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Reproductive cycle of the southern geoduck clam, Panopea abbreviata (Bivalvia: Hiatellidae), in north Patagonia, Argentina

Summary On the basis of histological examination, we present the first description of gametogenesis in Panopea abbreviata. Six stages of gonad development were identified using morphological and histochemical criteria. The gonads are diffuse and cannot be sexed with the naked eye. The analyses of gonad tissues showed that the gametogenic cycle is continuous with no resting period. Ripe individuals of both sexes were found for most of the year, and the spawning season seems to be protracted. The application of histological techniques to individuals collected monthly revealed a bias in the sex ratio depending on the body length. Even when the sex ratio was balanced in large clams, for small individuals, the sex ratio was biased in favour of the males. Although no hermaphroditic individuals were found in our samples, the possibility of protandry should be examined further.