A study of gonadal development in Ruditapes decussatus (L.) (Mollusca, Bivalvia), using image analysis techniques: Influence of food ration and energy balance

摘要

This study evaluated the influence of food availability on sexual maturation in Ruditapes decussatus (L.) in conditions of positive (daily rations of 0.10, 0.24, 0.42, and 0.96%), zero (0.05% ration), and negative energy balance (0.025% ration). The percentages correspond to the organic weight of the phytoplankton supplied as a proportion of the live weight of the clams. The gonadal occupation index (GOI) and the percentage of ripe oocytes in the gonad, calculated using image analysis techniques, were taken as indicators of the degree of sexual maturity. Gonadal development in R. decussatus occurred under all food rations and energy balance conditions, even when the organic weight of the clams decreased during the period of sexual development. All conditions registered a gradual increase in GOI and the percentage of ripe oocytes throughout the experimental period. Maximum values for GOI varied between 30% and 40% in females and between 55% and 75% in males, according to the amount of food available. Similarly, mature sexual cells were observed under all experimental conditions, with maximum percentages in females of between 30% and 40%. The extent of gonadal development is directly related to the amount of food available, which in turn has a direct bearing on the rate of gonadal development, with smaller rations leading to a lower rate of increase in the gonadal occupation index and the percentage of ripe oocytes.