SWIMMING ABILITY OF JUVENILE TIGER PUFFER, TAKIFUGU RUBRIPES WITH DIFFERENT BODY MASSES AND STARVATION LEVELS

The tiger puffer, Takifugu rubripes, which distribute in the East China sea, Yellow sea and Bohai sea, is an important fish species in aquaculture and stock enhancement in China. Due to the higher fishing pressure, catches of wild tiger puffer decreased significantly in the late 1980s. Aquaculture-based fisheries enhancement involves the release of cultured organisms to enhance, conserve, or restore fisheries. To restore the stock of tiger puffer, China, Korea and Japan began to release this species. High mortalities in stock enhancement have been found in many species after release due to predation and starvation. Swimming ability directly affects the capacity of finding food, escaping from predators, maintaining position, schooling and migration in released fish. In this study, we investigated the effects of body mass and starvation on the swimming ability of juvenile tiger puffer. The critical swimming speed (U_crit, cm/s), preferred swimming speed (U_pref, cm/s), percentage of accumulated time (P_t, %) under six flow velocities (2—36 cm/s), average flow velocity of preferred zone (V_mean, cm/s) and total swimming distance (D_1h, m) of juvenile tiger puffer was determined under different body masses (0.22—3.31 g) and starvation days (1d, 3d, 6d and 9d). Body mass and starvation significantly affected the U_crit, P_t, V_mean and D_1h of juvenile tiger puffer. The U_crit, U_pref, V_mean and D_1h increased from 10.17 cm/s, 2—5 cm/s, 3.79 cm/s and 139.06 m to 17.13 cm/s, 13—26 cm/s, 16.51 cm/s and 580.03 m, respectively, as the body mass increased, whereas the relative U_crit (U_crit’, body length/s, BL/s) decreased from 5.83 to 3.56 BL/s. The relationship between body mass and U_crit, U_crit’, P_t, V_mean and D_1h can be described by the quadratic model. The U_crit, U_crit’, U_pref, V_mean and D_1h decreased from 16.47 cm/s, 3.38 BL/s, 13—26 cm/s, 15.45 cm/s and 566.18 m to 10.03 cm/s, 1.98 BL/s, 2 cm/s, 2.83 cm/s and 119.74 m, respectively, as the starvation day increased. The relationship between starvation day and U_crit, U_crit’, P_t, V_mean and D_1h can be described by the quadratic model. The U_crit increased as the body mass increased, which might be due to the increase in muscle mass and efficiency, available energy stores and metabolic capacity with size. Compared to larger conspecifics, the cardiorespiratory system of small fish is more efficient because they have relatively larger respiratory and circulatory organs. The maximum metabolic rate (MMR) decreased as the body mass increased in fish, which might lead to the decrease in U_crit’. The stronger the swimming ability of the released fish, the higher the survival rate. As the swimming ability of juvenile tiger puffer increased with the body mass, we suggested that the release size should above 5 cm. In order to prevent the released tiger puffer from being flushed away by the current or swimming against the current constantly, the current velocity of the releasing area should below 20 cm/s. The swimming ability of juvenile tiger puffer decreased with the starvation days, which might be due to the decrease in muscle enzyme activity, metabolic capacity and available energy for swimming under starvation. The reduction in the swimming ability might weaken the predation and anti-predation capacity of the released tiger puffer. Results can be of value in understanding ecological processes and improving the stock enhancement of tiger puffer.