الملخص الإنجليزي
The knowledge of the biology of a species is essential to the understanding of its requirement to survive and reproduce in the wild or in controlled environments. This M.Sc. thesis focuses on the reproductive cycle of Laevichlamys ruschenbergerii, a species of scallop which occurs commonly on many coral reefs in the Sultanate of Oman. Monthly samples were collected from November 1998 to October 1999 in Bandar Khayran Bay, Muscat, Sultanate of Oman. Continuous temperature measurements were recorded on the reef. On average, each sample included 25 animals collected randomly from massive colonies of Porites coral by SCUBA at depths between 2 to 8 m. The populations were found to include almost twice as many females as males. Almost all large individuals >80mm) were found to be females, whereas most small individuals (<60mm) were found to be males suggesting an unusual case of protandry Gonadosomatic index (GSI) was calculated for each individual scallop (n=283). On average, the GSI measured for females (0.14) was almost double that of males (0.08) independently of the shell height. Five developmental stages of the ovaries were determined and characterized histologically: immature, developing, ripe, spawning, spent. Spawning of Laevichlamys ruschenbergerii was determined through measurements of GSI, coupled with histological observations of oocyte diameter and frequency distribution. Two relative decreases of GSI were observed synchronously between males and females in December 1998 and in March 1999. These are thought to correspond to 2 partial spawning events. Both spawning events corresponded to unusual fluctuations in temperature of about 2°C. Histological observations revealed a relatively low abundance of "spawning" and "spent" stages suggesting rapid spawning and recovery. On the other hand, the presence of ripe individuals of Laevichlamys ruschenbergerii in all samples, suggest that reproduction may occur throughout the year.
