Effects of Temperature on the Gastric Evacuation Rate and Maintenance Ration of Adult Pointhead Flounder Cleisthenes pinetorum

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169-day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q₁₀) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g⁻¹ day⁻¹ at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures.