Reproductive cycle of Geukensia demissa (Bivalvia: Mytilidae) on a beach at Nazaret, El Moján, Zulia State, Venezuela

Abstract

The mytilid Geukensia demissa invaded Lake Maracaibo and since it is a new species at this location, little is known about its reproductive biology. We describe the reproductive cycle of this bivalve mollusk on a beach (Nazaret) located along the straight that leads into Lake Maracaibo. During 12 months (January to December), 80 specimens were collected monthly from this beach. The animals were dissected and samples of their gonadal fluid were microscopically examined to detect gametes. The different stages of gonadal development are described according to Shafee, (1989). The gonad index was calculated by the equation IG = Σ(n × V)/N. Results indicated that G. demissa presents a continuous reproductive cycle, with mature, spawning animals occurring throughout the year. Two gametogenic processes occurred, one beginning during the dry season and extending until the onset of the rainy season, and another beginning during the rainy season and extending until late November, when the animals are once again mature. Two spawning peaks were observed, one in July and the other in December; 100% spawning in the population was not observed. Synchrony was found in spawning and maturation in both male and female mussels.