Aspects of Reproductive Biology of the Mussel, Brachidontes Pharaonis (Fischer, 1870) (Mytilidae:bivalvia: Mollusca) From the Northwestern Coast of Suez Gulf, Egypt

Abstract

Reproductive cycle of the two populations of Brachidontes pharaonis (Mytilidae: Bivalvia: Mollusca)at Adabia and Ain Sokhna (northern western coast of the Suez Gulf), was studied during the period from January to December 2014. The present results showed that sex is separated in this species, but the microscopic examinations are necessary for determination of gonads in both sexes. The first appearance for gonads was observed in males and females at 6.3and 6.5 mm shell length, respectively. However, the largest immature individuals reach 8.6 mm shell length. The overall sex ratio indicated to over dominant females at both sites, with 1:1.57 (males: females) at Adabia, increased slightly to 1:1.81 (males: females) at Ain Sokhna, with statistical significant differences (X 2 = 8.33 and 5.14 significant at P<0.001 and P<0.05), respectively. Gonads of both sexes appeared scattered within mantle tissues at both left and right sides of the animal. Mature male testes have whitish or creamy color, while females ovaries are more conspicuous, appeared lobulated and composed of a large numbers of oogenic follicles occupying most of the mantle depending on stages of egg maturation. In early stages, ovaries appear small in size, translucent, and have small oocytes. The sexually matured females have dark yellow to orange ovaries due to occurrence of full ripe ova full of yolk granules. Based on oocyte maturation, five developmental stages were recognized, comprised: stage I (immature), stage II (early stage of development), stage III (maturing stage), stage IV: late developing stage (ripe and spawning egg) and stage V (spent stage). Each developmental stage was characterized and identified by its specific features. The average values of mantle index and developmental stages showed that, the populations of B. pharaonis at Adabia and Ain Sokhna have lengthy breeding seasons extends from September to the end of the following April, with two peaks of spawning in early spring and late autumn at Adabia, extends through early and late spring, and through autumn at Ain Sokhna. The oocyte diameter varied from 30.