Composite fish culture

Fish ponds are a valuable source of protein and ready cash. Maximize production from your fish pond by raising combinations of between 3 and 6 complementary fish species which make best use of your pond's resources.

Pond preparation New ponds should be dug from clay loam soils. Avoid digging the pond on sandy soil.

- Narrow, rectangular ponds are easiest to manage. Allow for 0.2-0.4 ha in surface area and sloping in depth from 1.5 m to 2.5 m.

- Build the pond where it will be exposed to direct sunlight. Shade will reduce the pond's productivity.

- Apply lime to prevent fish diseases and parasites.

Manuring

Use raw cow dung at the rate of 10-15 tonnes per ha per year.

Add about 2.5 tonnes to the pond 15 days before stocking and the remaining quantity in 1 0- 11 monthly instalments. (If mahua has been applied to exterminate weed fish, forego the first application of cow dung.)

- Construct a bamboo crib to hold cow dung. Keep the crib filled with cow dung up to the water line.

- Defer application of cow dung for a few days if algal blooms appear and water becomes green.

- Add enough cow dung to make the water greenish-brown. This colour indicates there is plenty of natural food in the water.

Cow dung required (tonnes/ha/year)

Newly constructed pond	5.6 to 6.6
Pond which has been in use for some time	5.0 to 5.6
Old pond	0.7 to 0.5

Lime dosage

Highly acidic	2,000 kg/ha
Near neutral	500 kg/ha
Mildly alkaline	200 kg/ha
Highly alkaline	no lime

Use litmus paper to test your pond's acidity.

Stocking

Note

Variation in pH is harmful to fish. Lime your pond one week before manuring.

Crib to hold cow dung

Fish fingerlings for stocking can be purchased from government fish farms or from private growers. Stock in October-November.

About 10-cm-long fingerlings should be used for stocking. A pond with 2-3 m depth should be stocked at 6,000-10,000 fingerlings per ha. Depending upon the availability of fingerlings, the pond can be stocked with 3, 4, or 6 species in the following ratios:

Note

Fingerlings should be transported in cool weather. In hot weather, transport in the early morning or evening.

Species combinations and their stocking ratios

	3-species	4-species	6-species
Catla	4	3	1.5
Rohu	3	3	2.0
Mrigal	3	2	1.5
Common carp		2	2.0
Silver carp			1.5
Grass carp			1.5

Introduction of fingerlings

Fish

Right way-Release the fingerlings by gently tipping the plastic bag or container into the water.

Wrong way-Fingerlings should not be poured into the pond.

Feeding

Fish eat tiny plants and animals zooplankton and phytopinkton-which float in the water. Your goal is to maximize the growth of this natural food through proper management, which includes fertilizing the pond. Your fish will also need food supplements of oil cake (e.g., mustard or groundnut oil cake)

Frame filled with aquatic weeds to feed grass carp and rice bran.

Grass-eating fish, such as grass carp, will need a regular supply of weeds.

Part of the feed mixture can be broadcast at a fixed place. The rest of the feed can be made into a dough ball suspended in the water just below the surface.

To feed grass carp, suspend aquatic weeds on a frame made of bamboo and rope.

Weed clearing

Weeds take up nutrients, harbour harmful insects, consume oxygen, and block sunlight. They must be removed from the pond.

- Floating weeds, such as water hyacinth and pistia, can be removed by hand.

- Lighter floating weeds, such as spirodella, lemna and wolfia, can be removed by dragging a rope or small-mesh net across the pond surface.

Removing surface weeds

- Underwater weeds can be pulled up by dragging a length of weighted barbed wire Gr chain along the bottom of the pond

Rake your pond

Rake the bottom of your pond periodically to release nutrients. This can be done by dragging bricks along the bottom.

Dragging weighted barbed wire to remove underwater weeds

Note

After applying mahua, wait before introducing your new species. Wait longer if a heavy dose of mahua cake is given. The minimum waiting period is 24 hours.

Undesirable fish

Eradicate predatory or "weed" fish with mahua oil cake. Broadcast soaked mahua oil cake uniformly over the pond at the rate of 2-2.5 tonnes per hectare of pond surface, with a pond depth of 1 metre. Mahua oil cake is available in the market. Fish killed by mahua oil cake can be eaten.

Problems and solutions

If water level drops due to excessive evaporation	- add water to the pond.
If fish come to the surface with their snouts protruding for air (moat obvious	- stop applying manure and stop supplementary feeding.
	- add fresh water to the pond. ing from the water, gulp
	- beat the surface of the water with bamboo poles.
In the early morning)	- cut banana trunks into small bits and scatter them on the hand surface to help reduce acidity.
	- pull a drag-net through the pond several times for aeration.
	- apply potassium permanganate at 1 to 2 mg per litre.
	- apply lime at 300 to 500 kg per ha of pond surface.
If algal bloom forms	- release silver carp yn the pond, 500 per ha of pond surface.
	(Average weight of silver carp should be 100 9.)
If birds are eating your fish	- install scarecrows or other bird-scaring devices.
If your fish are being taken	- watch your pond more closely.
	- float branches in the pond. This will prevent netting.
lf fish become diseased	- net out the diseased fish and have them examined at the nearest government fisheries office for possible remedial measures.

Harvesting

Harvest the fish after one year when they have reached a marketable size of 0.6-1 kg If
the pond is threatened by flood, drought, or disease, consider harvesting early When netting, start from the deep end of the pond and drag the net slowly toward the shallow end

Cost and return from a one-hectare pond

Oil cake (3,000 kg @ Rs 5/kg)	15,000
Rice bran (3,500 kg @ Rs 2 50 /kg)	8,750
Labour (2 people) 360 person-days	7,200
	30,950
Interest 15%	4,642
	Rs 35,592
Income
Sales of 4,000 kg of fish @ Rs 22/kg	Rs 88,000
Net Profit
(Rs 88,000 - Rs 35,600)	Rs 52,400

Sources: Central Institute of Fisheries Education, Bombay and Dr. V. R. P. Sinha and Nirmal K Thakur