Reproductive cycle and biochemical composition of Hexaplex trunculus (Gastropoda: Muricidae) from Bizerte lagoon, northern Tunisia

摘要

ABSTRACT: This study investigates the reproductive cycle, size at first sexual maturity and biochemical composition of Hexaplex trunculus from the Bizerte lagoon (northern Tunisia). Overall, females predominated over males, resulting in an unbalanced sex ratio of 1.2:1. Males dominated in the smaller size classes (40 mm shell length, SL), sex ratios were balanced at the 40 to 50 mm SL range, and females dominated in the larger size classes (50 mm SL). The gonad developmental stages and the gonadosomatic index (GSI) indicated that H. trunculus apparently has an annual reproductive cycle with extended periods of gonadal activity. In both sexes, examination of the appearance of the gonads showed that gamete release occurred mainly from March to May (with an apparent spawning between March and April), followed by a period of empty gonads between June and August. Sexual maturity occurred at smaller sizes in males (SL₅₀ = 41.02 mm SL) than in females (SL₅₀ = 50.47 mm SL). The contents of protein, lipids and carbohydrates were invariably greater in the gonads than in the foot, confirming the key role of the reproductive tissues in energetic storage. The monthly variation in protein, lipids and carbohydrates in the gonads followed the oscillation in the relative proportion of developed gonads and in the GSI, reflecting energetic mobilisation during maturation and spawning. Overall, the data gathered in this study constitutes valuable baseline information for making preliminary recommendations to the fishing community targeting H. trunculus in the Bizerte lagoon. Further studies and more solid data on the reproductive cycle of the species are required before definitive management measures for this locally important artisanal fishery can be proposed.