Spatial and annual distribution of age structure in the Tunisian populations of European clams Venerupis decussata

This study was carried out on the natural populations of Venerupis decussata from two Tunisian lagoons (North and Boughrara). Dynamics and morphological structures, growth and age characteristics of these clams were determined. Additionally, condition (CI) and gonadic (GI) indices were monthly determined from both populations. These indices were used as a tool in the determination of the harvesting period of this species which seems to be linked to the spring season. Our data showed that the dominant length ranged from 28.96 to 37.18 mm, while weight ranged from 17.91 to 20.98 and width ranged from 4.56 to 5.59 for both populations collected, respectively, from North Lagoon and Boughrara Lagoon. The morphological relationships indicated hypoallometry and hyperallometry between weight (2.347 ≤ b ≤ 2.816) and length (0.644 ≤ b ≤ 0.912), respectively. The marginal examination implied that only one growth increment was formed per year mainly during the summer season. The age class ranged from one to sixth with the dominance of the five age groups in the population of Boughrara as compared to the North Lagoon population, which reached the sixth age group. According to our results, the von Bertalanffy growth parameters were assumed and estimated to K 0.3 and 0.4 year −1 and L∞ 41 and 37.09 mm for the North and Boughrara populations, respectively. Furthermore, the growth performance index (Φ), age precision examination (IAPE), coefficient of age variation (CV) and annual growth rate (Gx) were assessed revealing that North population has a better growth rate as compared to the Boughrara one.