Aspects on the reproductive cycle of Donax semistriatus and Donax trunculus (Mollusca: Bivalvia) in Idku, Egypt

摘要

Present study deals with the reproductive cycle of the two clams Donax semistriatus and Donax trunculus (Bivalvia: Mollusca) and it is the first in this region. Specimens of these animals were collected monthly from two sites, one of them located at waterway that discharges waste water from irrigation canal. The reproductive stages of D. semistriatus and D. trunculus were classified into: inactive, early active, late active, ripe, partially spent and spent stages. Males of D. semistriatus were higher than females at both sites (male: female ratio was 1.47:1 in site 1 and 1.54:1 in site 2). Meanwhile, male D. trunculus outnumbered females in site 1 (1.38:1), and females made up a slightly higher proportion than males (1:1.13) in site 2. The sexual cycle of both species showed inactive gonad in the winter while the sexual activity was mainly detectable during spring and summer. Both species showed no signs of hermaphroditism. Temperature is found to be the factor which possibly triggers reproduction.