Fish in Peril?

The largemouth bass is important ecologically and as a recreational fish species in Maryland lakes and rivers.

May 30, 2013

Largemouth and smallmouth bass in regional waters are increasingly being reported with evidence of endocrine disruption–specifically testicular-oocytes (TO), an intersex condition where male fish possess immature female eggs within otherwise normally developing testes.

The condition is widespread within studied Chesapeake Bay tributaries including the Potomac, Susquehanna, and Eastern Shore river systems. There is little agreement on the seriousness of the observed condition at a population-level. While largemouth bass populations are generally strong, smallmouth bass have suffered serious declines in the Potomac River system in recent years. Moreover, despite significant effort by state and federal researchers, no particular culprit has been identified as causing TO in regional bass. The prevailing theory is that exposure to one or more likely, several estrogenic contaminants in wastewater discharges or agricultural and urban runoff are responsible for feminizing the male fish. However, complications arise in establishing this causal link. The slow development of bass from hatch to reproductive maturity, generally several years, places a considerable disconnect between the periods of contaminant exposure and observed effect.


Aquatic toxicologist Dr. Lance Yonkos is sidestepping this disconnect by transferring the question from the field to the laboratory. By exposing hatchery-reared largemouth bass at various developmental stages to controlled levels of common regional pollutants, Yonkos aims to identify contaminants of particular concern and establish developmental windows of sensitivity. Initial investigations are already underway and include an undergraduate research group comprised of ENST students. Using poultry litter as the contaminant source-identified previously as estrogenic by Dr. Yonkos and colleagues–the team expects to demonstrate the utility of largemouth and smallmouth bass as model species for toxicological study and hopefully shed some light on the causes of intersex in regional fish.