Silver carp is a native species of China where it has been raised in ponds since historic times. Nowadays, this species is farmed in almost every major continent. In fact, silver carp is the most widely fish species cultured in the world.

HABITS:

Silver carp is a plankton feeder fish, so it occupies the upper region (surface waters) of culture ponds. As plankton feeders throughout life, silver carp is indispensable for polyculture, which is widely practiced in China. Silver carp is not very competitive with other adult fish, is less susceptible to disease, and grow rapidly. Silver carp and bighead are competitive in their diet since both are plankton feeders. Thus, when these two species are cultured together, they are never stocked in equal numbers; the number of silver carp is usually smaller since they feed more actively than bighead.

SPAWNING:

Some of the fish used for egg production have themselves been reared in captivity, while others are brought in from the wild every year. Female broodfish are about 4-5 years old at first spawning, weighing in average 6 kg. Fish are stocked in pre-spawning ponds at a density of 1.5-2 t/ha. The sexes are kept together. Females are chosen after examination of the flexibility and the roundness of the abdomen. The genital papilla should be pinkish. Males will have spermatozoa in their testes. Ovulation is induced by the administration of hypophysial extract from common carp, LRH-A and HCG. These are the doses: first injection, carp hypophyseal extract, 0.4 mg/kg; second injection, carp hypophyseal extract, 3 mg/kg + HCG, 800 IU/kg. Spermiation can be induced by the injection of carp hypophyses (2 mg/kg) in a single dose. Ovulation takes place 6-8 hours after the second injection. Previously, male and female broodfish are put into circular concrete tanks in which ovulation, egg release, and fertilization occurs. The ovulation rate is about 70%. After fertilization, eggs are removed in buckets and placed in concrete incubation units or in glass jars. The optimum temperature for incubation is between 25 and 28° C.

GROWTH:

The larval rearing phase lasts for the first summer. The end product is a young fish of 16-20 cm length in the autumn. The on-growing production cycle varies with the region in which the species is being cultured. Three main factors affect the cycle and the yields obtained: polyculture of separate or mixed age classes, organic fertilization, and feeding. In China, the production cycle lasts for two years: in the first year silver carp are grown to 50 g, and reach 500-1000 g after the second year. At this point, fish are sold.

USES:

Silver carp presents several desirable characteristics that are sought for by aquaculturists, e. g., it is a fast-grower fish able to feed on the lowest level of the food chain (phytoplankton). Silver carp is also used as a means of biological control of algal populations due to its high filtering rates.

CULTURE:

Silver carp is usually raised in polyculture with other carp species. The overall aim of this practice is to make the best use of the production in the water body and to ensure equilibrium between the different species in their different ecological niches. Silver carp is chosen the principal species if ponds have been heavily fertilized. This species may also be raised in cages, raceways, rivers, lakes and canals.

REFERENCES:

Konradt, A. G. 1966. Methods of breeding the grass carp Ctenopharyngodon idella (Val.) and the silver carp Hypophthalmichthys molitrix. FAO World Symposium on Warm Water Pond Fish Culture. FR: IV / E-9.

Jhingran, V. G., and R. S. V. Pullin. 1985. A hatchery manual for the common, Chinese and Indian major carps. Asian Development Bank, Manila, and ICLARM, Manila.

Tsuchiya, M. 1967. Grass carp and silver carp: production of fry. Midori Shobo Book Company, Tokyo.

Van Der Kraak, G., N. W. Pankhurst, R. E. Peter, and H. R. Lin. 1989. The antigenicity of human chorionic gonadotropin in silver carp (Hypophthalmichthys molitrix) and goldfish (Carassius auratus). Aquaculture, 78:81-86.