Prevalence of a testicular anomaly in lake trout (Salvelinus namaycush) of the Great Lakes basin

This report examines the occurrence of a testicular anomaly in lake trout (Salvelinus namaycush) from the Great Lakes basin. The anomaly was uni- and to a much lesser extent bilateral constriction along varying lengths of either testis. Prevalence throughout the Great Lakes was similar ranging from 28% in Lake Michigan to 44% in Lake Erie, and was unrelated to rearing history, strain, age, or year for the period 1979 to 1985. The anomaly has been present in the Great Lakes drainage basin since at least 1927 Prevalence of testicular constrictions in lake trout from inland lakes that ranged from 2.8 to 13.7% was lower than in the Great Lakes. All salmonids in Lake Ontario were affected in the order lake trout > brown trout and rainbow trout > coho salmon and chinook salmon although a morphologically similar anomaly was also found in lake whitefish and round whitefish, lake herring, alewives, and white suckers. Lake trout front one inland lake had a smaller portion of the testis affected than lake trout from Lake Ontario where affected fish showed compensatory growth in the contralateral normal testis. Constrictions were equally prevalent in self-sustaining and non self-sustaining stocks, they affected a relatively small portion of the testis for which there was compensatory growth of the normal testis, and they did not block the sperm duct. The potential for testicular constrictions to affect lake trout reproduction in the Great Lakes while unclear seems low.