Life history responses of fishes to culture

Abstract

The protected environment in culture permits fishes to reduce the proportion of energy normally channelled into the costs associated with competition for food, shelter and mates, avoidance of predators and counteracting parasites and diseases. The surplus energy so released is allocated to growth and reproduction, accelerating development through increased growth rate, earlier maturation and increased relative fecundity. Cultivators manipulate the rearing environment to remove seasonal variation in availability of resources, so that the fishes grow and develop through otherwise unproductive seasons. Such environmental manipulations exaggerate the basic accelerative effects. Since maturation deflects energy from growth, farmers also manipulate the fishes nutritionally, physiologically, hormonally and genetically to postpone maturation. As environmental regulators determine sex in many fish species, environmental manipulation in culture may have unintended effects on sex ratios. Mortality in culture should be very low, but survival of fishes released from culture is rarely as high as that of wild conspecifics. Finally, while short life-cycles and simplified population age-structures permit high rates of production in farms, they lead to ecological instability when the fishes are cultured for support of wild populations. # 2004 The Fisheries Society of the British IslesLife-history strategies provide solutions to the problem of reproducing successfully in varying environments. Life histories are accounts of how animals partition the food energy needed to survive, grow, develop to maturity and reproduce. The developmental programme is genetic but it runs under environmental instruction. Fishes are ectothermal animals, so their development depends on external temperature. Photoperiod signals synchronize development with appropriate temperature conditions. Hence the life histories of fishes are strongly seasonal. Developmental rhythms evolve in synchrony with opportunities offered by environmental rhythms, which are signalled to the animal most reliably by photoperiod. Culture simplifies the range of environmental signals to which fishes are exposed and permits the cultivator to manipulate the fishes as physiological machines for his chosen variant of their life history, e.g., for high growth rate or high gamete production.Whatever the life-history variant, the necessary food energy is allocated first to maintenance needs, and the surplus partitioned between growth and reproduction Tel./fax: þ44 (0) 1796 47 3886;

Cultured Atlantic salmon in nature: a review of their ecology and interaction with wild fish

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Responsible Approach to Marine Stock Enhancement: An Update

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