The reproductive cycle of a Nacella (P.) deaurata population that inhabits the lower intertidal zone in Lapa-taia Bay (54°52´S; 68°29´W) was studied. Monthly samples were collected, and specimens were measured and weighed, fixing the gonads in Bouin´s fluid for histological analyses. The gonadosomatic index (GSI) was determined as a percentage of the ratio between gonadal and foot wet weight. Taking into account the presence and abundance of different cellular types, gonadal stages were established for males and females. The analyses of the variation of the gonadal stage percentages showed the first mature males and females in July. In 1989, mature females maintained a percentage higher than 30% until January. Spawning began in September and was massive in November. In 1990, the maximum percentage of mature females was found in September with all the specimens spawned in October. Nevertheless, the majority of the population was mature again in November. The male sexual cycle in 1989 showed the highest percentage of mature individuals in August, being high until October and slightly diminishing in November. The highest percentage of evacuated males was observed in November-December. In 1990, the cycle was similar to the one shown by the females, but without recovery in November. The GSI variability in males and females, and the adequate use of the GSI in determining the annual reproductive cycle were discussed. The biotic and environmental conditions that may act as a trigger for the spawning have been analyzed. |
