1Central Research Institute of Electric Power Industry, Abiko, Chiba 270-1194, 2Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, 3Department of Applied Aquabiology, National Fisheries University, Shimonoseki, Yamaguchi 759-6595, Japan
Effects of suspended smectite (clay mineral) in seawater on the survivability of the Japanese flounder Paralichthys olivaceus were studied with an experimental apparatus that maintained solids in suspension continuously. Fish (average body weight: 4.1 g in Series I, 4.6 g in Series II) were reared for 96 h in smectite suspended seawater at the concentrations of 0, 10, 18, 32, 56, 100 g/L (Series I), and 0, 6, 10, 18, 32, 56 g/L (Series II). In the apparatus, the suspended ratio of smectite added to seawater was estimated to be more than 80% at any concentration tested. The 96 h LC50 values were estimated at 37.2 g/L (Series I) and 36.5 g/L (Series II). Particles of smectite were found among the secondary gill filaments of the dead fish, but severe lesions were not observed in the gill filaments. The primary cause of fish death was supposed to be hypoxia due to ventilation failure attributed to the blockage by smectite of the space between the secondary gill filaments.