Aquaculture System

Culture based on the economic or commercial considerations i.e. cultural operation type fish culture classified into five categories-

1.                  Extensive culture

2.                  Improve extensive culture

3.                  Intensive culture

4.                  Semi-intensive culture

5.                  Super intensive culture  

1. Extensive Culture: Extensive fish culture is the production of fish and water organisms using the natural food supply in ponds. Culture of herbivorous fish shortens the food chain. Fish growth per unit area of herbivorous fish is thus greater than with the production of predominantly carnivorous fish. The highest growth in extensive culture is achieved through polyculture of fish which feed on plants and those which feed on small animals.

Characteristics of extensive culture:

1.                  Extensive culture may be monoculture or polyculture.

2.                  Engineering design may not laid-out.

3.                  Very big ponds may not be fully cleaned.

4.                  No supplemental feeding.

5.                  Pesticides are not used.

6.                  Cropping frequency i.e., crop/yr is 1.

7.                  Cultivable species are variable sizes.

8.                  Stocking density is very low.

Operation: In this culture operation, all groups of cultivable fishes are cultured with the indigenous fishes but herbivorous fishes are more suitable in extensive fish culture. The stocked fingerlings which usually feed on the natural food namely phytoplankton, zooplankton and aquatic weed.

Fish species density: The stocking density is low as is the yield per unit area (e.g. 5000-10000 shrimp post larvae/ha/crop).

Production: Production is generally low at less than 1000 kg\ha\yr. Yield of fish ponds from larva to one summer under extensive management (polyculture) are as follows:

Advantages of extensive culture:

1.                  No care and no managed fish farming.

2.                  Simple production system this form of pond culture can provide food.

3.                  Generating new sources of employment for less qualified personnel.

4.                  Extensive culture presents no danger to the water quality in the pond.

5.                  Small capital expenditure.

6.                  Biodiversity remain stable.

Disadvantages of extensive culture:

1.                  Net income low.

2.                  High losses due to predators/poaching.

3.                  High provability of diseases or pests.

4.                  Lower survival rate (Approximately 20-30%).

2. Improve extensive culture: It is a form of extensive culture system, which is simplified to the extent that individuals or small groups of people can rear aquatic organisms with the less improve to the extensive culture for their own consumption at a rate that provides a relatively continuous supply.

Characters:

1.                  Improve extensive culture may be monoculture or polyculture.

2.                  Engineering design may not be well laid out.

3.                  Ponds may not be fully cleaned.

4.                  No artificial feeding.

5.                  Cultivable species are variable sizes.

6.                  Stocking density is low.

Operation: In this culture operation, all groups of cultivable fishes are cultured with the indigenous fishes herbivorous fishes are more suitable in improve extensive culture.

Different type of food stuffs have been used in improve extensive fish pond ranging from kitchen wastes, fishery and agro-industrial by products, wheat and rice bran, slaughterhouse wastes, damaged fruit terrestrial invertebrates etc.  

Advantages:

1.                  Little care and least managed fish farming.

2.                  Small capital expenditure.

3.                  Conservation of small indigenous fishes.

4.                  It is no danger to the water quality in the pond.

Disadvantages:

1.                  Fish growth per unit area is low.

2.                  High losses due to predators/poaching.

3.                  High provability of diseases.

4.                  Lower survival rate. (Approximately 40-45%)

3. Semi intensive culture: Semi intensive fish farming where fish/shrimp growth is depend upon the consumption of live food organisms and plants naturally present within the water body as well as a direct supplementary source of dietary nutrients.

The use of fertilizers can increase the natural production of the pond and hence its yield.

Characteristics:

1.                  Semi intensive culture should be monoculture.

2.                  Stocking density is higher than improve extensive culture.

3.                  Engineering design and layout with provisions for effective water management.

4.                  Fertilizer used regularly with lime.  

5.                  Pesticides used regularly for prophylaxis.

6.                  Water organisms receive natural food as well as supplemental feed.

7.                  Cultivable species are uniform sizes.

8.                  Water quality analyzed monthly.

Operation: In this culture operation, herbivorous and omnivorous fish species are particularly suitable for increasing fish production if the developing countries. The stocked fish which usually feed on the natural food and processed food.

Fish stocking density: The stocking density is higher than improve extensive culture (e.g., 50000-100000 shrimp PL/ha/crop).

Production: Production ranging from a minimum 1.5-5 ton/ha/crop to higher.

4. Intensive culture

Intensive fish farming is an aquaculture system where fish/shrimp growth completely depends on artificial feed.

Characteristics:

Ø    Intensive culture should be monoculture.

Ø    Higher stocking density.

Ø    Very well engineered system with pumps and aerators to control water quality and quality.

Ø    Fully cleaned pond.

Ø    Fertilizers are not used.

Ø    Pesticides used regularly for prophylaxis.

Ø    Cultivable species are uniform sizes.

Ø    Water quality analyzed weekly.

Ø    Intensive management.

Stocking density: Maximum 100 PLs/m².

Production: 20 tons/ha/year.

Advantages:

Ø    High stocking density.

Ø    Fishes survival rate higher (approximately 90%)

Ø    Low losses due to predators/poaching.

Ø    High yields (20 tons/ha/year in coastal area). 

Ø    High financial profit.

Ø    Low provability of diseases or pests.

Ø    Production fish with high market value (e.g., koral, thai koi)

Disadvantages:

Ø    Higher production cost.

Ø    Greater risks due to mechanical breakdown.

Ø    Reduction of biodiversity due to the cultivation of exotic species.

5. Super intensive culture

It is usually practiced in industrial countries to produce fish in artificial big tank where fish or shrimp growth completely depends on dry artificial feed.

Characteristics:

Ø    It should be monoculture.

Ø    Stocking rate is maximum.

Ø    Engineering design and layout with concrete tank.

Ø    Water quality analysed daily.

Ø    Cultivable species are uniform in sizes.

Stocking density: More than 100 PLs/m²

Production: 30-150 tons/ha/yr.

Advantages:

Ø    High stocking density.

Ø    Fishes survival rate higher (approximately 98%)

Ø    No losses due to predators/poaching.

Ø    Higher financial profit.

Ø    Low provability of diseases or pests.

Ø    Produce high value species.

Disadvantages:

Ø    Higher production cost.

Ø    Greater risks due to mechanical breakdown.

Ø    Reduction of biodiversity due to the cultivation of only desirable species.

Artificial feeding of fish

Artificial feed or feeding is one of the principle methods of increasing production in fish cultivation. Artificial feed is used in intensive culture system where fish/shrimp growth is totally depending upon the complete artificial feed. Artificial feed has a quality diet containing a predetermined nutrient profile. Traditionally it’s a dry or moist pelleted feed consisting of a combination of different feed ingredients.

Importance of artificial feed

Ø    To enhance fish productivity

Ø    To supplied balanced diet for cultured fish

Ø    For the proper growth of species

Ø    For repairing a damaged cells

Ø    To meet up specific requirements of individual items of foodstuff

Ø    To buildup the cell structure

Ø    For maintain physiological functions

Ø    To meet up caloric demand of fish

Forms of artificial feed

Feed types can take numerous forms. However, they basically fall into one of two general forms: dry and non-dry (moist). 

a. Dry feeds: Dry feeds are by far the most commonly used feeds in intensive aquaculture. Dry feeds are generally made from dry ingredients or from mixtures of dry and moist ingredients.  However, even though it may be implied by the name, these feeds are not entirely devoid of moisture, generally containing 6-10% water, depending on the environmental conditions. 

Dry feeds may be subdivided further. Feeds that are simple mixtures of dry ingredients are termed mashes or meals.

Dry feeds that are compacted into a defined shape, generally by a mechanical means, are called pellets. Depending on the formulation  and  compacting  techniques  these  diets  may  be  floating  or  non-floating (sinking) in water.

b. Non-dry feeds: Non-dry feeds can be either wet or moist. Generally, wet feeds

are  those  made  from  wet  ingredients  such  as  trash  fish,  slaughterhouse  waste, undried forage, etc., and contain 45-70% moisture. Moist feeds, on the other hand, are made from mixtures of wet and dry raw materials, or from dry ingredients to which water is added. The moisture content of these feeds ranges from about 18% to 40%. 

Non-dry  feeds,  both moist  and wet, may  be  either  extruded  to  forms  a  pellet  or non-extruded  (non-formed),  resulting  in  balls,  cakes,  etc.  during  the  process  of extrusion, the raw material is forced down a tapering shaft and through a die plate under  pressure  in  an  atmosphere  of  steam.  This  effectively  exposes  the  feed  to controlled  conditions  of  high  temperature,  pressure  and moisture.  The  extrusion process  cooks  the  carbohydrates,  primarily  causing  the  starch  granules  to gelatinize, and increasing the binding quality upon cooling. 

By altering the extrusion process, pellets of variable floating and/ or sinking rates may be produced. This is achieved by trapping air instead of water in the pellet as it leaves the high-pressure chamber. These air pockets are then stabilized by the rapidly cooling gelatinized starch. 

Extruded diets are known to be better utilized.  In certain instances extrusion of ingredients with high starch content, prior to Pelleting, is reported to have had an influence on the utilization of the diet.

Fertilization of ponds

Fertilization is the use of fertilizers to increase the production of natural food for fish. Considerable quantities of nutrient elements are regularly removed from the pond ecosystem through the harvested fish/shrimp crops and thus for retaining the pond fertility, the required amount of fertilizers need to be replenished.

Fertilization is necessary step in extensive and semi-intensive methods of farming operations.

Importance of fertilization

The fertilizers are used to increase fish production in ponds. The pond fertilization improves fertility in the following way:

Ø    It increases the production of the natural food organisms to be eaten by the fish. These organisms include phytoplankton, zooplankton and insects.

Ø    It does not cause dietary diseases.

Ø    It improves the hygienic condition of the pond by speeding up the decomposition of food residues and excreta.

Classification of fertilizers

Fertilizers are classified into two categories:

1.                  Inorganic or mineral fertilizers

2.                  Organic fertilizers or manures of plant and animal origin

1. Inorganic fertilizers: Commercially produced inorganic compounds containing major nutrients- nitrogen, phosphorus and potassium are known as inorganic fertilizers. Due to their high solubility in water the nutrients become readily available soon after their application, which helps to increase the primary productivity.

Inorganic fertilizers are-

a. Nitrogenous fertilizers: Sodium nitrate, ammonium nitrate, ammonium phosphate, ammonium sulphate, calcium ammonium nitrate, urea, ammonia liquor, etc., are the important nitrogenous fertilizers used in fish ponds.

Generally dose of nitrogenous fertilizer is 50 kg/ha. Generally 40-80 kg of urea are distributed per hectare every 15-20 days has been recommended for rearing ponds. Most of the nitrogenous fertilizers deplete reserves of bases and make soil acid.

b. Phosphate fertilizers: The most commonly used phosphatic fertilizers are the orthophosphates, superphosphates, dicalcium phosphate, triple super phosphate.    

Generally dose of phosphate fertilizers is 40 kg/ha. The optimum quantity seems to be 30-60 kg P₂O₅ per hectare.

c. Potassium fertilizers: Muriate of potash (KCl) and sulphate of potash (K₂SO₄) are the two commonly used fertilizers as a source of potassium. The favourable action of potassic fertilizers can be seen in ponds with low alkalinity, with peaty bottoms.

Generally dose of potash is 50 kg/ha. 

d. Calcium fertilizers: Calcium is usually applied in the form of lime, which is widely available as ground lime stone, slaked lime and quick lime.

Some of the actions of calcium fertilizers are to increase the pH of the tank, increase alkalinity and to precipitate organic matter.

The recommended application rate is 210 kg/ha annually.  

Above mentioned major nutrients are expressed on a percentage by weight basis. Nitrogen is expressed as %N and phosphorous as % P₂O₅. Commercially available inorganic fertilizers are usually sold with such trade names as 16-20-0 (16% N- 20% P₂O₅- 0%K), 45-0-0 (urea).

2. Organic fertilizers: The organic fertilizers are definitely of animal or plant origin and the nutrients present in them are either made available directly or after decomposition and transformation by the microbes.

The organic manures are generally recognized on the basis of the following criteria:

a. Organic manures with little or no carbohydrates: It has been found that the ponds treated with liquid manure a procured from the stables and byres (cow sheds) impart fertility for good fish yield. It is applied in small doses once or twice every 8 days in deeper parts of the pond. Stimulated growth of phytoplankton, filamentous algae and zooplankton has been noticed in ponds treated with liquid manures.

Increased yield through the use of guano and blood meal has also been reported.

b. Organic manures containing mainly carbohydrates: In this category, the manures made out of mustard oil cake, mahua oil cake, cotton seed meal, soyabean meal, etc.

Green manuring is used in fish ponds in many countries. In this method undecomposed green plant tissue is turned into soil by sowing a nitrogenous or other crop on dry pond bottom.   

c. Organic manures having considerable amount of carbohydrates with nitrogenous matter: They are available in a variety of forms such as farmyard manure (dung of cattle, sheep, pig and goal), poultry manure (poultry droppings), sewage (only diluted and pre-treated sewage can be used as a fertilizer), sludge (mud-like deposits or mixtures).

The rate of application for shrimp ponds ranges from 500 to 2000 kg/ha.

Advantages of organic fertilizers

1.                  It encourages bacterial growth, in turn favours better production of the zooplankton. It also stimulated growth of phytoplankton and filamentous algae.

2.                  It improves the bottom mud.

3.                  It increases the effectiveness of many inorganic fertilizers by providing the necessary organic matter base.

4.                  Organic fertilizers act as fish feed, i.e., organic fertilizers directly feed by fish.

5.                  They provide substrate for micro benthos attachment.

Disadvantages of organic fertilizers

1.                  There is a risk it might cause an oxygen deficit.

2.                  It favours certain diseases (gill rot).

Ref.

Gupta, S. K., and Gupta, P. C., (2006), General and applied ichthyology.

Marcel Huet, 1979. Textbook of fish culture Breeding and cultivation of fish.