Evaluation of a nonlethal technique for determining sex of freshwater mussels

The shells of most North American freshwater mussel species are not sexually dimorphic. During the brooding period, gravid females can be identified by inspection of marsupial gills; however, it is difficult to separate nongravid females from males in species lacking sexual dimorphism. The ability to differentiate males from females throughout the year would assist mussel conservation and research. Our objective was to test the accuracy and safety of a method to determine the sex of live mussels. We used a syringe to extract ???0.2 mL of gonadal fluid from 67 Elliptio dilatata and 65 Actinonaias ligamentina. The fluid was stained and examined microscopically for developing gametes. This method was safe and effective for determining the sex of mussels. After 1 y, survival was indistinguishable between test and control groups for both species. We sacrificed 4 to 7 E. dilatata and A. ligamentina at 3-mo intervals and examined histological sections of gonads. Sex assigned from examination of gonadal fluid and histological sections agreed in most cases (E. dilatata: 100%, A. ligamentina: 89%). ?? 2008 by The North American Benthological Society.