Size at first maturity on the mussel Mytilus platensis d’Orbigny, 1842 at the Southwest Atlantic

The size at first maturity of the bivalve Mytilus platensis d’Orbigny, 1842 was estimated in the intertidal population of Villa Gesell (37° 15'S; 56° 57'W), Buenos Aires, Argentina. We hypothesize a variation in population maturity associated with shell length (SL) and differences between females and males. Individuals were analyzed histologically, sexed (females and males), and classified as mature and immature. We carried out a Kernel Density Estimation (KDE) to allow us to visualize the distribution of the classifications based on the SL and used a Generalized Linear Model (GLM) to study the size at first sexual maturity for the population and between sexes. Our results showed immature specimens with reduced development in acini and expanded connective tissue. Mature males and females showed the acini expanded and filled with vitellogenic oocytes and spermatozoa, respectively. The size at first sexual maturity at which 50% of the population was mature (SL50) was 11.80 mm SL for all population, while SL50 was 11.42 mm in females and 10.83 mm in males. We determined significant interaction between SL and sex (p < 0.05). We conclude that the knowledge of the reproductive aspects in intertidal populations is essential for the development of a potential fishing resource.