Energetics of Reproduction

Abstract

A fish can be viewed as a system that takes an input, food, providing energy and materials, which it ‘maps’ into an output, the progeny (Pianka, 1976). Its biological success is the number of progeny produced in its lifetime that reach sexual maturity relative to the number produced by other fish in the population. This ‘mapping’ depends on the somatic body of the fish which provides the framework and machinery that converts food into offspring. Reproduction usually requires more than just the production of gametes (Miller, 1979). It may involve the development of secondary sexual characters such as breeding colours and morphological features; pheromones may be released, and other secretions can include mucus for attaching the eggs to the substrate, or for nest building. All these will require the expenditure of energy in addition to the energy spent on the production of gametes. Reproduction frequently depends on complex behaviour which can include migration to the spawning grounds, territorial defence of spawning areas, complex courtship sequences and parental care. These behavioural activities also demand an expenditure of energy. Thus the energy costs of reproduction are threefold: first, those of the primary sex products, the eggs or sperm; secondly, those of the secondary sexual characteristics; and thirdly, those of reproductive behaviour.