Indian Major Crops
Indian major carp is a common name for several species of fish and commonly may refer to the following species now raised in aquaculture in South Asia and other Asian countries where they have been introduced.
- Catla is an Indian major carp. It is an economically important South Asian freshwater fish of the carp family.
- Mrigal is an Indian major carp, a ray-finned fish of the carp family native to rivers in India.
- The rohu is an Indian major carp, a fish of the carp family found in rivers in South Asia.
Broodstock maintenance :
A proper selection of brood fish is one of the most important aspects to obtain greater results in breeding and grow out. In general, farmers select the fast growing and largest fish on the assumption that these characteristics will be inherited by the progeny. However, it is not recommended to choose their offspring or same stock, as this results in inbreeding and poor growth rate and a significant number of deformed fry.
A minimum of three months before the breeding season the male and female fish has to be separated from the regular culture tank to avoid the unwanted breeding. During segregation, it is important to avoid stress while netting. Male and females can be identified through secondary sexual morphological characteristics, which develop during the season of reproduction. In males, the milt runs freely when abdomen is gently pressed and the females have a swollen abdomen due to the development of ovaries.
Spawning of Indian Major Carps :
Induced spawning is conducted during the onset of the southwest monsoon season (June) where there is an accumulation of rainwater in ponds and also a small reduction in temperature. The common carp pituitary is considered for better results, but in most cases, same species gland and Human Chorionic Gonadotropin (HGC) are used. The administered dose of pituitary gland depends on the maturity stage of fish, and environmental condition (rain and temperature).
A primary dose of 1 – 2mg/kg and the second dose of 6 – 8 mg/kg body weight of fish after six hours is administered. After injection, the brood fish has to be transferred into the breeding hapa following the ratio of two male for every one female. The breeding hapa is a box-shaped enclosure made using cloth. About 50,000 to 1,00,000 eggs are hatched in hapa of size 2 x 1 x 1 m. Facility to open and close the upper flap is also made available. The corners of the cloth in all sides are tied to poles to keep them intact.
Carp seed rearing:
Newly hatched larvae nourish themselves for 3 – 4 days, after which they depend on the natural feed from the environment. Availability of natural feed is most critical during the phase when it changes from the yolk sac nourishment to the commencement of natural feed, besides a suitable ecology to obtain greater survival percentage. Adequate care is to be taken before initial stocking.
The nursery pond is a pond where spawns are reared into fry. It takes 15 – 20 days with a lower water depth of 1 m. Nursery pond size of 0.02 to 0.1 ha is usually suitable for small-scale production and 0.5 ha for large-scale production. For fry rearing the seasonal ponds are preferred than the perennial ponds. Also small ponds have greater scope in terms of effective utilization than larger sized ponds.
Pre-stock pond preparation:
The carps spawn need to have good environmental conditions and food availability. Prior to release of the spawns, make sure there exist a congenial condition and adequate natural food organisms, which enhance the survival rate. A well prepared pond environment provides an optimum condition for a spawn. If its a drainable or seasonal pond, effective preparation include draining, drying, ploughing, liming, filling with water and fertilizer application. For perennial or undrainable ponds, besides the above mentioned steps, control of aquatic weeds and eradication of predatory and weed fishes are also to be take care of.
The pond productivity depends on the soil quality of the pond, such as pH, water retention, texture, total organic carbon, available nitrogen, and available phosphorus. Liming helps to improve the productivity by adjusting soil pH, mineralization of organic matter, the release of soil-bound phosphorus to water and disinfection of pond bottom.
Liming materials include agricultural lime (CaCO3), dolomite (CaMg(CO3)2) and Calcium oxide or Quick lime (CaO). The quantity of application varies with its effectiveness and soil pH. Generally, 200 – 500 kg/ha is applied to pond soil. After application, the bottom of the pond should be ploughed well to mix it with the surface soil.