Freshwater aquaculture (2+1)

Unit 4 - Cultivable fish and their culture methods

4.1.2. Culture Practice
Carps are mostly cultured in three stages namely.

• Nursery Phase
• Rearing Phase and
• Grow – out phase

Nursery phase
Carp spawn, 72-96h old are reared up to fry size (25mm) in this phase in small ponds of size 200 to 1000 m2 with a depth of 1.0 – 1.5m. The rearing period lasts for about 15-20 days.
All the pond preparation procedures explained in the previous unit are followed. The steps followed are

• Drying – 3-5 days
• Ploughing
• Liming
• Fertilization
• Eradication of insects
• Stocking
• Supplementary feeding and
• Supplementary fertilization

Additional steps in undrainable ponds include

• Control of Aquatic weeds
• Eradication of predators and weed fish

Pond Fertilization:

• Nursery ponds are fertilized with inorganic and organic manures to promote production of phyto- and zooplankton. The fry of carps feed initially on zooplankton such as rotifers and cladocerans
• The ponds are first applied with lime @ 200-500 kg/ha and ploughed into the soil lightly. The ponds are then filled with water to a depth of 1.00 to 1.5 m. One week post liming cow dung is applied @ 5-6 tones/ha or with poultry manure @ 2-3 tones/ha, a fortnight before stocking.

Control of aquatic insects

• Insects and their larvae feed as carp spawn and fry or sometimes kill them by piercing their bodies. They also compete for food and space leading to poor survival of the stocked spawn. The population of insects increases enormously post fertilization. They multiply rapidly and spread from pond to pond by flying.
• Application of soap oil emulsion @ 56 kg soap to 18 kg cheap oil is a simple and effective means of insect control. These insects are air breathing. The soap oil emulsion floating at the surface of the water chokes their respiratory apparatus when the swimming up to the surface for breathing.

Stocking:

• The spawn ( 72-96h old) are transferred from hatcheries to nurseries during cool hours preferably in the morning.
• The optimum stocking density recommended for earthen nursery is 3-5 million /ha
• Higher densities of 10-20 million/ha can be followed for nursery rearing in cement tanks.
• Mono-species culture is usually followed at nursery stage. If rearing space is limited polycutlure can be followed.

Supplementary feeding:

• Spawn are fed with finely powdered mixture of oilcake and rice bran in 1:1 ratio to supplement the natural food.
• They are fed @ 600 g/lakh fry for the first five days and 1200 g/lakh spawn for subsequent days in two equal installments during morning and evening hrs. In about 15-20 days fry attain a size of about 25mm at which size they are transferred to rearing ponds.

Harvesting fry :

• Harvesting is done by repeated dragging with a fry net of 1/8 inch mesh. The quantity harvested is measured in perforated cups.
• Number harvested is estimated by multiplying the number of cups and average number of fry per cup.
• Survival rates vary from about 40-50% from June to September. 2-3 crops of fry can be raised in earthen ponds and 4-5 crops in concrete tanks.