Disturbed Sexual Characteristics in Male Mosquitofish (Gambusia Holbrooki) from a Lake Contaminated with Endocrine Disruptors. (Research)

Article excerpt

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 holbrookl) 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. Key words: antiandrogen, courtship behavior, endocrine disruption, estradiol, mosquitofish, sex characters, sperm count, testosterone. Environ Health Perspect 111:695-701 (2003). doi:10.1289/ehp.6022 available via http://dx.doi.org/[Online 23 January 2003]

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Reproductive abnormalities have been observed in several wildlife populations living in polluted areas (Guillette et al. 1996; Howell et al. 1980; Jobling et al. 1998). In laboratory studies, it has been confirmed that environmental contaminants with endocrine-disrupting properties (EDCs) can disturb the development and expression of sexual characteristics in fish (Gimeno et al. 1996; Gray and Metcalfe 1997), amphibians (Hayes et al. 2002), reptiles (Crain et al. 1999; Willingham and Crews 1999; Willingham et al. 2000), birds (Feyk and Giesy 1998), and mammals (Gray et al. 1994, Sharpe et al. 1995). However, the extent to which the sexual characteristics and reproductive capabilities of natural populations are impacted by these EDCs is still not well understood.

Because of a chemical spill in 1980, Lake Apopka, Florida, is extensively polluted with dicofol, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and its metabolites 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane (DDD) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE). In addition, various pesticides, such as toxaphene, trans-nonachlor, dieldrin, and aldrin have been released into the lake from the surrounding farmland and are commonly found in the wildlife living in this area. A series of reproductive abnormalities have been reported in alligators living in this lake (Guillette et al. 2000), including reduced clutch size, altered gonadal morphology, smaller penis size, and altered hormone concentrations. Furthermore, elevated levels of environmental contaminants have been found in eggs and plasma of alligators living in Lake Apopka (Guillette et al. 1999; Heinz et al. 1991). It has been suggested that the elevated levels of contaminants in Lake Apopka cause these reproductive abnormalities (Guillette et al. 1994). However, the long generation time and large body size of alligators makes it a protracted and difficult task to verify the effects of chemical exposure in a controlled laboratory setting. …