Effects Of Restricted The Supply Of Dissolved Oxygen On The Growth Of Juvenile Brown Flounder, Paralichthys Olivaceus And The Mechanism

This thesis reviewed the research progress of hypoxia effect on the fish physiology and ecology. Methods of ecology, energetics, and physiology were used to investigate the effect of low dissolved oxygen (DO) content on growth, compensatory growth, energy allocation, energy metabolism, respiratory behavior, blood indexes and oxidative stress of juvenile brown flounder, Paralichthys olivaceus. The main results are as follows:1 Effect of restricted supply of dissolved oxygen on the growth, energy allocation, respiratory behavior and physiological signs of juvenile brown flounder, Paralichthys olivaceusThe effects of five different dissolved oxygen contents (DO 2.24±0.24, 3.14±0.24, 4.27±0.18, 5.38±0.25, and 6.94±0.14 mg/l) on the growth, energy allocation, respiratory behavior,blood indexes and oxidative stress of juvenile brown flounder, Paralichthys olivaceus are investigased in three experiments. The results showed that the fish grow fast in the water with DO above 5.38 mg/l and the model of energy allocation is be propitious to fast growth. The fish grow slowly when DO is lower than 2.4 mg/l and the energy allocated to growth is also decreased. Thus induced the follow physiological activity and lower oxygen consumption and these are disadvantageous for growth. DO has a significant effects on the energy ingestion and its allocation to respiration, feces, and growth. But the energy lose in excretion is not affected by DO significantly. In the experiment, restrictions on the supply of DO can intensify the respiratory rhythm,respiratory movement and mechanism of respiration in blood. That is less than optimal oxygen supply can lead to respiratory behavior and blood physiology appeared a series of changes and adaptation. Except for DO5.38, the hepatin of the muscle in other four treatments are not significantly different from each other. But it indicates that the hepatin of the muscle in the treatments with higher dissolved oxygen content are higher than that in the three treatments with lower DO content. When DO is lower than 4.27 mg/l, blood sugar of the fish rise and it indicates that when DO decrease to 4.27 mg/l will induce the fish to mobilize hepatin as energy resources. The lactic acid content of the muscle decrease in according to the decrease of DO when DO is below 3.14 mg/l. All of the anti-superoxide anion, SOD, GSH/GSSG, and malondialdehyde content are not significantly different among different treatments. But it is found that total anti-oxidative capacity of DO4.27 is significantly higher than control treatment. The parameters of oxidative stress indicate that the brown flounder could balance of oxidative and anti-oxidative system.2 Energy metabolism and oxidative stress of juvenile brown flounder, Paralichthys olivaceus during the decrease of dissolved oxygen content decreasingIn the experiment, the changes of oxygen consumption, ammonia nitrogen excretion, and oxygen to ammonia nitrogen excretion ratio (O:N) are detected during the decrease of DO from 7.4 mg/l to 0.9 mg/l. The oxygen consumption show"U"type dynamic in according to the decreasing of DO. This may be attributed to the increasing of oxygen consumption caused by increasing escaping and breathing behavior when oxygen decreasing. The dynamic of O:N is a type of inversion"U"and it indicates that the fish using hepatin as energy resource when DO decreasing. The results show that muscle MDA levels increase with the decrease of dissolved oxygen content. This shows that oxidative stress caused by hypoxia enhance the production of ROS which could increase lipid peroxidation, and juvenile brown flounder (Paralichthys olivaceus) still showed oxidative damage, although the muscle and liver SOD activity express an increasing trend.3 The compensatory growth of juvenile brown flounder, Paralichthys olivaceus following lower dissolved oxygen content stressIn this experiment the effects of dissolved oxygen (DO) on the compensatory growth is investigated. Juvenile P. olivaceus were exposed to water (DO 2, 4, and 7.5 mg/l) for 10 d and then switched to normoxic water (DO 7.5 mg/l). The results indicate that the weight of fish in S2 and S4 are significantly lower than that in S7.5 at the end of the first 10 d. But they catch up the control at the end of the first 10 d of recovery. The weight of fish in S2 and S4 do not exceed the control in the following periods. The daily growth coefficient indicate that the compensatory growth occur in the first 10 d of recovery. The compensatory growth following hypoxia is achieved mostly by improving feeding rate and at some extent by improving feed conversion efficiency. The fractions of respiration and excretion energy are higher during hypoxia and it contributes to lower feed conversion efficiency. On the contrary, less energy loss in respiration and excretion improve the feed conversion efficiency in recovery periods. The results indicate that the brown flounder can completely compensate the growth depression caused by short period of no-lethal hypoxia. Thus the short-term hypoxia in water will not impact the growth and fitness of juvenile brown flounder.