Effective population size and rate of inbreeding in aquaculture of Indian major carps

Abstract

Induced spawning of Indian major carps by hypophysation has been practiced extensively since the mid-nineteen-fifties. At present, all hatcheries function as isolated genetically closed units raising their own stock of breeders and producing fish seed for distribution to grow-out areas. The individuals for replenishment of broodstock are those which were retained after the hatchery has reached its seed production target for a given year. There is a growing concern that hatchery stocks may be severely inbred because their overall performance has been rapidly deteriorating. Exact estimates of the rate of inbreeding accumulation, however, is difficult because the effective population size is not known and systematic records of various broodstock management operations are not available. In this paper, effective population size ( N e) and the rate of inbreeding ( ΔF) have been estimated in terms of the numbers of new individuals entering the broodstock population each year and the variance of their reproductive success. This study is based on data collected during the 1987–1988 breeding season from 18 fish hatcheries in Karnataka State, southern India. N e ranges from as low as 3 to a maximum of 30, and ΔF from 2% to 17% per year. Rapid inbreeding of stocks is evident. Possible ways of reducing further accumulation of inbreeding in broodstock populations are discussed.