Aquaculture for all

Intersex Traits Raise Concerns About Run-off

US - A recent study has found that male fish may develop female characteristics when exposed to run-off in areas of intensive agricultural production. The findings, which also support previous discoveries in Canada, could have implications for human health.

Researchers at the National Fish Health Research Laboratory found an increased incidence of both male and female sexual characteristics in smallmouth (Micropterus dolomieu) bass in the Potomac River, Virginia.

The condition, known as intersex, was exhibited in one sex - in this case, male bass were found to have oocytes or female germ cells in a male sex organs. It has previously been shown to occur when male fish are exposed to Oestrogen hormones. In this case it is believed that run-off caused as a result of agricultural activities, such as pesticide spraying, has influenced the hormone balance, causing disruptions. Similar observations have been reported in Canada where fish populations were exposed to wastewater containing the hormones altered egg formation in female minnows (Pimephales promelas).

The research conducted by Blazer, Iwanowicza, Smith, Young, Hedrick, Foster and Reeser, noted that in 2003, during health assessments conducted in response to mortality and a high prevalence of skin lesions observed in smallmouth bass in the South Branch of the Potomac River, the presence of immature oocytes within testes was observed.

The scienctists subsequently developed an index (0–4)to evaluate the severity of the condition. Data was collected from 2003 to 2005 and the findings were statistically evaluated.

High Prevalence

The highest prevalence and severity were consistently noted during the prespawn–spawning season, when compared with the postspawn season.

In 2005, smallmouth bass were collected at selected out-of-basin sites in West Virginia where fish kills and external skin lesions have not been reported, as well as at sites in the Shenandoah River, Virginia (part of the Potomac drainage), where kills and lesions occurred in 2004–2005.

This research was conducted by researchers at: US Geological Survey, National Fish Health Research Laboratory, 11649 Leetown Road, Kearneysville, West Virginia 25430, USA US Geological Survey, Aquatic Ecology Branch, 11649 Leetown Road, Kearneysville, West Virginia 25430, USA West Virginia Division of Natural Resources, 1 Depot Street, Romney, West Virginia 26757, USA US Army Corps of Engineers, Huntington District, Post Office Box 9, Apple Grove, West Virginia 25502, USA Virginia Department of Game and Inland Fisheries, 517 Lee Highway, Verona, Virginia 24482, USA

Further Reading

- To view an abstract and details on the research paper click here.
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