Intersex is a term used to indicate the presence of both male and female characteristics in an individual fish, including the presence of female oocytes within a male gonad or spermatocytes within a female gonad. Intersex has been observed in a number of fishes worldwide. While the cause(s) of intersex are not fully understood, many factors including exogenous steroids, temperature, behavior, and pollutants have been shown to influence sex differentiation in fish. Intersex, particularly testicular oocytes, in fish is being used more frequently as an indication of exposure to endocrine disrupting compounds (EDCs), including organochlorine pesticides, PCBs, heavy metals, pharmaceuticals, and surfactants. Currently, Pennsylvania Sea Grant staff are studying the prevalence of intersex in several species of fish from Presque Isle Bay Long Point Bay, Ontario, Canada. The results of these analyses will be used to inform our extension efforts.
In Pennsylvania, smallmouth bass are a socioeconomically and ecologically important species, supporting a popular recreational fishery. Recently, however, their populations have been in decline in several major rivers. Mortality of young‐of‐year (YOY) smallmouth bass was first documented in 2005 and again annually at varying degrees since 2005 in the West Branch Susquehanna, Susquehanna, and Juniata rivers. In addition, lesions and intersex have been observed in smallmouth bass in the Susquehanna drainage. In 2011, disease outbreaks similar to those seen in the Susquehanna River Basin were first observed outside of the drainage in the Allegheny, Schuylkill, and Delaware rivers. Currently, Pennsylvania Sea Grant is supporting three research projects to gain a better understanding of the cause(s) of smallmouth bass mortality in the Susquehanna River drainage, including what role parasites and contaminants play in the mortality.