Growth and production

Abstract

The family Cyprinidae is the most successful group of freshwater teleosts; representatives occur in most freshwater habitats in all the major continents, although their presence in Australasia results from introductions by Man. The family's ubiquity sterns in part from the wide range in growth rate and ultimate size shown by different species, often in the same river or lake. This feature, allied to the range of reproductive requirements (Chapter 17), means that most freshwater habitats are suitable for at least one species, and many habitats support several. In addition, there is frequently marked intraspecific variability in growth rate between different life his tory types (Fig. 16.1) and between sexes. This variation may reflect genetic adaptations to particular local environments, but the evidence from fish transfers (e.g. Mann and Steinmetz, 1985) suggests that individuals within a population show wide phenotypic plasticity. This plasticity confers the potential for a rapid response to changes in environmental conditions in an individual fish's growth rate and development to sexual maturity. Indeed, the sensitive response offish growth to manipulations of population density and of the nutrient status of the environment underlies much of fish culture practice. In this chapter, lexamine the principal factors that determine growth rates and production levels in cyprinid fishes, particularIy in natural populations. Both abiotic and biotic features of the environment are involved, although current thought is that the maximum potential growth rate, ultimate size and longevity of each species is under genetic control (review, Beverton, 1987). In addition, I describe the consequences of growth plasticity in relation to the onset of sexual maturity and to the level of recruitment of individual cohorts. However, it should be remembered that most of these relationships are not peculiar to the Cyprinidae. The majority of examples are for European species, with wh ich I am most familiar. In fact, many of the relationships described are relevant also to tropical cyprinids, although the difficulty of ageing in these