One of the Indian major carps, it has been cultured since historic times in the plains of northern India (the Ganges river system).

HABITS:

Rohu is column feeder in ponds. Larvae and fry feed on unicellular algae and zooplanktonic organisms. Adults feed on various type of vegetable matter including decaying aquatic plants, algae, etc. The species occurs in still water in the natural river systems. A diurnal species and usually solitary. Burrows occasionally.

SPAWNING:

For many years a major obstacle to the development of culture of rohu and the other major Indian carps has been the inability of culturists to consistently breed them in captivity. All species spawn naturally in rivers. In aquaculture facilities, the major carps may be spawned in specially constructed reservoirs, or bunds, where there is enough current to approximate river conditions. This technique may be used only in areas where the topography permits. Induced spawning with the aid of pituitary injections is more generally applicable. Breeders are usually selected from 1.5- to 5-kg, 2 to 4-year-old fish stocked in spawning ponds a few months prior to the breeding season, which usually coincides with the southwest monsoon, then segregated at maturity. Intramuscular injections are made on the caudal peduncle or near the shoulder region. Females are injected two or three times, while males receive only one injection. The first injection, of females only, consists of 2 to 3 mg of pituitary extract/kg of body weight, after which the sexes remain separated for 6 more hours. Then males are given a dose equal to the first injection administered to females, while the females receive a second dose of 5 to 8 mg/kg. Following this injection, the fish are placed together in groups of three (two males and one female) in covered breeding hapas. Spawning ordinarily takes place within 3 to 6 hours. Once the eggs have hardened, 8 to 10 hours after spawning, they are transferred, in batches of 75,000 to 1,000,000, to hatching hapas set in marginal waters of ponds, where they hatch in 15 to 18 hours at 27-31ºC.

GROWTH:

Rohu are seldom left in growing ponds longer than 3 years. Most fish are sold after the first year, when they have attained weights of 675 to 900 g. Rohu grows considerably less than catla. On the other hand, growth rates of rohu and mrigal (other major Indian carp) are comparable.

USES:

Rohu has been widely introduced outside of its native range where it is used for stocking reservoirs and aquaculture. It is mostly consumed fresh.

CULTURE:

Polyculture is the most common practice in the rearing of the major Indian carps. To this end, several species combinations and stocking rates have been developed. The traditional Indian major carp culture in India is an extensive production system with only limited fertilization. The different species are stocked in varying ratios, the most common being: catla, 30%, rohu, 60%, mrigal, 10%. When calbasu is included, the percentage of rohu is reduced to 50 to provide for 10% calbasu. By altering these ratios according to the primary production in the ponds, and more intensive stocking and supplemental feeding with locally available foodstuffs like oilcake and rice bran, higher rates of production have been obtained.

REFERENCES:

Krishna-Moorthy, P.; Manohar, L. 1996. Effects of different dosages on the concentration of sulphadiazine in the tissues of the fish, Labeo rohita (Hamilton). Journal of Ecobiology 8:123-128.

Mukhopadhyay, N.; Ray, A.K. 1996. The potential of deoiled sal (Shorea robusta) seed meal as a feedstuff in pelleted feed for Indian major carp, rohu, Labeo rohita (Hamilton), fingerlings. Aquaculture Nutrition 2:221-227.

Rajyashree, M. 1996. Carbamide induced alterations in some metabolic aspects of the fish Labeo rohita. Journal of Ecotoxicology and Environmental Monitoring 6:41-44.

Vijayalakshmi, S.; Tilak, K.S. 1996. Effect of pesticides on the gill morphology of Labeo rohita. Journal of Ecotoxicology and Environmental Monitoring 6:59-64.