Relative Growth and Reproduction in Tunisian Populations ofHexaplex trunculuswith Contrasting Imposex Levels

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

“…These results confirm previous findings by Vasconcelos et al (2008b), who reported that biophysiological indices (especially GAI and CGI) constitute simple, practical and efficient indices for the routine assessment of reproductive activity. B. brandaris showed the same timing of ovary and testis development in both sexes, which were similar to B. brandaris caught in the Ria Formosa lagoon (southern Portugal) (Vasconcelos et al 2011) and to H. trunculus collected from the Bizerta Lagoon (Lahbib et al 2009), but distinct to those observed in the population from the Spanish coast (Ramón & Amor 2002). The annual cycle started with early maturation stages in September-October, afterwards the frequency of more developed maturation stages increased until March and April preceding small emission periods in MA and CB, respectively.…”

“…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.…”

“…Indeed, in Italian populations of H. trunculus, Terlizzi et al (1999) reported that those with advanced imposex stages have greater shell length and width, compared with normal and partially affected populations. In the same species, Trigui El Menif et al (2006) and Lahbib et al (2009) showed that individuals collected from Menzel Jemil (low incidence of imposex) grew more in terms of soft body weight and shell aperture, whereas gastropods from Bizerta Channel (high incidence of imposex) grew more in terms of shell weight. The present data corroborates these later findings, but contradict those of Terlizzi et al (1999) concerning shell length and width.…”

“…However, this is just a hypothesis, because these values measured in situ at the time of sampling might not accurately reflect the real monthly variation in seawater temperature in both collecting sites. Lahbib et al (2009) associated the asynchrony in the reproductive cycle between two populations of H. trunculus to differences in seawater temperature, which showed deviations above 2…”

“…In H. trunculus from the Bizerta Channel, Lahbib et al (2009) showed that advanced imposex stages and sterile females could have influenced the GAI because the gonad did not show normal development. The capsule gland index (CGI) of B. brandaris from the two sampling sites displayed the same general trend of the remaining bio-physiological indices.…”