Document Type : Original Article
Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 1551-8 Taira-machi, Nagasaki, 851-2213, Japan
National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries Research and Education Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, 739-0452, Japan
Survival time of juvenile pen shell Atrina pectinata (shell length ≈ 34 mm) exposed to hyposaline water without sediments was investigated in laboratory experiments. The bivalves were individually maintained in rearing cups in which salinity was decreased either gradually (over 1–11 h to 12 salinities ranging from 0 to ca. 34 ppt) or rapidly (directly to 21 salinities) at 12 and 24 °C. When the environmental salinity was gradually decreased, survival time differed markedly between the bivalves exposed to: salinities ≤ 18.6 ppt (survival time < 20 h in general) vs. ≥ 21.1 ppt (> 83 h) at 24 °C; and between salinities ≤ 15.1 ppt (< 34 h) vs. ≥ 17.2 ppt (> 83 h) at 12 °C. When the environmental salinity was rapidly decreased, survival time, again, differed markedly between the bivalves exposed to: salinities ≤ 15.9 ppt (< 20 h in general) vs. ≥ 17.7 ppt (> 140 h) at 24 °C; and salinities ≤ 21.3 ppt (< 38 h in general) vs. ≥ 22.3 ppt (> 140 h) at 12 °C. Such sharp decreases in survival time due to reduced salinity led to the selected, statistical models that assume either a sharp exponential increase or stepwise hike in hazard (instantaneous mortality rate) according to salinity reduction. These data and models indicate that juvenile A. pectinata should not be kept at salinities < 21 ppt for periods > 1 day in environments without sediments.