1Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, 2Department of Applied Aquabiology, National Fisheries University, Shimonoseki, Yamaguchi 759-6595, 3Central Research Institute of Electric Power Industry, Abiko, Chiba 270-1194, Japan
Effects of increasing concentrations of smectite (clay mineral) in seawater on the percent utilization of oxygen (UO2) and the oxygen consumption (VO2) of the Japanese flounder Paralichthys olivaceus were investigated. Body weights of fish used were 172.0±22.8 g (experiment I) and 398.6±113.2 g (experiment II). Fish were exposed to the smectite suspended in seawater (20.2±0.4°C) with two series of concentrations: 0.0 (control), 1.0, 2.1, 4.5, 9.5, and 20.0 g L−1 (experiment I) and 0.0 (control), 31.6, and 56.2 g L−1 (experiment II). In experiment I, UO2 and VO2 of the fish exposed to the smectite were not significantly different from those of the control. In experiment II, UO2 and VO2 of the fish exposed to the smectite decreased to significantly lower values (p<0.05 in 31.6 g L−1 and p<0.01 in 56.2 g L−1 solutions) than those of the control. The primary cause of decreases in UO2 and VO2 should be the ventilation failure attributed to the blockage by smectite of the space between the secondary gill filaments. The viscosity of seawater containing 31.6 g L−1 or more smectite became considerably higher (2.4±0.0 mPa s or more) than that of the seawater used (1.2±0.0 mPa s). The increase in viscosity would force the fish to consume more energy for respiration.