Conspecific comparison on the effects of abiotic conditions on the swimming and metabolic performance of Pacific chub mackerel (Scomber japonicus) among stocks distributed in different area

Pacific chub mackerel (Scomber japonicus) is a small pelagic fish species widely distributed throughout the coastal areas of Pacific. To explore the potential differences in the effects of abiotic conditions (e.g., temperature, current speed) on swimming performance and metabolism of Pacific chub mackerel among stocks distributed in different area, swimming energetic and metabolic data of the wild-caught Northwestern stock were measured under various temperatures (18°C and 24°C) using a variable-speed swim-tunnel respirometer. Then these data were further parameterized and compared with the previous findings from the wild-caught Northeastern Pacific stock measured under same temperatures, as well as the aquaculture-reared Northwestern stock measured at 18°C and 14°C. For the wild-caught Northwestern stock, the maximum sustainable swimming speeds (U_max) was 38-85 cm s^-1 for 12.6 – 14.9 cm individuals, and showed no significant difference between 18°C and 24°C. At the same temperature of 18°C, within the size range of wild-caught Northwestern stock, aquaculture-reared Northwestern stock and wild-caught Northeastern stock showed no significant increase in U_max , suggesting no significant difference on the swimming ability among these stocks. Meanwhile, the mass-specific oxygen consumption rate (M_O2) of wild-caught Northwestern stock increased exponentially with swimming speed (U, in cm s^-1) with same increase rate of aquaculture-reared Northwestern stock and wild-caught Northeastern stock. At a given speed and fish mass, M_O2 increased with temperature. these was consistent with previous studies of Northeastern stocks, while the temperature dependency of M_O2 of Northwest stock is significantly lower than eastern stock. This indicated that the Northwestern stock was less sensitive for temperature on metabolism, which may related to a wider migration area of Northwestern stock and more variated environment in Kuroshio region compare to the California current.