Changes in functional responses of haemocytes in the clam Tapes philippinarum from the lagoon of Venice: fishing impact and seasonal variations.

In the last few years, the Manila clam (Tapes philippinarum) has been subjected to intense fishing effort in the Lagoon of Venice owing to their commercial importance. Because of the lack of data concerning fishing-induced immunomodulation in bivalves, the consequences of fishing impact on functional responses of clam haemocytes were investigated. Clams were seasonally collected from September 2000 to July 2001 from three sites: S. Angelo, a freefishing area, and Chioggia, inside a licensed area for clam culture, in two zones characterised by fishing and nonfishing, respectively. Haematocrit, phagocytosis, Neutral Red retention time, and lysozyme and superoxide dismutase activities were evaluated. No clear fishing effect was recorded, whereas a seasonal pattern of the cell parameters analysed was revealed. Alterations in functional responses of haemocytes seem to be more closely dependent on seasonal variations in both environmental parameters and physiological status of clams than on stress caused by fishing, and they may also be related to adaptation strategies of bivalves.