The reproductive cycle,condition index and biochemical composition of the horse-bearded mussel Modiolus barbatus

The horse-bearded mussel Modiolus barbatus (Linneus, 1758) is an important edible bivalve in the Adriatic Sea; its population is especially large in the Mali Ston Bay area, where the species is present at depths up to 8 m. In order to assess the sustainable exploitation rate for this species, as well as to estimate its potential capacity for a sustainable aquaculture production, we determined the species’ reproductive cycle along with its nutrient storage strategy, employing histological and biochemical methods. The population shows significantly more females than males, and no hermaphrodites. The smallest adult individual, an active male, was 16.0 mm in length, suggesting that sexual maturation starts around this length. While the period between January and February is characterized by sexual repose, early and late stages of gametogenesis were found between March and May, and spawning peaked from June till August. The increase of oocyte diameter followed the same trend. A significant positive correlation was observed between gonad index and temperature, and a negative correlation between gonad index and salinity. Oscillations of stored nutrients were tightly coupled with the gametogenic cycle.