The minor carps are commercially important fishes of the Cyprinidae family. The carps that are used in aquaculture include Reba (Cirrhinus reba), Bata (Labeo bata), Fringe-lipped carp (Labeo finbriatus), Calbasu (Labeo calbasu), white carp (Cirrhinus cirrhosus) and Cauvery carp (Labeo kontius).
The commercially important barbs are the Silver barb (Barbonymus gonionotus) and Olive barb (Systomus sarana) and they belong to the family of Cyprinidae.
The minor carp and barbs, except Cauvery carp, are normally distributed throughout India. Adults inhabit large streams and rivers They also exist in tanks, canals, ponds and beels. They primarily feed on plankton and detritus, but may also feed on mud, vegetables, crustaceans and insect larvae.
The brood fishes are reared in the earthen ponds. Before 2 – 3 months of the monsoon season, the brood fishes are separated from the commercial culture condition. The fishes that are more than two years old are separated into the broodstock tank at a stocking rate about 500 – 600 kg/ha. The local food such the mixture of Groundnut oil cake and rice at 1:1 ratio or commercial feed is provided at the rate of 2 – 3 percent of body weight of fish.
The selected brood fishes (minor carps and barbs) are administered with ova prim or ovatide at 0.3 – 0.4ml/kg body weight for female fish and 0.15 – 0.20 ml/kg body weight for male fish and then released into the spawning tank. The bunch of aquatic plants such the hydrilla is a prerequisite to facilitate the olive barb breeding. The stalked eggs are attached to the weeds of leaf surface and strands. The response time in all minor carp varies between 8 – 11 hrs and it depends on the water temperature (27 – 28oC). The fertilized eggs are collected from the breeding tank and is incubated into the circular incubation tank. Hatching out take place after about 15hrs, at an incubation temperature of 27 – 30oC. It is allowed for about another 60 – 62 hrs in the same tank until getting the spawn.
The spawn is reared in the earthen and cement ponds as well. The ideal pond size is about 0.5 – 1.0 acre, having an average water depth of 1.0m. In an earthen pond, larvae rearing of all minor carps take place at about 25 – 30 days. For silver barb it takes about 40 – 45 days due to small size spawn (3 mm). The spawn is stocked at about 20 – 40 lakhs per acre, which means 500 – 1000 spawns/ m2 in earthen ponds. Two to three times higher stocking density is practiced in cement cisterns.
The rice bran and the GNOC are mixed at 1:1 ratio, provided as supplementary feed for all minor carps. For olive barbs, rice bran (45 percent), Groundnut oil cake (45 percent) and dry fish meal (10 percent) are provided and for silver barbs, a mixture of soybean meal and egg up to 10 days and after that rice bran and Groundnut oil cake is provided as supplementary feed.
The ponds are prepared in similar way as that of the Indian Major Carps. The dried ponds are filled with water up to 20 – 30 cm, manuring is done with raw cow dung at 1200kg/acre. After two days, the water is raised to 1.0 m. In the case of perennial ponds, in addition to the above, the aquatic weeds are needed to be removed completely for which manual method is advocated.
Eradication of unwanted fishes
The presence of predatory and weed fishes in nursery ponds significantly affects the survival rate. These fishes normally spawn before carp spawning and increase their population. The larvae of predatory may compete with carp seeds for the food, space and oxygen, which affects the growth and survival rate. The dewatering and sun drying is the best method to remove the predatory and weed fishes. But if it is not possible, application of pesticides can be resorted to. The predatory and weed eradication is done through physical, plant derivatives and chemicals methods. The physical method such drying, hook and lines and repeated netting are used to eradicate weed fishes. In plant origin, the derris root power (4 – 20 ppm), mahua oilcake (250 ppm), tea seed cake (about 60ppm) are used for detoxification which take about 2 – 3 weeks. In chemical method, the bleaching power (350 kg/ha), urea and bleaching (add 100kg/ha of urea and after 18 hrs add 175kg/ha of bleaching powder) and anhydrous ammonia (10mg N/l) are used, for detoxification. These take about 1 – 2 weeks.
The water is to be maintained at pH of 7.5 – 8.5 which is considered suitable for the rearing of a nursery. If it is less than 7.5, liming should be done at about 80 kg per acre. The lime is applied uniformly in the ponds.
The phased manuring is recommended for the successful rearing of fry in nursery ponds because it maintains the sufficient level of plankton production. A total of 750 Groundnut oil cake, 200 kg of cow dung, and 50kg of super phosphate is applied in four phases such as before stocking, 6th, 11th and 16th day after stocking.
The minor carps and barbs are compatible to culture with Indian Major Carps with same feed and management practices. Minor carps and barbs are more suitable to rear in the temporary ponds, with the water retention of 5 – 7 months. The different species for multispecies stocking has been evaluated. The study revealed that stocking of IMC 4000/ha (catla – 35 percent, rohu – 40 percent, mrigal – 25 percent) and MCB 8000/ha (Silver barb – 40 percent, fringe-lipped carp – 35 percent, Olive barb – 25 percent) has produced an average yield of 3005 kg/ha with a food conversion ratio of 2.34 when compared to monoculture of IMC or MCB and other combinations of IMC and MCB. When minor carps are cultured with Indian Major Carps, it provides an additional 30 percent yield.