Reproductive cycle and gonad development of the commercial clam Donax trunculus from the Bay of Tunis (Northern Tunisia, South Mediterranean coast): effects of environmental variability

In Tunisia the commercial exploitation of Donax trunculus is limited to the unregulated catches which threaten the biological sustainability of this species. Knowledge of the gametogenic development of a species is a prerequisite for proper management and sustainable exploitation of this fishery. The reproductive cycle of D. trunculus from the Bay of Tunis was carried out between November 2006 and January 2008, using the dry weight changes, the histological examination of the gonad and the measurement of oocyte size. Results showed that, sex ratio were in favor of males without any hermaphroditism. The gametogenesis activity of both sexes, started with decreasing seawater temperature during late autumn and the main spawning event took place from June to October when temperatures rose. During this time, clams loose, gradually, their weights and condition and maturity indices reached their lowest values immediately after spawning period. The mean oocyte diameter varied significantly between 12.1 +/- 9.8 mu m in early gametogenesis and 45.9 +/- 13.6 mu m during maturity. Considering these data, a closed season from May to July coinciding with the most intensive gamete release should be considered for the preservation and the management of the natural stock of D. trunculus from the Bay of Tunis.