Morphometric relationships and relative growth of Hexaplex trunculus and Bolinus brandaris (Gastropoda: Muricidae) from the Ria Formosa lagoon (southern Portugal)

The present study reports morphometric relationships and discusses the relative growth in the banded murex (Hexaplex trunculus) and the purple dye murex (Bolinus brandaris) from the Ria Formosa lagoon (southern Portugal). A total of 11 morphometric parameters (eight linear variables: shell length, shell width, total aperture length, aperture length, aperture width, spire length, spire width and siphonal canal length; three ponderal variables: total weight, soft parts weight and shell weight) were analysed in both species. The analyses comprised numerous individuals of both sexes and with broad size ranges (H. trunculus: 10.7–82.8 mm shell length; B. brandaris: 14.6–107.7 mm shell length), fairly representative of the populations from the Ria Formosa lagoon. In general, B. brandaris exhibited greater morphological plasticity and higher variability in shell shape compared with H. trunculus. In both species, the vast majority of morphometric relationships displayed positive allometries, distantly followed by negative allometries and by isometries. Although H. trunculus and B. brandaris are known to lack external sexual dimorphism, several morphometric relationships revealed significant differences in the type of growth between sexes, which should be further confirmed using more powerful techniques, such as geometric morphometric analyses of shell shape.

A Natural and Concurrent Interferent in Bolinus brandaris with Consequences on Amnesic Shellfish Poisoning Risk Management

Regulations aimed to protect public health from amnesic shellfish poisoning (ASP) are focused on the detection and accurate quantification of domoic acid(DA). The reference detection determination used by the different shellfish safety monitoring agencies worldwide is HPLC separation followed by UV detection, in which different chromatographic column lengths or brands are accepted as long as it is C18 column. A laboratory validation of this method showed different performance of two accepted chromatographic columns when analyzing Bolinus brandaris samples. A natural compound, present only in those samples that contained DA, was evidencedby one of the columns. The DA quantification obtained with the column that coelutes both compounds was approximately twice the amount obtained with the column that separates them. This difference has important consequences in the ASP toxins management for thisfishery. The identity and toxicity of the compound are still unknown.

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

The reproductive cycle of the purple dye murex (Bolinus brandaris) from the Gulf of Gabès was studied through gonad histology and calculation of bio-physiological indices (general condition index - K and gonadosomatic index - GSI). The shell length at first sexual maturity (SL50) of B. brandaris was also investigated using a macroscopic maturation scale. The population sex ratio was statistically unbalanced (M:F = 1:1.5), with a significant dominance of females. Monthly variation in gonad maturation stages, K and GSI revealed that B. brandaris has an annual reproductive cycle, long period of gonadal activity and slight asynchrony between sexes. The spawning season extended between April and July, with a clear spawning peak from May to June. The SL50 was reached at 56.4 mm in females and 54.6 mm in males. At present, B. brandaris has no commercial value in Tunisia, but it is predictable that it will become a fishery-exploited species in the near future. The present data, particularly the timing of spawning season and the size at first sexual maturity, constitute baseline information for the proposal of fishery management measures, aiming to ensure sustainable exploitation and long-term preservation of this alternative fishing resource.

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

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.