Authors
Fahrenthold. D.

Title:
Male Bass in Potomac Producing Eggs. Pollution suspected cause of anomaly in river's south branch

Source:
Washington Post. Oct. 15, 2004. Page A01.

Summary:
An article in the Washington Post reports the finding of abnormal sexual characteristics of male bass in West Virginia's Potomac River (Fahrenthold, Oct. 15, 2004). This discovery was made during an investigation of reports that fish in the south branch were developing lesions and dying at an unusual rate. Dissection of fish, mainly smallmouth bass, revealed the presence of eggs in the testes of 42% of the males investigated.

Altered sexual parameters in wild species, such as amphibians, reptiles, and birds inhabiting contaminated areas have been extensively documented. Endocrine disruption has been widely accepted as a plausible hypothesis for the unusual sexual development of many species. Exogenous hormones, such as natural and synthetic estrogens, as well as compounds which have estrogenic properties have been extensively examined for their potential role in the feminization of wildlife. The mechanism by which these compounds induce feminizing effects is likely through binding to the estrogen receptor which subsequently leads to increased gene transcription and synthesis of estrogen regulated proteins. Compounds can also alter normal endocrine function by interfering with the production, transport, metabolism or excretion of naturally occurring hormones.

Many species of fish are gonochorisitic, which means that their sex organs pass through an undifferentiated stage from which ovarian and testicular differentiation proceed. Fish are especially susceptible to the external hormonal environment, and this plasticity in terms of sex determination and differentiation has long been exploited the aquaculture industry. Exposure of sexually undifferentiated larvae to high levels of estrogen produces an all female stock which often has desired growth characteristics as compared to males of the same species. Therefore the author's speculation that natural hormones found in poultry manure, or hormones in processed sewage may be responsible for the intersexuality discovered in male fish of the Potomac River are biologically plausible factors. The impact this may have for humans is not clear. The effects of exposure to the complex mixture of the many possible endocrine disruptors present in the environment and their interaction with biological systems remains unknown. Also, there is very little evidence investigating the human health impact of long term exposure to low concentrations of these compounds.

Although it is plausible that environmental contaminants are responsible for the observed abnormal sexual parameters in the male fish of the Potomac river, many other possibilities must be considered. A wide range of environmental conditions can also induce endocrine disruption. Factors including temperature, restricted food supply, pH, parasites, and stocking density have all been shown to influence sex determination in fish Also, due to the unique sexual development of fish, intersexuality is known to occur at a natural rate in wild fish populations. One of the most common symptoms of this phenomenon is the differentiation of previtellogenetic oocytes in differentiating testes, and some fish exhibiting signs juvenile intersexuality have been shown to eventually develop as normal males. Therefore, whether genetics, environmental conditions, contaminants, or a combination of these are responsible for the development of intra-testicular oocytes in male fish found in the Potomac river remains to be determined.