(Jyotish Barman and Homeswar Kalita)
The common carp (Cyprinus carpio) is one of the candidate species in composite farming system. They also form one of the dominant fish species under rice-fish farming system.The species is more suitable for culture in hilly and cold region where the major carps could not sustain. It is one of the important species for culture in Nagaland. Common carp are mainly bottom dwellers but search for food in the middle and upper layers of the water body. The fish can survive cold winter periods, low oxygen concentration (0.3-0.5 mg/litre) as well as supersaturation. Carps can reach 0.6 to 1.0 kg body weight within one season in polyculture system.
Food and feeding habit:
Common Carp are usually omnivorous but mostly prefers water insects, larvae of insects, worms, molluscs and zooplankton. Additionally, the carp consumes the stalks, leaves and seeds of aquatic and terrestrial plants, decayed aquatic plants, etc. They also accept supplementary diet such as oil cake, rice bran, etc.
Breeding and seed production:
Common carp generally breeds in confined water. In tropical areas, the fish breeds two times from January to March and from July to August. Spawning takes place in shallow marginal, weed infested areas. Breeding is carried out in hapas, cement tanks or small ponds. Submerged aquatic plants are used as substrata for egg laying. When the fry are 4 to 5 days old, they are stocked into nursery ponds.
Prior to proposed breeding season, healthy male and female common carp should be segregated and stock in separate ponds or tanks. The breeders should be fed every day with artificial food comprising a mixture of oil cake and rice bran in 1:1 ratio at the rate of 2-3% of the total body weight.
Selection of breeders:
At the time of breeding operation, healthy and ripe breeders are transferred to condition hapa for screening. Care is taken not to put too many fish inside the hapa to avoid injury to breeders.
Hapa or cisterns are commonly used for breeding operation. For one set, female and male in the ratio of 1:1 by weight are stocked in each hapa. The numbers of set depends upon the size of the breeding system. The water used for breeding purpose should be fresh and free of algal bloom.
Since the eggs of common carp are adhesive in nature, aquatic plants like Hydrilla and Najas, palm or coconut fibres and synthetic fibres of gunny bags are normally used as egg collector. The size of the egg collector should be double the weight of the female brooder. The materials should be washed thoroughly before introducing into the hapa.
In case where facilities such as hapa and cisterns are not available and breeding of common carp has to be done in the pond, small plants of water hyacinth with long hanging roots are introduced in the ponds as egg collector. The plants with attached fertilized eggs are then transferred to well prepared, predatory free nursery ponds for hatching after breeding.
Spawning of common carp mostly occurs during night to early morning. Hence, the breeders are usually introduced into the hapa or tank in the evening hours. Spawning usually takeswithin 6- 10 hours of introduction. After spawning the brooders are released into the pond. The egg collectors are then examined for fertilization. The fertilized eggs are pale dirty yellow in colour and are less conspicuous than the unfertilized whitish opaque eggs.
The egg collectors with attached fertilized eggs are then either transferred to well prepared, predatory free nursery ponds for hatching or to hatching hapas.
The hatching hapa is a double walled enclosure with the outer hapa being made of bolting cloth (0.5 mm mesh) and the inner hapa is made of mosquito net cloth enclosure (2.0-2.5 mm mesh) which is fixed in the pond by using four bamboo poles. The attached eggs are later uniformly distributed inside the inner hapa. Hatching time usually varies from 36-72 hours depending on the water temperature. Once hatching is completed, the hatchlings escape to the outer hapa and the inner hapa containing egg shells is removed. Newly hatched hatchlings possess a prominent yolk mass and stick to the egg collector for a day. When the egg mass is completely absorbed hatchlings are found suitable to be stocked in nursery.
Breeding through hormone administration:
Stripped spawning: The selected males and females are induced by either carp pituitary gland extract or inducing agent such as ovaprim, ovatide or WOVA-FH @ 0.2 ml/kg weight. The fish are then kept in hapa for few hours. When the female is ripe for stripping, the eggs are stripped into a container and are thoroughly mixed with the male spermatozoa (known as egg-milt mixture). Since the eggs are adhesive in nature, it is essential to remove the adhesiveness at once to make the eggs free-floating for incubation. To remove adhesiveness, cream milk powder (20 g) is dissolved in 1 litre of water andthe egg-milt mixture is then treated for 45 minutes and stirred to ensure separation of individual eggs.
Spontaneous spawning: Breeding is conducted either in earthen pond or cement cistern and the spawns are reared in the pond itself. Egg collectors are provided in for attachment of eggs in this type of spawning. The female brooder is induced with synthetic hormone @ 0.2 ml/kg weight and is then released into the spawning pool which contains synthetic fibre. Soon after breeding, broods are removed and the eggs are incubated there till they hatched out which usually start after 36-72 hours. Once hatching is completed, eggs collectors are removed and washed thoroughly which can be re-used several times.