1Central Research Institute of Electric Power Industry, Abiko, Chiba 270-1194, 2Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan
The effects of clay mineral suspension in seawater on the survivability of Japanese flounder Paralichthys olivaceus were examined with four kinds of clay mineral products, A, B, C and D. The main clay mineral contents analyzed by X-ray diffraction were pyrophyllite in product A, kaolinite and pyrophyllite in B, sericite in C, and smectite in D. Fish (6 cm in total length) were kept for 96 hours in the suspension with products A, B and C added directly to seawater as powder. The 96 hours lethal concentration (96 h LC50) of products A, B and C were 44, 5 and 80 g/L, respectively. Similarly, 96 h LC50 values were also examined with products A, C and D added to seawater as fivefold concentrated suspension in freshwater. The 96 h LC50 values were 78, 179 and 4 g/L for products A, C and D, respectively. The 96 h LC50 value of product D was 37 g/L when it was added as powder in the former study, and was lower when added as fresh water suspension. However, the opposite results were obtained with A and C. This study indicates that the lethal effects of suspended clay mineral on marine fish depend on its composition and on the way it is added to seawater.