Effects of salinity on the clam Chamelea gallina haemocytes. Part I: alterations in immune responses.

In the present study, the eVects of diVering salinities on some important functional responses of haemocytes from the clam, Chamelea gallina, were investigated. The animals were kept for 7 days at 28‰ (hyposalinity), 34‰ (control) and 40‰ salinity (hypersalinity), and total haemocyte count (THC), haemocyte volume, phagocytosis, lysozyme-like activity (in both haemocyte lysate and cell-free haemolymph) were measured. The survival-in-air test was also performed. Clams kept at 28‰ showed signiWcantly increased THC with respect to animals kept at 34 and 40‰. The analysis of haemocyte size frequency distribution highlighted that in clams kept at 28‰ the haemocyte fraction of about 5 m in diameter and 50–100 femtolitre in volume increased markedly. Conversely, in animals kept at 40‰ an increase was observed in the haemocyte fraction having about 8–10 m diameter and 400–500 femtolitre volume. Higher phagocytic activity was recorded in haemocytes from control clams, with respect to that of clams kept at 28 and 34‰. Lysozyme-like activity in haemocyte lysate was shown to increase signiWcantly in animals kept at 28‰ with respect to that of clams kept at 40‰, whereas enzyme activity in cell-free haemolymph from clams kept at 34‰ was signiWcantly higher with respect to that of clams maintained at 40‰. A relationship between phagocytosis and lysozyme secretion is suggested. The resistance to air exposure of clams kept at 28 and 40‰ was shown to decrease signiWcantly; LT50 values fell from 7 days in clams kept at 34‰ to 4 and 5 days in those kept at 28 and 40‰, respectively. Results demonstrated that salinity values far from 34‰ aVects the functional responses of haemocytes and reduce the resistance of clams to exposure to air.