REPRODUCTIVE CYCLE OF THE CARPET SHELL CLAM Ruditapes decussatus (LINNAEUS 1758) IN ARAXOS LAGOON (NW PELOPONNISOS, GREECE) AND IN EVINOS ESTUARY (SOUTH AITOLOAKARNANIA, GREECE)

摘要

The reproductive cycle of two natural populations of the carpet-shell clam Ruditapes decussatus, in Araxos lagoon and in Evinos estuary, were determined by monthly examination of gonads from November 2000 to October 2001. The histological examination showed that in Araxos lagoon individuals were in the inactive stage from November to January, when gonadal development first took place. Ripe individuals appeared in April and the spawning activity begun in June and continued increasingly until October. The redevelopmental stage lasted from July to September and the duration of the completely spawned stage was from June to October. In Evinos estuary, the inactive stage took place from November to June. In some individuals gonadal development began in January and ripe individuals appeared in May. The spawning stage lasted from July to October, the redevelopmental stage appeared only in August and the completely spawned stage took place from August to September. The clams did not show any sign of hermaphroditism. The percentage of females was 57.5% in Araxos lagoon and 60% in Evinos estuary. The clams in Araxos lagoon had a more intense spawning activity, while clams in Evinos estuary stayed significantly longer in the inactive stage. The condition index presented a higher mean value and lower variability in Araxos lagoon than in Evinos estuary.