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

Abstract

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 experimental ponds under the climatic conditions of Brittany, and to see if population size and individual criteria were related to the number of adults initially introduced. Six mesocosms (3.2 m diameter and 0.7 m water depth) similarly designed received sexually mature mosquitofish at the rate of 12 (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 activity 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 correlated to the number of pairs initially introduced. This study provides interesting perspectives for ecotoxicological investigations in which the effects of pollutants on mosquitofish would be assessed at the population level.Key-words : fish, Gambusia affinis holbrooki, mesocosm, population, reproduction. DÉVELOPPEMENT DE POPULATIONS DE GAMBUSIE (GAMBUSIA AFFINIS HOLBROOKI) DANS DES MÉSOCOSMES LENTIQUES. PERSPECTIVES POUR DES ÉTUDES ÉCOTOXICOLOGIQUES. RÉSUMÉDans la perspective d'études écotoxicologiques en mésocosmes, le potentiel de développement de populations de gambusie (Gambusia affinis holbrooki) a été évalué. L'objectif était de savoir si la gambusie se reproduisait dans ces systèmes expérimentaux soumis aux conditions climatiques de la Bretagne, et si l'effectif final et la biomasse des populations étaient proportionnels au nombre de géniteurs initialement introduits. Six mésocosmes (3,2 m de diamètre et 0,7 m de hauteur d'eau) constitués de façon identique ont reçu en juin 1996 des géniteurs de gambusie, à raison de 12 (6 femelles et 6 mâles), 6 (3 femelles et 3 mâles) et 2 (1 femelle et 1 mâle) individus par mésocosme. Chaque essai a été réalisé en duplicat. En décembre 1996, les populations ont été Article available at

Improving mesocosm data analysis through individual-based modelling of control population dynamics: a case study with mosquitofish (Gambusia holbrooki)

“…2) and on the length distributions ( Fig. 3) are consistent and can be interpreted based on the literature on mosquitofish population dynamics (Wainwright et al 1984;Botsford et al 1987;Drèze et al 1998;Benoit et al 2000). The existence of logical and mechanistic explanations for the outputs of the length distributions analysis strongly supports the relevance of the significant differences between the endpoints.…”

“…Thus, we compared control mosquitofish populations to populations founded by two and four times more individuals, either by using a few real control populations (as done usually in mesocosm studies) or by using the simulated probabilistic distributions of the endpoints in control conditions predicted by the model. As previously demonstrated (Drèze et al 1998), when the number of founders is increased the population should more rapidly reach the carrying capacity of the mesocosm, with consequences on population dynamics which could be logically interpreted.…”

“…Furthermore, in males, contrary to females, the onset of sexual maturation is known to coincide with a marked decrease in growth rate (Campton and Gall 1988) and males virtually stop growing after reaching sexual maturity (Zulian et al 1995;Pyke 2005), hence females grow much larger than males. The mosquitofish population dynamics could be monitored in a mesocosm within a few months (Drèze et al 1998). Accordingly, mosquitofish have been used for evaluating genetic and demographic responses of fish to pollutants in outdoor lentic mesocosms (Giddings et al 1984;Tatara et al 2002).…”