and red in colour. They are good egg layers and are delicious.

2. Broiler Type:

These are well known for fast growth and soft quality meat.

White Plymouth Rock:

They have white plumage throughout the body. It is commonly used in broiler production. This is an American breed. It is a fast growing breed and well suitable for growing intensively in confined farms.

3. Dual Purpose Breeds:

These are for both meat and egg production purpose.

Brahma:

It is a breed popularly known for its massive body having heavy bones, well feathered and proportionate body. Pea comb is one of the important breed characters. It has two common varieties namely, Light Brahma and Dark Brahma.

4. Game Breeds:

Since ancient times, special breed of roosters have been used for the sport of cockfighting.

Aseel:

This breed is white or black in colour. The hens are not good egg layers but are good in incubation of eggs. It is found in all states of India. Aseel is noted for its pugnacity, high stamina, and majestic gait and dogged fighting qualities. Although poor in productivity, this breed is wellknown for their meat qualities.

5. Ornamental Breeds:

Ornamental chicken are reared as pets in addition to their use for egg production and meat.

Silkie:

It is a breed of chicken has a typical fluffy plumage, which is said to feel like silk and satin. The breed has numerous additional special characters, such as black skin and bones, blue earlobes, and fie toes on each foot, while the majority chickens only have four.

They are exhibited in poultry shows, and come out in various colours. Silkies are well recognized for their calm, friendly temperament. Silkie chicken is especially simple to maintain as pets.

Types of Poultry Farming:

There are different methods used to rear both broiler and layer chicken. The types of poultry farming are free range farming, Organic method, Yarding method, Battery cage method and Furnished cage method.

Among these, Battery cage method is widely used in large scale poultry farms. The Free range, Organic and Yarding methods are eco-friendly and the eggs produced by such farming practices are preferred in the market.

Stages Involved in Rearing:

There are some steps involved in rearing of chicken.

Selection of the Best Layer:

An active intelligent looking bird, with a bright comb, not obese should be selected.

Selection of Eggs for Hatching:

Eggs should be selected very carefully. Eggs should be fertile, medium sized, dark brown shelled and freshly laid eggs are preferred for rearing. Eggs should be washed, cleaned and dried.

Incubation and Hatching:

The maintenance of newly laid eggs in optimum condition till hatching is called incubation. The fully developed chick emerges out of egg after an incubation period of 21 – 22 days. There are two types of incubation namely natural incubation and artificial incubation.

In the natural incubation method, only a limited number of eggs can be incubated by a mother hen. In artificial incubation, more number of eggs can be incubated in a chamber (Incubator).

Brooding:

Caring and management of young chicks for 4 – 6 weeks immediately after hatching is called brooding. It can also be categorized into two types namely natural and artificial brooding.

Housing of Poultry:

To protect the poultry from sun, rain and predators it is necessary to provide housing to poultry. Poultry house should be moisture – proof, rat proof and it should be easily cleanable and durable.

Poultry Feeding:

The diet of chicks should contain adequate amount of water, carbohydrates, proteins, fats, vitamins and minerals.

Poultry Products:

The main products of poultry farming are eggs and meat. In India, the primary aim of poultry farming is to obtain eggs. The eggs and poultry meat are the richest sources of proteins and vitamins.

Poultry By Products:

The feathers of poultry birds are used for making pillows and quilts. Droppings of poultry can be used as manure in fields. The droppings are rich in nitrogen, potash and phosphates.

A number of poultry byproducts like blood-meal, feather meal, poultry byproduct meal and hatchery by product meal are used as good sources of nutrients for meat producing animals and poultry. These byproducts supply proteins, fats, vitamins and good amount of minerals.

Poultry Diseases:

Ranikhet, Coccidiosis, and Fowl pox are some common poultry diseases.

Benefits of Poultry Farming:

The advantages of poultry farming are:-

• It does not require high capital for construction and maintenance of the poultry farming.
• It does not require a big space.
• It ensures high return of investment within a very short period of time.
• It provides fresh and nutritious food and has a huge global demand.
• It provides employment opportunities for the people.

Duck Farming

Duck is an aquatic bird and forms only 6% of our country’s poultry population. There are about 20 breeds of ducks. The native one includes Indian Runner and Syhlet meta. The exotic breeds include Muscori, Pekin, Aylesbury and Campbell. Domesticated ducks have been derived from the wild duck named Mallard (Anas boscas). Farming ducks is profiable as it can be combined with aquafarming practices.

Peculiarity of Ducks:

The body is fully covered with oily feathers. They have a layer of fat under their skin which prevents it from getting wet. They lay eggs at night or in the morning. The ducks feed on rice bran, kitchen wastes, waste fish and snails.

Types of Breeds:

There are three types of ducks depending on the purpose for which it is formed. They are meat productive duck breeds, egg productive duck breeds, and breeds for both meat and egg production.

Advantages of Duck Farming:

They can be reared in small backyards where water is available and needs less care and management as they are very hardy. They can adapt themselves to all types of environmental conditions and are breed for feed efficiency, growth rate and resistance to diseases.

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Aquaculture and its Various Types of Culture

Aquaculture has been practiced in varying forms for centuries dating to the time of the Phoenicians. India offers a huge potential for aquaculture development. Fish culture received notable attention in Tamil Nadu in 1911. Aquaculture is a branch of science that deals with the farming of aquatic organisms such as fish, molluscs, crustaceans and aquatic plants.

On the basis of source, aquaculture can be classified into three categories. They are:

• Freshwater Aquaculture
• Brackish Water Aquaculture
• Marine water aquaculture.

Culturing of fishes is called fish culture or pisciculture. Inland water bodies include freshwater bodies like rivers, canals, streams, lakes, flood plain wetlands, reservoirs, ponds, tanks and other derelict water bodies and ponds constructed for fresh water aquaculture. The pH of the freshwater should be around neutral and salinity below 5 ppt (parts per thousand).

Brackish water fishes spend most of its life in river mouths (estuaries) back waters, mangrove swamps and coastal lagoons. Estuarine fish are more common in Bengal and Kerala. Culturing of animals in the water having salinity range 0.5 – 30 ppt are called as brackish water culture. Fishes cultured in brackish water are Milk fish (Chanos Chanos), Sea bass (‘Koduva’), Grey mullet (‘Madavai’), Pearl spots (‘Kari’meen) etc,

Marine Fisheries deal with fishing operations along seacoasts. The Indian subcontinent approximately has a 5600 kms long coastline. About 80% of India’s marine fish are supplied by the west coast and the remaining 20% by the east coast. The premier varieties are mackerels, sardines, sharks, and catfish. Marine edible fishes of tamilnadu coast include both cartilaginous and bony fishes.

Culturing of animals in the water salinity ranges from 30 – 35 ppt is called Mariculture. Some fishes like Chanos sp, Mugil cephalus are cultured here. Culturing of animals in the salinity ranges from 36 – 40 ppt is called Metahaline culture. Eg, Brine shrimp (Artemia salina). Artemia is commonly known as the brine shrimp. It is a crustacean and lives in high saline waters because of its high osmoregulatory capacity.

Fish Culture

Characteristics of Cultivable Fishes

The Special Characteristic Features of Cultivable Fishes are:

• Fishes should have high growth rate in short period for culture.
• They should accept supplementary diet.
• They should be hardy enough to resist some common diseases and infection of parasites.
• Fishes proposed for polyculture should be able to live together without interfering or attacking other fishes.
• They should have high conversion efficiency so that they can effectively utilize the food.

Types of Cultivable Fish

Cultivable fish are of 3 types (Figure 12.8).

• Indigenous or native fresh water fishes (Major carps, Catla, Labeo, Clarias)
• Salt water fihes acclimatized for fresh water (Chanos, Mullet).
• Exotic fihes or imported from other counties (Common carps)

Among these, major carps have proved to be best suited for culture in India, because the carps

• Feed on zooplavnktons and phytoplanktons, decaying weeds, debris and other aquatic plants.
• They can survive in turbid water with slightly higher temperature
• Can tolerate O₂ variations in water.
• Can be transported from one place to other easily.
• They are highly nutritive and palatable.

External Factors Affecting Fish Culture

The factors that affect fish culture are temperature, light, rain, water, flood, water current, turbidity of water, pH hardness, salinity and dissolved O₂. Light and temperature also play an important role in fish breeding.

Management of Fish Farm

To culture fish, one should have an idea about different stages of fish culture such as topographic situation, quality, source, physical, chemical and biological factors of water. Breeding, hatching, nursing, rearing and stocking fishes in ponds has to be managed properly. Keeping in view the various stages of fishes, the following different types of ponds have been recommended to manage them.

Breeding Pond

The first step in fish culture is the breeding of fishes, therefore, for proper breeding special types of ponds are prepared called breeding ponds. These ponds are prepared near the rivers or other natural water resources.

Types of Breeding

Depending on the mode of breeding, they are divided into

1. Natural Breeding (Bundh Breeding)

These are special types of ponds where natural riverine conditions or any natural water resources are managed for breeding of culturable fishes. There bundhs are constructed in large low-lying areas that can accommodate large quantity of rain water. The shallow area of such bundhs is used as spawning ground.

2. Induced Breeding

The fish seed is commonly collected from breeding grounds but does not guarantee that all fish seeds belong to the same species. Hence advanced techniques have been developed to improve the quality of fish seed by artificial method of fertilization and induced breeding. Artificial fertilization involves removal of ova and sperm from female and male by artificial mechanical process and the eggs are fertilized.

For artificial fertilization the belly of mature female fish is held upward. Stripping is done with the thumb of the right hand from the anterior to posterior direction for the ejection of eggs due to force. In this way eggs are collected separately. Further, the male fish is caught with its belly downwards. The milt of fish is stripped and collected separately, and then the eggs are fertilized.

Induced breeding is also done by hypophysation (removal of pituitary gland). The gonadotropin hormone (FSH and LH) secreted by the pituitary gland influences the maturation of gonads and spawning in fishes. Pituitary gland is removed from a healthy mature fish. Pituitary extract is prepared by homogenising in 0.3% saline or glycerine and centrifuged for 15 minutes at 8000rpm.

The supernatant is injected intramuscularly at the base of the caudal fin or intra-peritonealy at the base of pectoral fin. Male and female fishes start to spawn (release of gametes) and eggs are fertilized. The fertilized eggs are removed from the spawning place and kept into hatching hapas.

Fish Seed

Fish seed is collected from breeding ponds. The spawn collecting net is commonly called Benchijal (Shooting net) and transferred to the hatching pits.

Hatching Pit

The fertilized eggs are kept in hatching pits. The hatching pits should be nearer to the breeding grounds, should be smaller in size with good quality water. There are two types of hatching pits, hatcheries are small sized pond in which unfertilized eggs are transferred and hatching happens.

Hatching hapas are rectangular trough shaped tanks made up of mosquito net cloth supported by bamboo poles and fixed in the river (Figure 12.9).

Nursery Pond

The newly hatched fries are transported from the hatching happa to nursery ponds where they grow into fingerlings.

Rearing Pond

Fingerlings are transferred to rearing ponds that is long and narrow and allows long distance swimming. The rearing pond should be free from toxicants and predators. Antibiotics are used for washing the fingerlings and then transferred to the stocking ponds.

Stocking Ponds

Stocking ponds should be devoid of weeds and predatory fishes. Proper organic manuring should be done to increase the production with cow dung and chemical fertilizing should also be done.

Harvesting

Harvesting is done to capture the fishes from the water. Well grown fishes are taken out for marketing. Small sized fishes are again released into the stocking ponds for further growth. Different methods of fishing are carried out to harvest fishes.

These include Stranding, Angling, Traps, Dipnets, Cast nets, Gill nets, Drag nets and purse nets. The harvested fishes are preserved by refrigeration, Deep freezing, freeze drying, sun drying, salting, smoking and canning.

Composite Fish Farming

Few selected fishes belonging to different species are stocked together in proper proportion in a pond. This mixed farming is termed composite fish farming or polyculture. The advantages include,

• All available niches are fully utilized.
• Compatible species do not harm each other.
• No competition among different species is found.
• Catla catla, Labeo rohita and Cirrhinus mrigala are the commonly used fish species for composite fish farming.

Exotic Fishes

The fishes imported into a country for fish culture are called exotic fishes and such fish culture is known as exotic fish culture. Examples of such exotic fishes introduced in India are Cyprinus carpio and Oreochromis mossambicus.

Disease Management

Diseases can be of viral or bacterial origin. Regular monitoring of parameters like water quality, aeration, regular feeding, observation for mortality should be checked. Parasitic infestations and microbial infections should be observed periodically.

Economic Importance of Fish

Fishes frrm a rich source of protein food and provide a good staple food to tide over the nutritional needs of man. Fish species such as sardines, mackerel, tuna, herrings have high amino acids concentrations particularly histidine which is responsible for the meaty flavour of the flesh. It is rich in fat such as omega 3 fatty acids. Minerals such as calcium, magnesium, phosphorus, potassium, iron, manganese, iodine and copper. Some of the fish by – products are;

Fish Oil

Is the most important fish by product. It is derived from fish liver and from the fish body. Fish liver oil is derived from the liver which is rich in vitamin A and D, whereas fish body oil has high content of iodine, not suitable for human consumption, but is used in the manufacture of laundry soaps, paints and cosmetics.

Fish Meal

Is prepared from fish waste after extracting oil from the fish. The dried wastes are used to prepare food for pig, poultry and cattle. The wastes obtained during the preparation of fish meal are widely used as manure.

Isinglass

Is a high-grade collagen produced from dried air bladder or swim bladder of certain fishes viz. catfish and carps. The processed bladder which is dissolved in hot water forms a gelatin having adhesive property. It is primarily used for clarification of wine, beer and vinegar.

Prawn Culture

Most important aquatic crustacean is prawn, which is widely cultured prawn flesh is palatable and rich in glycogen, protein with low fat content.

Types of Prawn Fishery

1. Shallow Water Prawn Fishery:

Located on the west coast restricted to shallow waters.

2. Estuaries and Back Waters or Saline Lake Prawn Fishery:

The area of production of prawns are the back waters seen along the Western coast, Ennur, Pulicat, Chilka lake and Estuaries of Ganga and Brahmaputra rivers.

3. Freshwater Prawn Fishery:

Prawns are caught from the rivers and lakes throughout India.

4. Marine Prawn Fishery:

Most of the marine prawns are caught along the Indian coast belonging to the family Penaeidae.

Species of Prawn

A number of species of prawn are distributed in water resources such as Penaeus indicus, Penaeus monodon, Metapenaeus dobsoni and Macrobrachium rosenbergii.

Culture of Freshwater Prawn

Macrobrachium rosenbergii (Figure 12.10) is commonly seen in rivers, paddy fields and lowsaline estuaries. The prawn collected from ponds, river, and paddy fields are transferred to the tanks which are aerated. For fertilization, one pair of prawn are kept in a separate tank. After mating, the eggs are laid.

Spawning tanks of different sizes should be prepared with proper aeration. Temperature (24° C – 30° C) and pH (7-8) should be maintained in the hatching tank. The eggs hatch into first and second stage larva. Artificial feed is supplied. Young ones of 5cm length (60 days old) can be reared in fresh or slightly brackish water ponds and paddy fields. Harvesting of prawns can be done twice in a year.

Culture of Marine Prawn

Several factors that determine the success of marine prawn culture includes selection of site, water quality, soil quality and availability of seed.

Preparation of Farm

For the preparation of ponds for algal growth and for the subsequent stocking of prawns it is essential to drain off the water and sundry the bottom followed by light tilling. Agricultural lime should be applied to absorb excess CO₂ and to supply calcium which is required for moulting.

Fertilizers like rice, bran, poultry, and cattle dung are used to increase the fertility of the soil. Prawns are commonly caught in crafts and gears using different types of nets such as cast nets, bag nets, drag nets, trawl nets and barrier nets. Preservation of prawns is done by peeling and deveining or by cooking and peeling.

Pearl Culture

Pearl is a white, highly shining globular concretion found within the shell of an Oyster. Pearl oysters are sedentary animals. In India it was cultured for the first time in 1973 at Thothukudi. Pearl oysters are found along the coast of Kanyakumari and in the Gulf of Kutch.

High quality pearls are obtained from pearl oysters of Genus Pinctada that can be cultured in the salinity range of 30 ppt in racks, raf and long line methods. Freshwater bivalve Lamellidens is also used in artificial pearl culture. Mostly the pearl oysters inhabit the ridges of rocks or dead corals, forming extensive pearl banks. These pearl beds produce best quality of pearls called as “Lingha Pearl”.

Pearl Formation

When a foreign particle accidently enters into the space between mantle and shell of the oyster, it adheres to the mantle. The mantle epithelium encloses it like a sac and starts to secrete concentric layers of nacre around it as a defensive mechanism.

Nacre is secreted continuously by the epithelial layer of the mantle and is deposited around the foreign particle and over a period time the formation of repeated layers of calcium carbonate makes the hard and glossy pearl. When the pearl enlarges the oyster dies. The shell is then carefully opened and the pearls are manually separated and graded (Figure 12.11).

Composition of Pearl

Pearl comprises of water, organic matter, calcium carbonate and the residue.

(1) Water:
2-4%

(2) Organic Matter:
3.5-5.9%

(3) Calcium Carbonate:
90%

(4) Residue:
0.1-0.8%

Quality of Pearl

The pearls obtained are of variable shapes and sizes. They may be white, or cream red or pink red in colour. The spherical pearls of rainbow colour are rarely found. The best quality of pearl is obtained from marine oysters. Pearl obtained from freshwater bivalves are not as valuable as those obtained from the marine oysters (Mishra, 1961).

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Aquaponics and its Advantages

Aquaponics is a technique which is a combination of aquaculture (growing fish) and hydroponics (growing plants in non-soil media and nutrient-laden water). Aquaponics may also prevent toxic water runoff. It also maintains ecosystem balance by recycling the waste and excretory products produced by the fish. In India, aquaponics was started in 2013. Some primary methods of aquaponic gardening that are in use nowadays are as follows:

(i) Deep Water Culture

Is otherwise known as raft based method. In this method a raft flats in water. Plants are kept in the holes of raft and the roots flat in water. This method is applicable for larger commercial scale system. By this method fast growing plants are cultivated.

(ii) Media Based

Method involves growing plants in inert planting media like clay pellets or shales. This method is applicable for home and hobby scale system. Larger number of fruiting plants, leafy green plants, herbs and other varieties of plants can be cultivated (Figure 12. 7)

(iii) Nutrient Film Technique

Involves the passage of nutrient rich water through a narrow trough or PVC pipe. Plants are kept in the holes of the pipe to allow the roots to be in free contact with in the water stream.

(iv) Aqua Vertica 

Is otherwise known as vertical aquaponics. Plants are stacked on the top of each other in tower systems. Water flows in through the top of the tower. This method is suitable for growing leafy greens, strawberries and other crops that do not need supporting solid substratum to grow.

Advantages of Aquaponic Gardening

Water Conservation:

No need of water discharge and recharge as the water is maintained by recycling process.

Soil:

Bottom soil may be loaded with freshwater. Microbes in water can convert the waste materials into usable forms like ammonia into nitrates which are used by the plants. Thus the soil fertility is maintained.

Pesticides:

In this system use of pesticides is avoided and hence it is ecofriendly.

Weeds:

Since the plants are cultured in confined conditions, growth of weeds is completely absent. The utilization of nutrient by plants is high in this method.

Artificial Food for Fishes:

In this system plant waste and decays are utilized by fishes as food. So, the need for the use of supplementary feed can be minimized.

Fertilizer Usage:

Artificial or chemical fertilizers is not required for this system since the plants in the aquaponics utilize the nutrients from the fish wastes dissolved in water.

Cultivable fishes like tilapia, trout, koi, gold fish, bass etc., are cultured in aquaponics. Common cultivable plants like tomato, pepper, lettuce, cucumber, and rose are co-cultivated in this method.

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Lac Culture and its Importance

The culture of lac insect using techniques for the procurement of lac on large scale is known as Lac culture. Lac is produced by the lac insect Tachardia lacca previously known as Laccifer lacca. It is a minute, resinous crawling scale insect which inserts its probosics into the plant tissues and sucks juice, grows and secretes lac from the hind end of the body as a protective covering for its body.

Moreover the insect is a parasite on host plants i.e., Karanagalli (Acacia catechu), Karuvelai (Acacia nilotica) and Kumbadiri (Schleichera oleosa). The quality of lac depends upon the quality of the host plant. The female lac insect is responsible for large scale production of lac, which is larger than the male lac insect.

Economic Importance of Lac

• Lac is largely used as a sealing wax and adhesive for optical instruments. It is used in electric industry, as it is a good insulator.
• It is used in preparations of shoe and leather polishes and as a protective coating of wood.
• It is used in laminating paper board, photographs, engraved materials and plastic moulded articles.
• Used as a filing material for gold ornaments.

Lac is a natural resin of animal origin. It is secreted by an insect, known as lac-insect in order to obtain lac, these insects are cultured and the technique is called lac-culture. It involves proper care of host plants, regular pruning of host plants, propagation, collection and processing of lac.

Lac is used in ammunition, airplanes, furniture polish and perfumes, and in making bangles, imitation fruits and flowers. The ‘scientists’ motive was to give lac farmers a host plant that grows faster and reduces tree based farming. Ninety per cent of lac is produced on palash, ber and kusum trees.

Lac cultivation has its roots in India and Bangladesh, the two main Asian countries in the world and was a major source of economy to the local populace. Natural red color obtained on purification of this resin was used in coloring of items like wood and textiles.

Lac is a thick semi-solid gummy substance acquired from a female insect (bug) named ‘Tachardia lacca’ on trees in the forests of India and Thailand. The process of making Lac jewelry is complex and requires high degree of precision.

Lac is actually secreted for protection by females. It generally infests about 400 plant species and feed on the host tissues. The females are degenerated in form and feeds on the sap of its host plants. Male undergoes complete metamorphosis while female undergoes degeneration.

Lac is a natural resin secreted by the tiny insects, mainly K. lacca. The insects are cultured on tender shoots of several plants called hosts. However in costal region of West Bengal and Odisha, a tri-voltine insect, Kerria sharda is found which produce three crops in a year.

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Apiculture Methods Definition and Its Structure

Ever since the beginning of civilization, man has been trying to make use of organisms around him for various purposes and to rear them for increasing their number. One of the finest discoveries is our knowledge regarding the procurement of honey collected by honey bees. Care and management of honey bees on a commercial scale for the production of honey is called Apiculture or Bee Keeping.

The word ‘apiculture’ comes from the Latin word ’apis’ meaning bee. Bees are reared in apiaries that are areas where a lot of bee hives can be placed. There are fie well recognized types of bees in the world. They are Apis dorsata (Rock bee), Apis florea (Little bee), Apis indica (Indian bee), Apis mellifera (European bee) and Apis adamsoni (African bee).

Social Organization of Honey Bees

In honey bees, a highly organized division of labour is found. A well developed honey bee colony consists of the Queen, Drones and Workers (Figure 12.4). All the three types depend on each other for their existence. There is normally one queen, 10,000 to 30,000 workers and few hundred drones (male bees) in a colony.

Queen bee is a functional female bee present in each hive and feeds on Royal Jelly. Its sole function is to lay eggs throughout its life span. The virgin queen bee mates only once in her life. During the breeding season in winter, a unique flight takes place by the queen bee followed by several drones. This flight is called “nuptial flight”. The queen bee produces a hormonal chemical substance called pheromone.

The drones in the area are attracted to the pheromone and mating takes place. During mating, the drone releases large number of sperms for sufficient fertilization. In a life span of two to four years, a queen bee lays about 15 lakh eggs. When the queen bee loses its capacity to lay eggs, another worker bee starts feeding on the Royal Jelly and develops into a new queen.

Among the honey bees, workers are sterile females and smallest but yet function as the main spring of the complicated machinery in the colony. Worker bee lives in a chamber called ‘Worker Cell’ and it takes about 21 days to develop from the egg to adult and its lifespan is about six weeks.

Each worker has to perform different types of work in her life time. During the first half of her life, she becomes a nurse bee attending to indoor duties such as secretion of royal jelly, prepares bee-bread to feed the larvae, feeds the queen, takes care of the queen and drones, secretes bees wax, builds combs, cleans and fans the bee hive.

Then she becomes a soldier and guards the bee hive. In the second half her life lasting for three weeks, she searches and gathers the pollen, nectar, propolis and water.

The drone is the functional male member of the colony which develops from an unfertilized egg. It lives in a chamber called drone cell. Drones totally depend on workers for honey. The sole duty of the drone is to fertilize the virgin queen hence called “King of the colony”. During swarming (the process of leaving the colony by the queen with a large group of worker bees to form a new colony) the drones follows the queen, copulates and dies after copulation.

Structure of a Bee Hive

The house of honey bee is termed as bee hive or comb. The hive consists of hexagonal cells made up of wax secreted by the abdomen of worker bees arranged in opposite rows on a common base. These hives are found hanging vertically from the rocks, building or branches of trees.

The young stages of honey bees accommodate the lower and central cells of the hive called the brood cells. In Apis dorsata, the brood cells are of similar in size and shape but in other species, brood cells are of three types viz., queen cell for queens, worker cell for workers and drone cells for drones (Figure.12.5). The cells are intended for storage of honey and pollen in the upper portion of the comb whereas the lower portions are for brood rearing.

Methods of Bee Keeping

The main objective is to get more and more quality honey. There are two methods used by apiculturists. They are indigenous method and the modern method. In indigenous method, the honey extracted from the comb contains wax.

To overcome the drawbacks of the indigenous method, the modern method has been developed to improve the texture of hives. In India, there are two types of beehives in practice namely, Langstroth and Newton.

The Langstroth bee hive is made up of wood and consists of six parts (Figure 12.6) namely Stand, Bottom board, Brood chamber, Super, Inner cover and Top cover. Besides the above primary equipments, other accessory equipments are used in beekeeping. They are Queen Excluder, Comb foundation, Bee gloves, Bee veil, Smoker, Hive Tool, Uncapping knife, Bee brush, Queen introducing cage, Feeder, Honey Extractor and Hive Entrance Guard.

Products of Bee Keeping and Their Economic Importance

The chief products of bee keeping industry are honey and bee wax. Honey is the healthier substitute for sugar. The major constituents of honey are: levulose, dextrose, maltose, other sugars, enzymes, pigments, ash and water.

It is an aromatic sweet material derived from nectar of plants. It is a natural food, the smell and taste depends upon the pollen taken by the honey bee. It is used as an antiseptic, laxative and as a sedative. It is generally used in Ayurvedic and Unani systems of medicine.

It is also used in the preparation of cakes, breads and biscuits Bee wax is secreted by the abdomen of the worker bees at the age of two weeks. The wax is masticated and mixed with the secretions of the cephalic glands to convert it into a plastic resinous substance.

The resinous chemical substance present in the wax is called propolis which is derived from pollen grains. The pure wax is white in colour and the yellow colour is due to the presence of carotenoid pigments. It is used for making candles, water proofing materials, polishes for floors, furniture, appliances, leather and taps. It is also used for the production of comb foundation sheets in bee keeping and used in pharmaceutical industries.

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Sericulture – Diseases and Pests of Silkworm

Silk is Nature’s gift to mankind and a commercial fiber of animal origin other than wool. Being eco-friendly, biodegradable and self-sustaining material; silk has assumed special relevance in present age. Sericulture is an agro – based industry, the term which denotes commercial production of silk through silkworm rearing. Historical evidence reveals that sericulture was practiced in China long back and they preserved the secret for more than 3000 years and maintained monopoly in silk trade with the rest of the world.

According to Western historians, mulberry cultivation spread to India about 140BC from China through Tibet. The fabulous silk from China and India were carried to European countries. The 7000 mile lengthy road, historically called the “Silk road” passing through Baghdad, Tashkent, Damascus and Istanbul was used for silk transport. Today more than 29 countries in the world are practicing sericulture and producing different kinds of silk. India stands second in silk production next to China.

Production of silk from the silk worm, by rearing practices on a commercial scale is called sericulture. It is an agrobased industry comprising three main components:

• Cultivation of food plants for the silkworms
• Rearing of silkworms, and
• Reeling and spinning of silk.

The first two are agricultural and the last one is an industrail component. Only few species of silkworms are used in the sericulture industry (Table 12.1 and Figure 12.2).
Table 12.1: Different Types of Silkworm

Life Cycle of Bombyx Mori

The adult of Bombyx mori is about 2.5 cm in length and pale creamy white in colour. Due to heavy body and feeble wings, flight is not possible by the female moth. This moth is unisexual in nature and does not feed during its very short life period of 2-3 days. Just after emergence, male moth copulates with female for about 2-3 hours and if not separated, they may die after few hours of copulating with female.

Just after copulation, female starts egg laying which is completed in 1-24 hours. A single female moth lays 400 to 500 eggs depending upon the climatic conditions. Two types of eggs are generally found namely diapause type and non-diapause type.

The diapause type is laid by silkworms inhabiting the temperate regions, whereas silkworms belonging to subtropical regions like India lay non-diapause type of eggs. The eggs after ten days of incubation hatch into larva called about 3 mm in length and is pale, yellowishwhite in colour. The caterpillars are provided with well developed mandibulate type of mouth-parts adapted to feed easily on the mulberry leaves.

After 1^st, 2^nd, 3^rd and 4^th moultings caterpillars get transformed into 2^nd, 3^rd, 4^th and 5^th instars respectively (Figure 12.3). It takes about 21 to 25 days after hatching. The fully grown caterpillar is 7.5 cm in length.

It develops salivary glands, stops feeding and undergoes pupation. The caterpillars stop feeding and move towards the corner among the leaves and secretes a sticky fluid through their silk gland. The secreted fluid comes out through spinneret (a narrow pore situated on the hypopharynx) and takes the form of long fie thread of silk which hardens on exposure to air and is wrapped around the body of caterpillar in the forms of a covering called as cocoon.

It is the white coloured bed of the pupa whose outer threads are irregular while the inner threads are regular. The length of continuous thread secreted by a caterpillar for the formation of cocoon is about 1000-1200 metres which requires 3 days to complete. The pupal period lasts for 10 to 12 days and the pupae cut through the cocoon and emerge into adult moth.

On the basis of the moults which they undergo during their larval life, B. mori is divided into three races – tri-moulters, tetramoulters and pentamoulters. Based on voltinism (the number of broods raised per year), three kinds of races are recognized in mulberry silkworm – univoltines (one brood only), bivoltines (two broods only) and multivoltines (more than two broods).

Cultivation of Food Plants for the Silkworms

The first component, is to grow the food plants for the silkworms. Mulberry leaves are widely used as food for silkworm Bombyx mori and the cultivation of mulberry is called as Moriculture. Presently improved mulberry varieties like Victory1, S36, G2 and G4 which can withstand various agro – climatic and soil conditions are used for planting.

The favourable season for cultivating of the mulberry plants is June, July, November and December. The mulberry crop production technology includes land preparation, preparation of cutting, planting techniques, maintenance of mulberry nursery, disease and pest management and uprooting for raising new mulberry gardens. Mulberry is also being grown as tree plant at an height of 123-152 cm with 20 x 20 cm or 25 x 25 cm spacing to harvest better silkworm cocoon crops.

Rearing of Silkworms

The second component is the rearing of silkworm. A typical rearing house (6m x 4m x 3.5m) is constructed on an elevated place under shade to accommodate 100 dfls (disease free layings). Space of 1m should be provided surrounding the rearing house. Sufficient windows and ventilators should be provided for free circulation of air inside the rearing house.

The windows and ventilators should be covered with nylon net to restrict the entry of uzi flies and other insects. Apart from the specified area of the rearing house; the following appliances such as hygrometer, power sprayers, rearing stands, foam pads, wax coated paraffin papers, nylon nets, baskets for keeping leaves, gunny bags, rotary or bamboo mountages and drier are needed for effective rearing of silkworms. The steps involved in rearing process of silkworm are disinfection of rearing house, incubation of eggs, brushing, young larval rearing and late age larval rearing.

The selected healthy silk moths are allowed to mate for 4 hours. Female moth is then kept in a dark plastic bed, it lays about 400 eggs in 24 hours; the female is taken out, crushed and examined for any disease, only certified disease-free eggs are reared for industrial purpose. The eggs are incubated in an incubator. The small larvae (caterpillars) hatch between 7-10 days.

These larvae are kept in trays inside a rearing house at a temperature of about 20°C – 25°C. These are first fed on chopped mulberry leaves. After 4-5 days fresh leaves are provided. As the larvae grow, they are transferred to fresh leaves on clean trays, when fully grown they spin cocoons. Their maturity is achieved in about 45 days. At this stage the salivary glands (silk glands) starts secreting silk to spin cocoons.

Post Cocoon Processing

The method of obtaining silk thread from the cocoon is known as post cocoon processing. This includes stifling and reeling. The process of killing the cocoons is called stifling. The process of removing the threads from the killed cocoon is called reeling. For reeling silk the cocoons are gathered about 8 – 10 days after spinning had begun. The cocoons are first treated by steam or dry heat to kill the insect inside.

This is necessary to prevent the destruction of the continuous fibre by the emergence of the month. The cocoons are then soaked in hot water (95° – 97°C) for 10-15 minutes to soften the gum that binds the silk threads together. This process is called cooking.

The “cooked” cocoons are kept in hot water and the loose ends of the thread are caught by hand. Threads from several cocoons are wound together on spinning wheels (Charakhas) to form the reels of raw silk. Only about onehalf of the silk of each cocoon is reelable, the remainder is used as a silk waste and formed into spun silk. Raw silk thus obtained is processed through several treatments to bring about the luster on the thread.

Uses of Silk

1. Silk fibers are utilized in preparing silk clothes. Silk fibers are now combined with other natural or synthetic fibers to manufacture clothes like Teri-Silk, Cot-Silk etc. Silk is dyed and printed to prepare ornamented fabrics. They are generally made from Eri-silk or spun silk.

2. Silk is used in industries and for military purposes.

3. It is used in the manufacture of fishing fibers, parachutes, cartridge bags, insulation coils for telephone, wireless receivers, tyres of racing cars, filter fibres, in medical dressings and as suture materials.

Diseases and Pests of Silkworm:

The profitable silk industry is threatened by various diseases caused by the virus, fungal, bacterial and protozoan infections but also by insect predators, birds and other higher animals. Ants, crows, kites, rats, feed upon silk worms thereby causing a great loss to silk industry.

Pebrine, is a dangerous disease to in silkworms and the causative organism is Nosema bombycis, a protozoan. This silkworm disease is transmitted through the egg of the mother silkworm and also through ingestion of contaminated food.

Flacherie generally occurs in the mature larvae and is caused mainly by bacteria like Streptococcus and Staphylococcus. Grasserie is a most dominant and serious viral disease. It is caused by Bombyx mori nuclear polyhedrosis virus (BmNPV) a Baculovirus, which belongs to sub group ‘A’ of the Baculoviridae. Among the fungal diseases, white muscardine is common. This disease is caused by fungus Beauveria bassiana.

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Vermiculture Definition and its Advantages

Vermiculture is the process of using earthworms to decompose organic food waste, into a nutrient-rich material capable of supplying necessary nutrients which helps to sustain plant growth. The aim is to continually increase the number of worms to have a sustainable harvest.

The excess worms can either be used to expand a vermicomposting operation or sold to customers. Vermicompost is the primary goal of vermiculture. Technically the worm castings are pure worm waste and are fine and nutrient rich organic soil amendment.

Vermicompost on the other hand, is comprised of the castings, bits of bedding and other organic matter. Essentially, though the terms are used interchangeably, they are both worm manure and are valuable for improving soil health. Applications of earthworm in technology of composting and bioremediation of soils and other activities is called Vermitech (Sultan Ismail, 1992).

The disposal of solid wastes (biodegradable and non – biodegradable) remains a serious challenge in most of the countries. Earthworms play a vital role in maintaining soil fertility; hence these worms are called as “farmer’s friends”.

These are also called as “biological indicators of soil fertility”. The reason is that they support bacteria, fungi, protozoans and a host of other organisms which are essential for sustaining a healthy soil.

The breakdown of organic matter by the activity of the earthworms and its elimination from its body is called vermicast. It is a finely divided granular material and is noted for its porosity, aeration, drainage and moisture holding capacity and serves as rich organic manure. Earthworms are divided into two major groups. The first group, the humus formers, dwell on the surface and feed on organic matter.

They are generally darker in colour. These worms are used for vermicomposting. The second group, the humus feeders, are burrowing worms that are useful in making the soil porous, and mixing and distributing humus through out the soil.

There are different endemic (native) species of earthworms cultured in India for vermicomposting such as Periyonyx excavatus, Lampito mauritii, Octochaetona serrata. Some earthworm species have been introduced from other countries and called as exotic species Eg. Eisenia fetida, Eudrilus eugeniae.

Vermicomposting

Vermicompost is the compost produced by the action of earthworms in association with all other organisms in the compost unit. Vermicompost bed may be selected on upland or an elevated level as it prevents the stagnation of water. You may construct a cement pit of 3x2x1m size (LxWxD) over ground surface using bricks. The size of pit may vary as per availability of raw materials.

Cement pot or well rings are practically good. Provision should be made for excess water to drain. The vermibed should not be exposed to direct sunlight and hence shade may be provided (Figure. 12.1). The first layer of vermibed contains gravel at about 5 cm in height, followed by coarse sand to a thickness of 3.5 cm, which will facilitate the drainage of excess water.

Earthworms collected from native soil prefer a layer of local soil in their compost beds. If local soil earthworms are used, add a layer of native loamy soil for about 15 cm on top of the gravel sand layer and introduce earthworms into it.

For exotic species such as Eisenia fetida and Eudrilus eugeniae, the layer of soil is not needed. The unit can now be loaded with digested biomass or animal dung such as cow dung that has lost its heat.

The number of earthworms to be introduced in an unit depends on the size of the vermibed prepared. Earthworms such as Periyonyx, Excavatus, Eisenia fetida or Eudrilus eugeniae are introduced on the top. Jute bags or cardboards or broad leaves are used to cover the unit. As worms require moisture, water management is most important for the survival of the earthworms. Too little or too much of water is not good for the worms.

Earthworms release their castings on the surface. One can start harvesting this from the surface on noticing the castings on the surface. It may take several days for the entire biomass to be composted depending on the amount of biomass.

When all the compost is harvested, earthworms can be handpicked by creating small conical heaps of harvested compost and leaving in sunlight for a few hours. The earthworms then move down and settle at the bottom of the heap as a cluster.

Earthworms from the lower layers of the compost can be recovered and the worms can be transferred to new composting units. Vermiwash is a liquid collected after the passage of water through a column of vermibed. It is useful as a foliar spray to enhance plant growth and yield. It is obtained from the burrows or drilospheres formed by earthworms. Nutrients, plant growth promoter substances and some useful microorganisms are present in vermiwash.

Earthworms can be used for recycling of waste food, leaf, litter and biomass to prepare a good fertilizer in container known as wormery or wormbin. Earthworm Pests and Diseases Earthworms are subjected to attack by a variety of pests.

Most outbreaks are the result of poor bed management. Earthworm enemies include ants, springtails, centipedes, slugs, mites, certain beetle larvae, birds, rats, snakes, mice, toads, and other insects or animals which feed on worms.

The earthworm has a number of internal parasites including numerous protozoa, some nematodes, and the larvae of certain flies. Larger predators can be excluded from worm beds by proper construction of the bins, and by use of screens or gratings at the bottom and top of the beds.

Advantages of Using Vermicompost

People are aware about benefits of organic inputs in farming. Vermicompost is excellent organic manure for sustainable agropractices. So, marketing vermicompost is now a potential and flurishing industry. Retail marketing of vermicompost in urban areas is most promising.

Vermicompost is neatly packed in designed and printed packets for sale. People of different age groups are involved in the production and selling of vermicompost. Marketing of vermicompost can provide a supplementary income.

1. Vermicompost is rich in essential plant nutrients.
2. It improves soil structure texture, aeration, and water holding capacity and prevents soil erosion.
3. Vermicompost is a rich in nutrients and an eco-friendly amendment to soil for farming and terrace gardening.
4. It enhances seed germination and ensures good plant growth.

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Scope of Zoology Science and its Importance

Studying Zoology can provide self employment opportunities and you can become an entrepreneur. Economic Zoology is a branch of science that deals with economically useful animals. It involves the study of application of animals for human welfare.

The need of Zoology is not just to improve our economic condition but also to provide food security and provide employment opportunities. Based on the economic importance, animals can be categorized as:

• Animals for food and food products
• Economically beneficial animals
• Animals of aesthetic importance
• Animals for scientific research

Zoology offers immense scope to a candidate who has done master’s degree in the subject. They can work as Animal Behaviourist, Conservationist, Wildlife Biologist, Zoo Curator, Wildlife Educator, Zoology faculty, Forensic experts, lab technicians, and Veterinarians.

Tools and Techniques in Biology:
Animal Physics

Structure and Function of Genes:
Animal Behaviour

Genetics Evolution:
Ecology

Cell and Molecular Biology:
Embryology

There are generally not a plethora of employment opportunities with a zoology degree, unless you have some connections and experience that have you ready to go. It is also not a lucrative field. However, if you have a passion to study animals or do related research, it’s a pathway.

B.Sc Zoology and B.Sc Botany are the two most popular B.Sc courses under Life Science. The scope of both B.Sc Zoology and B.Sc Botany is wide and can be a good option for candidates who want to go for research work in future that involves the study of living forms in the ecosystem.

Zoologists are also hired for zoos, wildlife services, botanical gardens, conservation organizations, national parks, nature reserves, universities, laboratories, aquariums, animal clinics, fisheries and aquaculture, museums, research, pharmaceutical Companies, veterinary hospitals, etc.

Chemistry has more scope than zoology and botany. If you want to pursue your career in teaching and in research then go for zoology and botany whereas in chemistry you have other scopes to work with Food manufacturing industries, chemical industries, pharmaceutical industries also teaching and research.

They are both “hard”. There is a lot of science and math in each. However, both botany and zoology are broad topics covering many sub-subjects. If you enter university to study one or the other of these, you will probably narrow your interests, and probably your career, by the time you graduate.

Designing and conducting research projects and studies of animals. Studying the characteristics of animals and their behaviors. Collecting and analyzing biological data and specimens. Writing papers, reports, and articles that explain research findings.

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Mechanism of Hormone Action

Hormones circulate in the blood but their concentration can increase or decrease based on the requirement of the body. This is controlled by feedback mechanisms. These mechanisms control the secretion of endocrine glands by stimulating the hypothalamus, pituitary or both, which inturn governs the secretion of a particular hormone.

In positive feedback, the secretion of the hormone increases where as in negative feedback further secretion of hormone slows down. Feedback mechanisms are the key factors for maintaining homeostasis in our body.

Hormones are classified into three major groups as peptide hormones, steroid hormones and amino acid derived hormones based on their chemical structure.

Peptide hormones cannot cross the phospolipid cell membrane and bind to the receptors on the exterior cell surface. They are are transported to the golgi, which is the site of modification. It acts as a first messenger in the cell. Hormones on binding to their receptors do not enter the target cell but generate the production of second messengers such as cyclic AMP (c AMP), which in turn regulates cellular metabolism.

This is catalyzed by the enzyme adenylate cyclase. The interaction between the hormone at the surface and the effect brought out by cAMP within the cell is known as signaling cascade. At each step there is a possibility of amplification. (Figure 11.17)

• One hormone molecule may bind to multiple receptor molecules before it is degraded.
• Each receptor may activate several adenylate cyclases each of which make much cAMP.
• Thus there is more signal after each step.

The actions of cAMP are terminated by phosphodiesterases. The effect of peptide hormones like insulin, glucagon, somatotropin are usually short lived because they work through second messenger system.

Steroid hormones can easily cross the cell membrane, and bind to their receptors, which are intracellular or intranuclear. Upon binding to the receptors, they pair up with another receptor – hormone complex (dimerize). This dimer can then bind to DNA and alter its transcription. (Figure 11.18)

The effect of steroid hormones such as aldosterone, oestrogen, FSH are long lived, as they alter the amount of mRNA and protein in a cell. Amino acid derived hormones are derived from one or two aminoacid with a few additional modifications. Thyroid hormone is synthesised from tyrosine and includes the addition of several iodine atoms.

Epinephrine an amino acid derivative may function through second messenger system like peptide hormones or they may actually enter the cell and function like steroid hormones.

Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).

There are two modes of hormonal action. A: Activation of cell-surface receptors and coupled second-messenger systems, with a variety of intracellular consequences.

Hormone levels are primarily controlled through negative feedback, in which rising levels of a hormone inhibit its further release. The three mechanisms of hormonal release are humoral stimuli, hormonal stimuli, and neural stimuli.

This type of mechanism is shown by lipid soluble hormones such as fatty acids and steroids that can easily pass through the plasma membrane. They possess intracellular receptors. The hormones bind to the target receptor that activates the enzymatic activity of the cell to bring about biochemical changes.

Mechanism of hormone action is not the same in all categories of hormones is a proteinaceous hormone, has large molecular weight and is insoluble in lipids, therefore, it cannot enter the target cell. Thus, it binds with the membrane bound receptor present on ovarian cell membrane.

The action involves secretion of by the thyroid gland into the circulation, uptake of target tissues, activation or inactivation of by deiodinase enzymes, binding of to nuclear receptors that act as ligand-regulated transcription factors, and regulation of expression of target genes.

What is the most common mechanism of hormone control? With negative feedback, the most common mechanism of hormone control, some feature of hormone action directly or indirectly inhibits further hormone secretion so that the hormone level returns to an ideal level or set point.

Hormones bind to specific proteins (hormone receptors) in the target tissues and produce effect on them. There are two types of receptors: membrane bound receptors (hormone receptors present on the cell membrane of the target cell) and intracellular receptors (receptors present inside the target cell).

The mechanism by which peptide hormones act upon specific target tissues to evoke characteristic functional responses is believed to be initiated by interaction with a highly special- ized portion of the plasma membrane, the so called hormone receptor site.