Effects of hydrogen sulfide on the feeding activity of Manila clam Ruditapes philippinarum

After being exposed to anoxia for 24 h, with and without hydrogen sulfide (H(2)S; 5 or 30 mg l(-1)), the feeding activities of the Manila clam Ruditapes philippinarum were examined in the laboratory under normoxic conditions. The clearance rates of clams after exposure to anoxia with 30 mg l(-1) H(2)S (5.1 l h(-1) ind.(-1)) were significantly lower than in those exposed to normoxic or anoxic conditions (11.4 or 11.2 l h(-1) ind.(-1), respectively). The phytopigment concentration of the digestive glands of clams treated with 30 mg l(-1) H(2)S under anoxic conditions (41.7 mu g g(-1), wet weight of digestive gland) was significantly lower than that measured in other experimental treatments in this study (548.4 mu g g(-)1 for normoxia, 461.9 mu g g(-1) for anoxia only, 479.8 mu g g(-1) for 5 mg l(-1) sulfidic anoxia; p < 0.01). Histological examination of clam tissue revealed that the ciliary epithelium was damaged by a high concentration of H(2)S. These findings indicate that once the clams suffered damage to their gills by exposure to H(2)S, their feeding activity was impaired and they could not ingest prey, even when their environment was returned to optimal conditions.