Swimming ability of bastard halibut Paralichthys olivaceus at the bottom of net cage

Abstract

Swimming speed-fatigue tests were conducted to understand the performance ability of bastard halibut Paralichthys olivaceus. In a small circular tank, a polyethylene net was set on a slant and the fish was put onto the net with its blind side facing a water current. Fish of 4.6 to 36.3 cm in total length (L) were classified into 5 size groups and fatigue time was measured at 5 water temperature ranges. Fatigue time, defined as the length of time for a caudal fin to touch the metal grating at the downstream end of the working section of the tank, was measured by the changes in the current velocity (V). Swimming ability index (SAI = (Latin small letter esh sign)03600 V·L-1 dt × 10-4) was calculated. For comparison, a fatigue test was also done on barfin flounder Verasper moseri. For bastard halibut, fatigue time was longer in higher temperatures with smaller fish having a higher performance in SAI at the same temperature. At 17°C, fatigue time was estimated over 3 hours in 1 L/s; and a few minutes in 2 L/s. Barfin flounder showed a higher performance than bastard halibut.