Development of mosquitofish (Gambusia affinis holbrooki) populations in lentic mesocosms. Perspectives for ecotoxicological studies.

In the perspective of ecotoxicological assays in mesocosms, the development of mosquitofish populations (Gambusia affinis holbrooki) has been assessed . The objective was to evaluate the ability of fish to reproduce in these e xperimental ponds under the climatic conditions of Brittany, and to see if population size and individual criteria were related to the number of adult s initially introduced. Six mesocosms (3.2 m diameter and 0.7 m water depth ) similarly designed received sexually mature mosquitofish at the rate of 1 2 (6 females and 6 males), 6 (3 females and 3 males) and 2 (1 female and 1 male) in June 1996. Each assay was duplicated. In December 1996, the entire populations were collected and the weight, size and sex of the individuals were noted. Length-frequency distributions were relatively similar between mesocosms and the different mode groups showed that the reproductive activ ity occurred until the beginning of fall. The produced biomass (from 4.1 to 38.3 g) and number of fish collected (from 26 to 301) were statistically c orrelated to the number of pairs initially introduced. This study provides interesting perspectives for ecotoxicological investigations in which the e ffects of pollutants on mosquitofish would be assessed at the population le vel.