Reproductive cycle and gonad development of Venus verrucosa L. (Bivalvia: Veneridae) in Kaštela Bay, Adriatic Sea

Abstract

The warty venus (Venus verrucosa Linnaeus, 1758) is commercially one of the most important bivalves in the Mediterranean Sea. Studies of reproductive cycle and gonad development of this species were conducted in Kaštela Bay, eastern Adriatic Sea, in a period between March 2009 and February 2010. We analysed sex ratios, gonad developmental stages, perimeter of the oocytes, and length at sexual maturity using standard histological techniques. Sex ratios did not significantly deviate from the proportion of 1 : 1 (χ2=0.228, p=0.632) and hermaphroditic animals were not found. Venus verrucosa showed continuous annual gametogenic activity, without a resting period. Mean values of oocyte perimeter ranged from 163.7±72.4 µm in March to 370.57±95.16 µm in October. Significant correlation was found between mean gonad indices and temperature. Changes in condition index approximately followed changes in the reproductive cycle, while observed decrease in condition index in the period from July to November reflected prolongation of the spawning period. Although the reproductive cycle of V. verrucosa has been studied in other parts of the Mediterranean previously, this study provides the first qualitative data on maturation stages for this species in the eastern Adriatic as well as quantitative data on oocyte perimeters, that were not included in previous investigations.