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

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 (SL 50 = 41.02 mm SL) than in females (SL 50 = 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. KEY WORDS: Reproductive cycle · Spawning season · Size at sexual maturity · Biochemical composition · Fisheries management · Hexaplex trunculus · Muricidae · Bizerte lagoon Resale or republication not permitted without written consent of the publisherAquat Biol 10: 155-166, 2010 156 the Atlantic is mainly restricted to the coasts of Portugal and Morocco, and the Madeira and Canary archipelagos (Poppe & Goto 1991, Houart 2001). This species is harvested for human consumption and has commercial value in several Mediterranean countries such as Spain, Italy, Croatia, Cyprus and Turkey (Fischer et al. 1987), as well as along the Atlantic coasts of Spain (mainly in Andalusia) (Anon 2001) and Portugal (mainly in Algarve) (Vasconcelos et al. 2008a). In the Bizerte lagoon (northern Tunisia), the banded murex is the target species of an artisanal fishery using baited traps, but is also a bycatch species in fishing nets (Gharsallah et al. 2004). The banded murex constitutes a locally important fishing resource in the Bizerte lagoon, with estimated monthly catches of ~1.8 tons between 1999 (I. H. Gharsallah unpubl. data), but the fishery lacks specific regulations (e.g. minimum landing size, closed seasons in fishing activity).While some studies on the reproductive biology an...

Reproductive cycle of Bolinus brandaris (Gastropoda: Muricidae) in the Gulf of Gabès (southern Tunisia)

“…This finding agrees with other studies conducted on this species along the Catalan coast (northeastern Spain) (Ramón & Amor, 2001 and in the Ria Formosa lagoon (southern Portugal) , being also commonly observed in another muricid gastropod (the banded murex, Hexaplex trunculus) caught along the Tunisian coast (e.g. Elhasni et al, 2010;Gharsallah et al, 2010). In the present study, female-biased sex ratios occurred mainly between April and August, but with a clear period of highly unbalanced sex ratios from April to June, coinciding with the breeding and spawning season of B. brandaris locally.…”

“…Indeed, if during bottom trawling a breeding aggregation is caught by the trawl path, most likely females will predominate in the catches and generate strongly female-biased sex ratios. A similar predominance of females over males also occurred during the breeding and spawning season of H. trunculus in Tunisian waters (Elhasni et al, 2010;Gharsallah et al, 2010). In the present study, while sex ratios were balanced in the smallest size classes (< 50 mm SL), the proportion of females in the samples augmented by increasing specimen size, generating female-biased sex ratios in the largest size-classes (> 50 mm SL).…”

“…Therefore, individuals were classified according to a macroscopic scale based on gonad size and appearance, and also on the development of secondary sexual characters in both sexes (a vesicula seminalis in males, a capsule gland in females) ( Table 2). An identical approach was recently adopted with success in studies concerning the sympatric muricid H. trunculus (Elhasni et al, 2010;Gharsallah et al, 2010).…”

Relative growth and reproductive cycle in two populations of Bolinus brandaris (Gastropoda: Muricidae) from northern Tunisia (Bizerta Lagoon and small Gulf of Tunis)

“…In fact, Lahbib et al (2009) registered only one period in both sexes between January and May-June. Gharsallah et al (2010) reported that in both sexes of H. trunculus, gamete release occurred mainly from March to May (with a spawning peak between March and April), followed by a period of empty gonads between June and August. Moreover, another study on the reproductive cycle of H. trunculus from the Gulf of Gabès detected just one period of gametic emission in both sexes (January-May for males and April-May for females) (Elhasni et al 2010).…”

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“…Previous studies focusing on H. trunculus have been based on sexual abnormality known as imposex and reproductive biology (e.g., Axiak et al, 1995;Gharsallah et al, 2010;Terlizzi et al, 1998;Lahbib et al, 2008;Lahbib et al, 2010). Nevertheless, the knowledge of fishing effort and stock structure of this species, which occurs in a large distribution range with different environmental conditions, is still very limited.…”