Experimental data on growth, mortality and reproduction of Ostrea edulis (L., 1758) in a semi-enclosed basin of the Mediterranean Sea

Biometry, growth, survival and mortality rates as well as reproduction of O. edulis have been evaluated in the Taranto Sea, a semi-enclosed basin of the North-Western Ionian Sea (Mediterranean Sea). A crossed experimental design with 3 factors (container, depth and stocking density) was defined to investigate their effect on the sizes, growth performance, survival and mortality rates. Moreover, the reproduction was studied to better understand the life cycle of the species in the basin. The investigated experimental conditions caused significant differences in both size changes and growth parameters. In particular, the density was the main factor influencing both biometry and growth. The oysters cultivated at low density showed L∞ (155.46±46.38mm DVL), k (0.42±0.25year⁻¹) and Φ′ (2.00) values significantly higher than those reared at high density L∞ (134.28±36.13mm DVL), k (0.35±0.22year⁻¹) and Φ′ (1.80). The winter point (WP) occurred during winter and the strength of the seasonal oscillation (C) ranged between 0.10 and 0.37. No significant differences between the experimental rearing conditions were observed in either survival (S) or mortality (Z) rates. Oysters reared at low and high density showed mean S values equal to 0.88±0.03 and 0.89±0.03, respectively as well as mean Z values equal to 0.13±0.03 and 0.12±0.04. Maturation of gonads occurred continuously during the year showing a slackening during summer when the highest temperatures were recorded in the water column. In addition, the highest percentages of fluent gonads were observed during winter. Histological analysis confirmed the macroscopic observation of gonads. In particular, gamete differentiation was observed during late autumn and early winter. An inverse correlation between the condition index and the mean temperature in the water column was observed throughout the study period. The present results indicate an optimal crop age of about 2years, corresponding to the commercial size of 8-9cm dorsal-ventral length and weight of 55-60g.