FLOW VELOCITY EFFECTS ON SWIMMING BEHAVIOR AND EXERCISE PHYSIOLOGY OF JUVENILE ACANTHOPAGRUS SCHLEGELII

Acanthopagrus schlegelii is an important fish species for enhancement and release in Chinese coastal waters. To study its swimming behavior and exercise physiology can provide technical support for the offshore cage culture and the feralization train of the enhancement and release. In this study, the swimming behavior (induced velocity, critical swimming speed, burst swimming speed and tail beat frequency), respiratory metabolism (oxygen consumption rate (Mo₂), cost of transport (COT), median survival time and suffocation point), physiology and biochemistry (lactate, glycogen, glucose, phosphocreatine and hydrocortisone) of juvenile Acanthopagrus schlegelii body length of (12.38±0.69) cm, weight of (45.99±9.05) g at 19℃ and different flow velocities were measured in a loop test flume produced by Loligo Systems in Denmark. The results showed that the relative induced velocity of juvenile Acanthopagrus schlegelii was about 1.42 BL/s (body length/s), the critical swimming speed was about 76 cm/s, and the burst swimming speed was about 114 cm/s. The tail beat frequency had a significant linear positive correlation with the flow velocity. The standard metabolic rate was about 332.25 mg/(kg·h), and the activity metabolic rate had a quadratic polynomial relationship with the flow rate. The lowest oxygen consumption rate appeared at the flow rate of 3.6 BL/s, which was about 185.65 mg/(kg·h). The cost of transport had a power function relationship with the flow rate, and the minimum cost of transport appeared at a flow rate of 4 BL/s, which was about 66% U_crit flow rate. The shortest median survival time of juvenile Acanthopagrus schlegelii was in the still water with about 3hours, and the longest median survival time was under the low (1 BL/s) and medium (3 BL/s) flow rates with more than 10h. Suffocation point was about 0.34 mg/L in the still water, 1.70 mg/L at the low and medium flow rates, and about 3.18 mg/L at high flow rate. The contents of glycogen and phosphocreatine in white muscle and liver were higher at the low and medium flow rates (20% U_crit, 50% U_crit). The level of blood lactate was higher in the still water and at high flow rate, which correlated with oxygen consumption rate, suffocation point change trend was consistent. In conclusion, it is recommended that the flow rate for cage culture of juvenile Acanthopagrus schlegelii should not exceed 0.8 m/s, the appropriate training flow rate should be within the range of 1.5—3.5 BL/s, and the acclimation time should be more than 2 weeks.