SEASONAL-VARIATIONS OF METALLOTHIONEIN CONCENTRATIONS IN THE ASIATIC CLAM (CORBICULA-FLUMINEA)

Natural variations of metallothionein (MT) concentrations in the Asiat ic clam Corbicula flaminea were analyzed over a 1-year period in speci mens collected from an unpolluted site (Cazaux-Sanguinet lake, southwe st France). Sampling was carried out from November 1994 to December 19 95, one to three times per month, according to the season. At each sam pling time, lake temperature was measured and concentrations of MTs, C d, Hg, Zn and Cu were determined in the whole soft body and in four or gans or tissue samples. A histological study was conducted simultaneou sly to follow the development of the gonads in relation to the reprodu ctive cycle of this bivalve. Results showed very high fluctuations in MT concentrations over the whole year, with a maximum value measured i n the middle of May and ratios of around 4 at the whole organism level between extreme MT values. The tissue compartment presenting the most important variations was the visceral mass, which contains the gonads . Metal accumulation in the organisms did not seem to be involved amon g the factors likely to account for these variations in MT concentrati ons; metal concentrations remained at low and relatively constant leve ls throughout the whole year. The histological study revealed one spaw ning period from late May to the middle of June, appearing just after the MT ''peak,'' with maximum incubation of the embryos in the gills i n late June. Because MT biosynthesis can be induced by hormonal secret ions implicated during reproductive phenomena, the variations in MT co ncentrations appeared to be directly related to the biological cycle o f this freshwater mollusc rather than to the direct or indirect effect s of metal bioaccumulation. (C) 1997 Elsevier Science Inc.