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

Abstract

A study on the relative growth and reproductive cycle of the purple dye murex (Bolinus brandaris) was performed from March 2007 to February 2008 in two populations with contrasting imposex levels (Carthage Byrsa -CB in the small Gulf of Tunis and Menzel Abderrahmane -MA in the Bizerta Lagoon). Both populations presented balanced sex ratios. Comparison of allometric relationships established between linear and ponderal variables (sexes confounded) revealed higher growth in CB than in MA. Mature individuals were found throughout the year, except for September in MA. Spawning periods occurred from March-April to May and from June to August in both sites. Spawning was associated to an increase in seawater temperature. Besides increasing the current knowledge on the biology of B. brandaris from the southern Mediterranean, the information gathered in the present study constitutes a useful baseline for the sustainable management of local wild stocks, namely by prohibiting collection of snails during the spawning season.

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“…While GAIA and GIB suggest the most consistent trends according to the seasonality of the complete reproductive cycle. Also GAIA is accurate enough to reveal changes related to spawning and partial spawning in Bolinus brandaris and Haliotis rubra (Abidli et al, 2012;Litaay and De Silva, 2002). And the efficiency of GIB as an indicator of gonadal maturation also has been demonstrated in H. cracherodii and H. rufescens (Boolootian, 1962;Ault, In addition to GAIA and GIB, there are other reproductive indices that are calculated based on variables measured in cross-sections and other biometric data (Ault, 1985;Capinpin, 1998;Litaay and De Silva, 2002;Setyono, 2006;Abidli et al, 2012).…”

“…Reproductive indices.-Reproductive indices provide indirect information that allows to evaluate the reproductive condition, and are commonly used as tools to evaluate gonadal development and determine the timing of reproductive activity (Boolootian et al, 1962;Litaay and De Silva, 2002;Morais et al, 2003;Najmudeen and Victor, 2004;Najmudeen, 2007;Abidli et al, 2012;Elhasni et al, 2013). Usually, a drastic decrease in a reproductive index is interpreted as spawning occurrence (Boolotian et al, 1962).…”

“…Nutritional indices.-Nutritional indices have been used to assess the nutritional status of fish (Bolger and Connolly, 1989), bivalve molluscs (Crosby and Gale, 1990;Angel-Pérez et al, 2007) and gastropods (Zetina et al, 2000;Abidli et al, 2012), among others. In gastropods, the condition index has been used to evaluate the condition of Melongena corona (Zetina et al, 2000) and Bolinus brandaris (Abidli et al, 2012) in relation to the reproductive cycle, since it is deemed a good indicator of the maturity state because of the use of muscle and digestive gland reserves in gametogenesis (Webber and Giese, 1969).…”

“…The gonadic index was estimated as defined by Abidli et al (2012), but using tissue fresh weight instead of dry weight (GI, Table 1). The gonadic index of calculated mass was estimated to express the proportion of HGGW with respect to Wmc (MGI, Table 1).…”

“…In haliotids, these indices have been used primarily to evaluate the reproductive status of populations (Boolootian et al, 1962;Webber and Giese, 1969;Poore, 1973;Ault, 1985;Capinpin et al, 1998;Counihan et al, 2001;Litaay and De Silva, 2002;Najmudeen and Victor, 2004;Setyono, 2006). The simplest indicator is calculated by dividing the gonad weight by the total weight of the body, and it is commonly used in haliotids (Setyono, 2006) and other gastropods (Zetina et al, 2000;Morais et al, 2003;Abidli et al, 2012). The indices most commonly used are those that evaluate gonadal maturity based on the cross-sectional area occupied by the hepatic glandgonad complex (HGGC) in relation to either total shell length (Boolootian et al, 1962;Gurney and Mundy, 2004) or total area (Newman, 1967).…”