Disturbed sexual characteristics in male mosquitofish (Gambusia holbrooki) from a lake contaminated with endocrine disruptors.

Abstract

Previous laboratory studies have demonstrated that estrogenic and antiandrogenic chemicals can alter several sexual characteristics in male poeciliid fishes. Whether similar disturbances occur under field conditions remains to be confirmed. Lake Apopka, Florida, is contaminated with numerous chemicals, some of which possess endocrine-disrupting activity. Male mosquitofish (Gambusia holbrooki) were collected monthly from December 2000 through May 2001 from Lake Apopka and two nearby reference lakes, Orange Lake and Lake Woodruff National Wildlife Refuge. Selected sexual characteristics were compared temporally and among lakes during the collection period. Male fish from Lake Apopka had slightly shorter gonopodia and on average 32 and 47% fewer sperm cells per milligram testis, when compared with the fish collected from Orange Lake and Lake Woodruff, respectively. The testes weights increased markedly during spring, with significantly smaller testes in fish from Lake Apopka than from Orange Lake, but surprisingly, the smallest testes occurred in males obtained from the Lake Woodruff population. The highest liver weights were found in the Lake Apopka population. Whole-body concentrations of testosterone and estradiol varied among months; the peak testosterone concentration occurred in January and was significantly lower in male fish from Lake Apopka compared with Orange Lake. The intensity of male courtship behavior was highly correlated to body testosterone concentration, but no statistically significant differences in sexual behavior among the lakes were found. We conclude that sexual characteristics of relevance to male reproductive capacity are altered in the Lake Apopka mosquitofish population, and we discuss the presence of chemicals with antiandrogenic effects in Lake Apopka as a possible cause of the observed alterations.

Sex Determination Diversity and Sex Chromosome Evolution in Poeciliid Fish

“…In contrast, the western mosquitofish, Gambusia affinis , has a ZZ-ZW female heterogametic mechanism, with heteromorphic sex chromosomes including a large W chromo-some in females compared to 24 pairs of homomorphic chromosomes in males [Black and Howell, 1979]. Mosquitofish and other poeciliids are models to test for the presence and effects of endocrine disruptors in the environment [Toft et al, 2003].…”

Female masculinization and reproductive life history in the western mosquitofish (Gambusia affinis)

“…Male G. affinis from the same population had reduced testes mass compared to males in populations with masculinized females present. Similarly, male eastern mosquitofish (Gambusia holbrooki) from masculinized populations had shorter gonopodia, produced half as many sperm, and had smaller testes per unit body mass than males in non-masculinized populations (Toft et al 2003). These studies clearly indicate that masculinizing agents have the potential to strongly influence the reproductive output of both sexes.…”

Environmental Endocrine Disruption of Brain and Behavior

“…Reports abound for effects of EDCs on reproduction in fish, with virtually all of the studies focusing on the gonad, vitellogenesis in males, the manifestation of intersex gonads, alterations in secondary sexual characteristics, and/or reduced fertility (Bayley et al, 2003;Jobling et al, 2002;Koger et al, 2000;Toft et al, 2003; reviewed in Arukwe (2001)). Nevertheless, environmental EDCs are highly likely to exert effects on the fish brain, similar to those described above for mammals.…”