Methods to Describe Fish Stocks

Abstract

The description of the genetic diversity of species is a prerequisite step for both basic (understanding of mechanisms involved in the adaptation and evolution of species) and applied (management of the genetic resources of species) purposes. This description includes two major phases. One is a proper identification of the species under consideration. From a theoretical point of view, the species is clearly defined as a community of individuals which can interbreed in the wild and produce fertile progenies. However, this biological concept of species is difficult or impossible to apply and, in practice, many species are still recognized on a morphological basis. In the case of the fishes which exhibit a large phenotypic plasticity (Aliendorf et al., 1987), this typological approach does not lead to adequate identification of species in many situations. The second phase is the description of the intraspecific structure of the genetic variation and the identification of elementary breeding units. These units are defined as communities of individuals of opposite sex which have, a priori, the same probability to interbreed and to produce a fertile progeny. This mating system is called panmixy and each panmictic breeding unit a population. It must be emphasized that the population is the major evolutionary unit of the species and, therefore, should be the major management unit.