Acceleration and deceleration effects of hatchery rearing on salmonid development, and their consequences for wild stocks

Abstract

Cultivation, in maximising environmental advantages and minimising disadvantages, allows fish to develop more rapidly than in the wild. Farmed salmon tend to smolt and mature younger than wild-ones. Their developmental programme is genetically determined, but runs under environmental instruction. Their development may be altered by changing either the programmed (genetically) or the instructions (environmentally), or both. In practice both are changed, but to varying degrees. Abundant food improves opportunities, and so developmental processes are generally accelerated by this and by genetic selection for high growth rate. While early smolting is commercially desirable, concomitant early maturation is not. Later development may be decelerated by food restriction at critical seasons, and by selection for late maturity. The environmental manipulations per se, of fish which subsequently escape from rearing facilities have little biological significance for wild stocks, although the presence of large numbers of small mature fish may present fishery management problems. However, the genetic manipulations pose potential problems, since the genotypes of these fish have been altered to suit culture rather than wild conditions.