Effects Of Dissolved Oxygen On The Growth, Metabolism And Oxidative Stress Of Pelteobagrus Fulvidraco Richardson

The present study was conducted to investigate the effects of dissolved oxygen on the growth, metabolism and oxidative stress of yellow catfish with the method of experimental ecology and physiology under indoor controlled condition. This study consists of three parts, the first part investigated instantaneous oxygen consumption rate and suffocation point of yellow catfish; the second part investigated effects of dissolved oxygen on feed intake, growth and respiratory metabolism of juvenile yellow catfish; the third part investigated effects of dissolved oxygen on the growth, energy budget and oxidative stress of yellow catfish. Its main findings as fellows:In this experiment, instantaneous oxygen consumption rate (IRO2) and suffocation point (Sp) of yellow catfish (BL:1.90～11.03 cm, BW:0.17～22.99 g) were investigated by means of sealed-still water at 28±0.5℃. The results showed that the range of Sp and IRO2 was 0.33～0.60 mg/L and 0.0119～0.2081 mg/g·h. Both Sp and IRO2 of yellow catfish decreased with size increasing, and the power function between Sp and size, and IRO2 and size can be described as Sp=0.7795L-0.3695(R2= 0.9619), Sp=0.4897W-0.1323 (R2=0.9656) and IRO2=0.7284L-0.5709 (R2=0.9580), IRO2= 0.3549W -0.2036(R2= 0.9539), respectively. IRO2 of yellow catfish decreased with decreasing dissolved oxygen (DO) and there were linear correlations between IRO2 and DO. This study suggests that yellow catfish has low suffocation point and its breath relegates to compliant style.A 6-week feeding experiment was conducted to investigate the effects of dissolved oxygen (DO) levels on feed intake, growth and respiratory metabolism of juvenile yellow catfish (initial weight:1.62±0.02 g per fish) reared in 300-L indoor flow-through circular fiberglass tanks in 28±0.5℃. Four DO levels were hypoxia (G1,2.92 mg/L), moderate hypoxia (G2,4.71 mg/L), saturation (G3,6.77 mg/L) and super-saturation (G4,9.68 mg/L), respectively. The results showed that specific growth rate and feed conversion efficiency were significantly higher in the normoxic group (G3) than in the other groups (P< 0.05). The oxygen consumption and ammonia excretion rate of experimental fish had no direct correlation with dissolved oxygen, which was significantly higher in the saturation than in the hypoxia and super-saturation. The experiment showed that after the tested fish ate its food in 4 hours the both rates increased drastically at 09:00 and 21:00, and reached their maximum levels, then decreased slowly towards to their nomal levels. The highest oxygen consumption rate were 0.345 mg/g·h and 0.331 mg/g·h and ammonia excretion rate were 24.194μg/g·h and 17.770μg/g·h in the saturated group (G3). This study suggests that response in the rate of ammonia excretion in juvenile yellow catfish should be relative closely to response in the oxygen consumption and saturation was considered to be highest for growth and respiratory metabolism.A 8-weeks feeding experiment was conducted to investigate the effects of dissolved oxygen levels (DO) on growth performance, feed utilization, nitrogen metabolism and oxidative stress of yellow catfish. Four dissolved oxygen levels were formulated. Experimental fish were reared at oxygen levels of hypoxia (D1,2.28 mg/L), moderate hypoxia (D2,4.04 mg/L), saturation (D3,6.51 mg/L) and super-saturation (D4,9.11 mg/L). During the experiment, the experimental fish was reared in re-circulating system and water temperature was 28℃. The results showed that the specific growth rate in wet weight (SGRw) and feeding rate (FR) increased significantly, when DO be above 6.51 mg/L. Feed conversion efficiency of dry weight (FCEd) and energy (FCEe), apparent digestibility coefficient of dry matter (ADCd) and gross energy (ADCe) increased with the increasing with DO increment within the range of 2.28～9.11mg/L, but no significant difference was found among D3 and D4 groups (P>0.05). The highest gross energy intake (C) and growth energy (G) were 434.39 J/g·d and 77.89 J/g·d in the D3 group, then decreased slowly in D4 group. The general direction in the value of energy of respiratory metabolism (R) was similar closely to C and G. The contents of malondialdehyde (MDA) in liver and serum were the lowest in the D3 group. Activities of superoxide dismutase (SOD) and catalase (CAT) were the highest and activities of glutathione peroxidase (GSH-PX) were no significantly affected in the liver of yellow catfish exposed to 6.51 mg/L DO. Activities of SOD,GSH-PX,CAT in the serum were the highest in the D3 group. The results indicated that metabolism of growth and nitrogen and activities of the antioxidant defense were promoted in yellow catfish exposed to saturated DO level.