Shell thickening in Crassostrea gigas: Organotin antifouling or sediment induced?

Abstract Crassostrea gigas spat were cultured for 8 weeks in the presence of a mixed algal diet in experimental tanks containing bis (tributyl tin) oxide (TBTO) alone, TBTO and a marine sediment, or a marine sediment alone. Growth measurements taken on a weekly basis showed enhanced weight gain in oysters exposed to nominal 50 and 100 mg l −1 concentrations of marine sediment alone. Spat in low level TBTO treatments (0.15 μg l −1 ) grew less well than the controls and showed pronounced thickening of the upper shell valve. High levels of TBTO (1.6 μg l −1 ) severely inhibited oyster growth. Tissue concentrations of TBT compounds were measured at the end of the experiment. Bio-concentration factors of 3000- and 10000-fold were demonstrated for the high and low TBTO treatments respectively.