Ciclo gonadal del chorito Mytilus chilensis (Bivalvia: Mytilidae) en dos localidades del sur de Chile

A qualitative and quantitative analysis was carried out of the gonadal cycle of the bivalve Mytilus chilensis from Chaihuín and Yal bay, southern Chile, between October 2007 and June 2008. Four gametogenic stages were determined using histological analysis of the gonads, and quantitative estimates were made of the Gametic Volume Fraction (VFG), percentage of inter follicular connective tissue, and the Gonadosomatic Index (IG). The quantitative analysis (VFG) was the best indicator of spawning. Two spawning events, one in October and one in March, were observed simultaneously in both sexes of mussels from Chaihuín. However, for specimens from bahía Yal, four spawning events were registered, principally from March to June (autumn), when the water temperature decreased. The relationship between the IG and the gametogenic stages was very low, as was that between the IG and the percentage of mature oocytes. Therefore, the IG is not a good indicator of spawning in this species. A re-evaluation of the ban period established for Mytilus chilensis (1 November to 31 December) is suggested since most individuals from the populations studied mature mainly in October. At both sites, the percentage of connective tissue for the analyzed mussel individuals ranged between 15 and 70% of gonadal coverage. The results obtained in the present study showed differences in the reproductive cycles of Mytilus chilensis between the sites sampled. These differences could be due to environmental differences (e.g. temperature) caused by the latitudinal gradient.