Genetic Management of Hatchery-Based Stock Enhancement

Abstract

Including genetic considerations in stock enhancement can reduce the probability that enhanced (admixed) populations will undergo damaging genetic alteration through the stock enhancement effort. Avoiding alterations in genetic diversity, decreases in fitness, and reductions in effective population size (Ne) of admixed populations and their wild-population components is important for the long-term sustainability of those populations. Maintaining the genetic diversity of admixed populations and their wild-population components first requires managing both the genetic variability (e.g., numbers of alleles) and the genetic composition (frequencies of alleles) in the broodstocks and the broods. These genetic diversity components should be maintained at levels appropriate for each stock enhancement program throughout all aspects of stock enhancement—from broodstock selection through the rearing and releasing the broods and then, after release of the broods, in the admixed populations and their wild-population components until the admixed populations attain genetic equilibrium. Using small numbers of broodstock individuals, unequal contributions of broodstock individuals to broods, and inbreeding in broodstocks are common causes of alterations in genetic diversity. These pitfalls should be avoided because they can reduce genetic variability, change genetic composition, and increase genetic load (accumulation of deleterious alleles), which decreases the fitness hatchery broods. In an admixed population, reduction in the fitness of any population component (hatchery, wild, or their progeny) decreases the overall fitness of the admixed population. Hatchery brood fitness can also be reduced through outbreeding, which also ultimately decreases the fitness of the admixed population. Decreases in fitness of admixed populations or of any population components can extend over generations, particularly if stocking is repeated over multiple generations. The Ne of a population is directly related to losses in fitness due to inbreeding and reductions in genetic diversity. The smaller the Ne value of a population, the greater the chance that relatives will mate and that alleles (particularly rare alleles) will be lost over generations. Genetic monitoring programs for specific stock enhancement efforts Bert: Ecological and Genetic Implications ch08 Final Proof page 123 9.6.2007 11:40am Compositor Name: PDjeapradaban Theresa M. Bert (ed.), Ecological and Genetic Implications of Aquaculture Activities, 123–174.