| The farmed Thamnaconus septentrionalis were taken as the research object in this article,The main research results of swimming and respiration metabolism of Thamnaconus septentrionalis are as follows:1.The effect of flow rate on swimming movement of juvenile Thamnaconus septentrionalis was studied by self-made fish swimming device.The results showed that:(1)at 16℃water temperature,the critical swimming speed(U_C)of four body weight specifications was 0.42±0.03m/s at 10g,0.47±0.01m/s at 15g,0.53±0.03m/s at20g and 0.62±0.01m/s at 25g.Burst swimming speed(U_B)was 0.53±0.06m/s at 10g,0.56±0.02m/s at 15g,0.60±0.02m/s at 20g,0.72±0.01m/s at 25g,The critical swimming speed(U_C)and burst swimming speed(U_B)of juvenile Thamnaconus septentrionalis were significantly increased with body weight increasing(P<0.05).(2)The critical swimming speed(U_C)and burst swimming speed(UB)of 25g fish were measured at12℃,16℃,20℃,24℃and 28℃.The results showed that the critical swimming speed(U_C)and burst swimming speed(U_B)increased firstly and then decreased with the increase of temperature.There was no significant difference in critical swimming speed(U_C)between 16℃,20℃and 28℃groups(P>0.05),and no significant difference between 20℃and 24℃.The critical swimming speed(U_C)reached the maximum value at 24℃,and the burst swimming speed(U_B)had no significant difference between 16℃,20℃and 28℃.There was no significant difference between the 20℃group and the adjacent 24℃and 16℃groups(P>0.05),but the burst swimming velocity(U_B)reached the maximum value at 24℃and was significantly different from other groups(P<0.05).(3)The caudal fin,dorsal fin and anal fin and the trend rate were measured at the flow rates of 0.009m/s,0.12m/s,0.24m/s,0.36m/s and 0.48m/s in the still water group.The results showed that the oscillation frequency of caudal fin,dorsal fin and anal fin increased with the increase of swimming speed.The swinging frequency of the dorsal fin and anal fin was higher than that of the caudal fin,and there was no significant difference between the adjacent dorsal fin and anal fin in 0.24m/s～0.48m/s groups.The trend rate of the flow rate group was significantly higher than that of the still water group,and there was no significant difference in the trend rate of the flow rate groups(P>0.05).(4)Six flow rate groups of 0.70m/s,0.65m/s,0.60m/s,0.55m/s,0.50m/s and 0.45m/s were set.The larvae of 10g size swam nearly 0mim,0mim,0mim,0.15±0.05min,10.4±3.2min,93.7±7.0min,respectively.The 15g specification swam nearly 0mim,0mim,0mim,0.38±0.10min,25.5±13.5min,140.0±35.6min respectively.When the flow rate was higher than 0.60m/s,juvenile fish at 10g and 15g sizes began to be washed away because they could not top the current.The juvenile fish with the size of 20g could not swim 0.70m/s after nearly 0mim,0.08±0.03min,0.32±0.05min,50±16.1min,126.7±15.6min and 324±27.6min,respectively.The larvae of 25g size swam nearly 0.3±0.1min,40±10.4 min,150±17.3min,326.6±75.4min,471±54.9min and 556±44.6min,respectively.The larger the size of the fish,the longer the swim time.With the same specification,the smaller the flow rate,the longer the swimming time.juvenile fish can swim only for a short time when their swimming speed is close to burst swimming speed.Juveniles can continue to swim for a period of time when the swimming speed is close to the critical swimming speed.In general,the swimming ability of Thamnaconus septentrionalis is strong,and there is a great difference between individual fish.2.Fish of 25g were downstream for 10min,30min and 60min at the four flow rates of standing water group(0.009m/s),0.12m/s,0.24m/s,0.36m/s and 0.48m/s at16℃.Lactic acid and glycogen in muscle,liver,blood and blood glucose were measured after exercise.The results showed that lactic acid content in muscle,blood and liver increased with the increase of flow rate and time,while blood glucose and glycogen decreased.The lactic acid content in muscle of 0.36m/s(10min)group began to increase and was significantly different from that of control group(P<0.05),and reached the maximum value in the highest group of 0.48m/s(60min).The lactate content of caudate muscle was higher in 0.36m/s(30min),0.36m/s(60min)and 0.24m/s(60min)groups,followed by gluteus muscle and back muscle.The gluteal muscle produced more lactic acid in 0.48m/s(30min)and 0.48m/s(60min)groups,followed by caudate muscle and back muscle,and the difference was significant compared with the control group(P<0.05).The lactic acid content in blood and liver showed an overall upward trend,and it increased significantly from 0.36m/s(P<0.05).The lactic acid content in muscle,blood and liver was the highest in 0.48m/s(60min)group.The glycogen content in muscle and liver decreased with the increase of flow rate and time,and the glycogen content in the highest 0.48m/s(60min)group was the lowest.From0.36m/s30min,the glycogen content was significantly different from that in the control group.From 0.24m/s group,the glycogen content in muscle began to decrease significantly.Blood glucose also showed a decreasing trend,and the lowest value was obtained in 0.48m/s(60min)group.The results showed that the juvenile Thamnaconus septentrionalis could increase the energy consumption and produce lactic acid in anaerobic metabolism at a flow rate higher than 0.36m/s for a long time.3.In order to understand the changes of oxygen consumption and activity of juvenile Thamnaconus septentrionalis with the decrease of dissolved oxygen in water at different temperatures,a closed breathing chamber was used in this study.The average body length of juvenile Thamnaconus septentrionalis was(9.5±0.08)cm at four temperature gradients of 12℃,16℃,20℃and 24℃.Oxygen consumption rate and asphyxiation point of juvenile Thamnaconus septentrionalis with body weight of(15.34±0.15)g were measured and analyzed.The results showed that the asphyxiation point was(0.85±0.064)mg/L at 12℃,(0.97±0.04)mg/L at 16℃,(1.10±0.05)mg/L at20℃and(1.40±0.07)mg/L at 24℃.The asphyxiation point increased with the increase of temperature.When the dissolved oxygen content was close to 2.14 mg/L,2.37 mg/L,2.40 mg/L and 3.06 mg/L,the young fish began to show uncomfortable behavior,and the young fish began to die to all death.The dissolved oxygen content decreased by 0.3 mg/L in each temperature group.The higher the temperature,the shorter the total death time.The oxygen consumption rate increased with the increase of temperature,and decreased from 0.104,0.131,0.187 and 0.318 mg/(g·h)at the beginning to 0.02 mg/(g·h)～0.03 mg/(g·h)at the end with the decrease of dissolved oxygen content.The higher the temperature,the faster the decrease.The change of oxygen consumption rate during the decrease of dissolved oxygen content in each temperature group was divided into suitable stage(Ⅰ),asphyxia stage(Ⅱ)and death stage(Ⅲ).The results showed that there were obvious changes in the three stages,and the oxygen consumption rate in each group showed a decreasing trend with significant differences among the three stages(P<0.05).The oxygen consumption rate of each temperature group in stageⅠandⅡincreased with the increase of temperature,and the difference was significant among all groups(P<0.05),while the difference was not significant among adjacent temperature groups in stageⅢ(P>0.05),and the difference was significant among non-adjacent groups.Therefore,the oxygen consumption rate of juvenile Thamnaconus septentrionalis has obvious changes with dissolved oxygen content and temperature.Generally speaking,the oxygen consumption is higher and the hypoxia tolerance is poor. |
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