35 INTRODUCTION Oyster aquaculture industry is one of the oldest aqua- culture activities worldwide. The evolution of this industry began in the 20th century after the establish- ment of reliable technologies (Lubet, 1991). In 2000, world production of aquaculture molluscs attained 10.73 millions of tones representing 30.15% of the aquaculture production in all sectors, which attained 35.58 millions of tones. The bivalve industry mainly concerned USA, China, Japan, Corea, France, Spain and The Netherlands (FAO, 2002). The major pro- duction was represented by oysters (37.37% of the total production in molluscs, 98.32% of which were Crassostrea gigas, 24.6% clams, 12.28% mussels, and 10.75% scallops Saint-Jacques (FAO, 2002). Crassostrea gigas in Tunisia has been farmed for the first time in the Bizert lagoon in 1972. Juvenile oysters were imported for the first time from Japan and then from France (Medhioub, 1993). This spe- cies has been studied by Gimazane & Medhioub (1979) and its growth was monitored in the Bizert lagoon for juveniles longer than 3 mm. Gimazane & Medhioub (1979) and Medhioub & Zaouali (1988) have showed that different attempts for spat culture performed in 1977/1978 in the Bizert lagoon and in 1988 in the Ichkeul Lake, were not successful. Oyster production in Tunisia is since then dependent on the importation of juveniles from France. Indeed, the spat quantity imported from France in 2002 was about 665 Kg corresponding to a total cost of 5500 € and in 2003 was about 595 Kg which corresponded to a total cost of 5520 € (INS, 2003). The purpose of this study was therefore to exam- Journal of Biological Research 5: 35 – 45, 2006 J. Biol. Res. is available online at http://www.jbr.gr Evidence for Crassostrea gigas reproduction in the Bizert lagoon of Tunisia SALWA DRIDI 1* , MOHAMED SALAH ROMDHANE 2 , ALEXANDRA LEITAO 3 and M’HAMED EL CAFSI 1 1 Faculté des Sciences de Tunis, Département de Biologie, Laboratoire de Physiologie de la Nutrition, Campus Universitaire, 1060 Tunis, Tunisia 2 Institut National Agronomique de Tunisie, Département des Sciences de la Production Animale et de la Pêche, 43 Av. Charles Nicole, 1082 Tunis, Tunisia 3 Department of Genetics and Biotechnology, Center for Genetics and Biotechnology of the University of Tras-os-Montes and Alto Douro CGB/UTAD P-5000-911 Vila Real, Portugal Received: 12 September 2005 Accepted after revision: 16 March 2006 This study reports the first evidence of reproduction of Crassostrea gigas in the Bizert lagoon of Tunisia. The gametogenetic cycle of this species was examined from February 2002 to January 2003 for variation in maturation stage. Environmental parameters such as temperature, salinity, and chlorophyll a concentration were monitored. Initiation of gametogenesis took place in March when water temperature reached 14ÆC. Ripe oysters were observed in May at a water temperature of 20ÆC. Spawning began in June and reached a peak in September when water temperature ranged between 23ÆC and 27ÆC. During the latter period, oysters presented gonads with ruptured follicles and residual gametes. Spats, from 15 to 20 mm in length, were observed in November 2002 fixed under other oysters. Complementary studies have to be performed, but the present contribution could be of significance for the Tunisian oyster industry, which until now remains dependent on French spat importation. Key words: bivalve, Grassostrea gigas, gametogenetic cycle, environmental parameters, Bizert lagoon. * Corresponding author: tel.: +216 22558004, fax: +216 71885480, e-mail: salwadridi@yahoo.fr