Production of Carp Fry and Fingerlings
Commercial production of carp fry and fingerlings including stocking and pond management are explained here
Availability of required quantity of seed of the desired species at the appropriate time is one of the prime factors that lead to success of aquaculture operation. Though remarkable success has been achieved over the years in spawning the carps, availability of seed of desired size still remains a constraint. The nursery rearing involve nurturing of 72-96 hours old spawn which have just begun to eat and continues for a period of 15-20 days, during which they grow to fry of about 25-30 mm. These fry are further reared in another pond for a period of 2-3 months to raise the fingerlings of about 100 mm in size.
Nursery Pond Management
Small water bodies of 0.02-0.10 ha with depth of 1.0-1.5 m are preferred for nurseries though areas up to 0.5 ha can be used for commercial production. Drainable or non-drainable earthen ponds and cement cisterns are the different systems used for nursery rearing of fry.
The different steps involved in nursery raising of fry are discussed hereunder.
Pre-stocking Pond Preparation
Clearance of aquatic vegetation: Abundant growth of vegetation is undesirable in fish ponds as they absorb nutrients arresting the pond productivity, help in harbouring the predatory and weed fishes/insects hindering the free movement of fish and netting operations. Hence aquatic weed clearance is the first operation in pond preparation. Generally, manual methods are only used in nursery and rearing ponds, as they are shallow and small in size. In bigger ponds mechanical, chemical and biological methods can be used for eradication of aquatic weeds.
Eradication of predatory and weed fishes: Various predatory/weed fishes besides predatory animals like snakes, tortoises, frogs, birds, otters, etc present in ponds pose problems for survival of young fishes besides competing them for space and oxygen. Dewatering and drying the ponds or application of suitable piscicides are the methods adopted for eradication of predatory and weed fishes. Application of mahua oil cake @ 2,500 kg/ha-m three weeks before stocking of fish seed are suggested. The oil cake besides acting as piscicide also serves as organic manure after decomposition and adds to natural productivity. Application of commercial bleaching powder (30% chlorine) at dosage of 350 kg/ha-m of water is effective in killing the fishes. The quantity of bleaching powder can be reduced to half with the combination of urea @100 kg/ha-m, applied 18-24 hours before the bleaching powder application.
Pond fertilization : Planktons are the preferred natural fish food organisms that are produced by fertilizing the culture ponds. The ponds used for seed production are first limed after the removal of unwanted predatory and weed fishes depending on the pH of soil. After liming, the ponds are treated either with organic manures such as cowdung, poultry dropping or inorganic fertilizers or both, one following the other. Mixture of groundnut oil cake at 750 kg, cowdung 200 kg, and single super phosphate 50 kg/ha is found to be very effective in production of desired plankton. Half of the above amounts, after being mixed thoroughly by adding water to make a thick paste is spread throughout the nursery 2-3 days prior to stocking. The rest amount is applied in 2-3 split doses depending on the plankton level of the pond.
Control of aquatic insects : Aquatic insects and their larvae compete for food with the young growing fish and also cause large-scale destruction of hatchlings in nurseries. Application of soap-oil emulsion (cheap vegetable oil @ 56 kg/ha with 1/3 its weight of any cheap soap) is a simple and effective method to kill the aquatic air-breathing insects. Kerosene @100-200 l or diesel @75 l and liquid soap @ 560 ml or detergent powder @ 2-3 kg per hectare water area can be used as substitute to make the emulsion.
After three days of hatching, the spawn are transferred to the nurseries. The stocking is done preferably during morning hours by acclimatizing them to the new environment. The normal density of spawn recommended for earthen nursery is 3-5 million/ha. However, higher densities of 10-20 million/ha can be followed in cement cisterns. In nursery, monoculture of carp species is usually recommended.
Post-stocking Pond Management
The phase fertilization is done in 2-3 split doses during the culture period of 15 days as discussed earlier. Finely powdered mixture of groundnut oil cake and rice bran at 1:1 ratio by weight are provided as supplementary feed @ 6 kg/million for the first 5 days and 12 kg/million spawn per day for the subsequent days in two equal installments. With adoption of scientific methods of rearing, the fry attain the desired size of 20-25 mm with survival of 40-60% in 15 days rearing period. Since nursery-rearing period is limited to 15 days, the same nursery can be utilized for multiple cropping, at least for raising 2-3 crops in case of earthen ponds and 4-5 crops in case of cements cisterns.
Fry-Fingerlings Rearing Pond Management
Ponds of comparatively bigger in size than that of nurseries and preferably up to 0.2 ha area is used for rearing pond, i.e., for rearing fry to fingerlings. The different steps involved are as follows:
Pre-stocking Pond Preparation
The practices of pre-stocking pond preparation viz., clearance of aquatic vegetation and eradication of predatory and weed fishes are same as discussed in nursery pond management, while measures for control of insects are not necessary in case of rearing pond management. The ponds are fertilized with organic manures and inorganic fertilizers, the doses of which depend upon the fish poison used. If mahua oil cake is used as fish poison, the amount of cowdung application is reduced to only 5 tonnes/ha, but with other poisons having no manurial value, cowdung is applied generally at the rate of 10 tonnes/ha. While about one third of the dose is applied as basal dose 15 days prior of stocking, rest are applies fortnightly doses. Urea and single supper phosphate @ 200 kg and 300 kg/ha/year, respectively are also recommended for fortnight application in split doses as inorganic fertilizer source.
Stocking of Fry
Determination of the rate of stocking depends mainly on the productivity of the pond and the type of management measures to be followed. The normal stocking density of fry suggested for rearing ponds is 0.1-0.3 million/ha. While nursery phase is limited to monoculture, rearing phase involve polyculture of different carp species similar to that of grow-out production.
Post-stocking Pond Management
A feeding rate of 5-10% followed for fingerlings rearing. While in most of the cases the supplementary feed is limited to the mixture of groundnut oil cake and rice bran at 1:1 ratio by weight, non-conventional ingredients can also be used to compound the feed. When grass carp are stocked, duckweeds like Wolffia, Lemna and Spirodela are to be provided. Maintaining water levels of about 1.5 m depth and intermittent fertilization as mentioned earlier are the other management measures suggested. With adoption of scientific methods of rearing, the fingerlings attain 80-100 mm/8-10 g with a survival of 70-90% under rearing pond conditions.