Reproduction of reef fishery species

Abstract

Although reproductive patterns in tropical fishery species are characterized by diversity, some interesting trends are clearly emerging, despite the few families studied in detail. Reproductive output is highly variable, both within and among species, years and individuals. Especially in larger species, the differential between the fecundities of different-sized conspecifics may be orders of magnitude. Environmental and biological factors influence when and where reproduction takes place, with annual spawning seasons ranging from as little as a week or two, to much of the year; the notion that tropical marine species are all characterized by protracted spawning is unfounded. Most species produce pelagic eggs and, characteristic of reef fishes in general, all produce pelagic larvae. Females may spawn a few times to many times annually. Spawning often takes place towards dusk, in some cases at specific times in the lunar or tidal cycle. Evidence for lunar cyclicity in most larger species, however, is not strong except among a number of species which aggregate to spawn. Spawning occurs in areas of residence or at well-defined aggregation sites, metres or many kilometres away from home sites. Males and females mate either pairwise or in small groups which characteristically comprise one female and several males; the size of the testis relative to the body (gonadosomatic index) of ripe males apparently accords with mating pattern - larger for group and smaller for pair spawners. Larger, more mobile, species within a family tend to migrate to reproduce in aggregations which are frequently, but by no means exclusively, located offshore and close to deep waters. Such sites may be quite distinct but there is no evidence to indicate that they are unique. It is not clear whether aggregation spawning and the preference for specific spawning locations evolved largely for the benefit of larval dispersal or survival, to enable males and females that live somewhat dispersed to come together or for some other reason.