A QUANTITATIVE ASSESSMENT OF THE REPRODUCTIVE-BIOLOGY OF CYCLONAIAS-TUBERCULATA (BIVALVIA, UNIONIDAE)

Two hundred and thirty-three purple wartyback unionids (Cyclonaias tub erculata) were collected approximately monthly over a 31-month period from Kentucky Reservoir (Tennessee river mile 201.3), Tennessee, betwe en August 1988 and February 1991. An equal sex ratio and only one case of hermaphroditism were discovered. Histological examinations showed that spermatogenesis and oogenesis occurred throughout the year except during late summer and early fall. ''Typical'' spermatogenesis was mo st evident between May and July. Spawning occurred between early sprin g (March-April) and late summer (August). Brooding variation among fem ales was shown by the presence of embryos in the suprabranchial chambe rs and gills between early April and late August. Brooding was short t erm, as indicated by mature larvae being found in the outer demibranch s between early July and late August. Full demibranchs were never foun d, possibly indicating that the study took place during years of poor reproductive performance.