VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

MANAGEMENT OF A TYPICAL FISH FARM

AIM: To know the management practices followed in a typical fish farm

• A typical fish farm consists of a
  • Nursery pond 
  • Rearing pond 
  • Production pond

Types of pond	Use
Nursery pond	To grow spawn and hatchlings of fish to fry state (2.0-2.5 cm ) for a period of 10-15 days
Rearing pond	To rear the fish fry to fingerlings of 10-15 cm size - which is ideal for stocking in production systems - for a period of two to three months
Production pond	To rear the fish fingerlings to a marketable size. Their production would vary depending on the species cultured and the preference of the consumers. Carps would reach a marketable size of 1 kg in 5-6 months.

Production pond

• The various management measures followed for each type of pond in a farm are
  •  Clearing of algal blooms and weeds 
  •  Eradication of weed fishes and other unwanted animals 
  •  Fertilization and liming 
  •  Release of spawn /hatchling/fingerling  (Stocking)
  •  Feeding 
  •  Harvesting
   

Clearing of algal blooms and weeds

• The algal blooms are sudden outbursts in association with fertilization. These blooms along with different types of aquatic weeds liberate good amount of carbon dioxide absorbing the available oxygen, leading to its depletion during night. It is reported that the carbon dioxide at a concentration of 20-30 ppm may be responsible for large-scale fish mortality. Hence, suitable measures have to be undertaken to eradicate these unwanted aquatic flora. Algal blooms are invariably caused by unicellular and filamentous algae and may impart colour to the water. The groups of algae which are responsible for bloom are

  • Chlorophyseae (green algae)
  • Chrysophyseae (golden-brown flagellates)
  • Myxophyseae (blue-green algae)
  • Bacillariophyseae (Diatoms)
  • Blue green algae are responsible for the development of persistent blooms where as others cause temporary blooms.

Effect of algal blooms in fish

•  As the algae are tiny they choke the gills of fish leading to death. 
•  The toxins from the algae cause fish death. 
•  Algal growth and decay leads to depletion of oxygen levels in water eventually causing stress and mortality of fish.

Control methods

• Chemical methods 
• Biological methods
• In chemical method of controlling algae, copper sulphate at a dose of 800g/ha is packed in cloth bags and immersed in ponds. Use of aluminum sulphate is also in practice to precipitate phosphate which is essential for algal growth, thus retarding the algal bloom. In biological methods, algal blooms are controlled by introducing other aquatic plants that would compete for nutrients and space. Duck weed or Lemna sp. can be inoculated into ponds which shade over the algae and causes death. Algal feeding fishes like silver carp can also be stocked to reduce the algal bloom. Bigger aquatic plants can be removed either mechanically or by biological methods.

Eradication of weed fishes and other unwanted animals

• Species of unwanted or undesirable fishes that are present in the production ponds are called weed fishes. These weed fishes or insects that are present in the ponds would feed upon the fish hatchlings or spawn resulting in production losses. Hence the predatory weed fishes and insects should be eradicated before the fishes are stocked.
• Poisons that are derived from plants, chlorinated hydrocarbons and organophosphates are commonly used for the eradication of weed fishes. Application of vegetable oils like groundnut oil, castor seed oil are also used and they are sprayed in the form of emulsion in the ponds for the eradication of insects.

Fertilization and liming

• For fertilization of the ponds, organic manure like cow dung is applied at the rate of 10,000 to 15,000 kg/ha in the form of paste in different locations of the ponds. The organic matter is decomposed by the bacteria resulting in the release of potassium, nitrogen, phosphates and carbon-di-oxide that would promote the growth of phytoplankton which is an important live food for fishes. Liming of pond is done by the application of common lime (quick lime-calcium oxide) at the rate of 300 kg/ha in combination with the fertilization. Liming and fertilization improves the fertility the water. Lime also act as an antiseptic. It also neutralizes the old organic deposits at the bottom . It also stabilizes the pH of the water and improves the growth of live food (Phyto and zoo plankton)
• The two types of fertilizers used in fish farms are organic and chemical fertilizers
  • Organic manure: Farm manure like cow dung, pig dung and poultry manure and liquid manure (sewage wastes) are used at the rate of 20-30 t/ha. This level can be reduced by 50% if chemical manures are also applied
  • Chemical fertilizers: The quantity to be used varies depending on the concentration of phosphorous and nitrogen in the soil. Urea at the rate of 200 kg/ha/year, superphosphate at the rate of 250 kg/ha/year and muriate of potash (Potassium chloride) at the rate of 40 kg/ha/yr can be applied in equal installments alternating with organic fertilization.

 

Stocking of fishes

• The stocking densities of the fishes to be followed for the different types are as follows:

Type of pond	Fish	Stocking density (No of fishes stocked/ha)
Nursery	Spawn of hatchling	1 million
Rearing	Fry	500 to 1 lakh
Production	Fingerling	10,000

Feeding of fishes

 

Type of pond	Feed and Feeding
Nursery	For feeding the spawn, a mixture of ground nut oil cake and rice-bran in the ratio of 1:1 is mixed and broad casted. The weight of daily feed upto first five days may be four times the total initial weight of seed fish and then eight times the initial weight between 6th -10th days.
Rearing	The hatchlings in nursery ponds feed on phyto and zooplankton that is grown in the ponds. When the growth of plankton is less, supplementary feed is given. Powdered ground nut oil cake and rice bran can be mixed in equal proportions soaked in water for 10-15 minutes, made into small balls and fed using the feeding trays kept in the pond. Artificial fish feed with 40% protein can be given at the rate of 4% of body weight. Vitamins, yeast, cobalt chloride and antibiotics can also be supplemented in feeds
Production	The feed and feeding is similar to that of rearing pond. Depending on the life stage and growth of the fish, their feed requirement can be adjusted

Harvesting

• Harvesting of fry in the nursery pond and rearing pond is done during early hours of either morning or evening. During harvesting, the water is gradually drained and the fishes are netted. Depending on the need and marketablility, partial or complete harvesting is done in the production ponds.