Effects Of Low Dissolved Oxygen On The Growth Of Chinese Shrimp, Fenneropenaeus Chinensis And The Mechanism

The domestic and foreign research advances regarding the effects of hypoxia on physiological ecology in crustacean were reviewed in this thesis. Menthods of ecology, energetics, and physiology were used to investigate the effects of low dissolved oxygen (DO) content on the growth, compensatory growth, energy allocation, oxygen consumption, metabolism, behavior, and oxidative stress of Chinese shrimp, Fenneropenaeus chinensis. The main results are as follows:1 Tolerance and response of behavior and metabolism to low dissolved oxygen of Chinese shrimp, Fenneropenaeus chinensisThe tolerance of low DO content and the responses of behavior and metabolism to hypoxia are important strategies for aquatic organisms to adapt to variable DO in water environment. In this chapter, four experiments were designed to investigate the tolerance of low DO and the responses of behavior and metabolism to hypoxia of Chinese shrimp, F. chinensis. The results of experiment I showed that the lethal dissolved oxygen (LDO) content of small shrimp (2.29±0.06 g) and large shrimp (12.21±0.09 g) were positively related to temperature above 20℃. The regression analysis showed that the temperature at minimum LDO (0.59 mg/l) was 14.7℃for small shrimp. In experimentⅡ, the small (9.03±1.32 g) and the large (19.21±1.86 g) shrimp could detect hypoxic water area and absolutely avoided the water area with DO below 2.0 mg/l. The shrimp seldom entered the water area with DO 2.0～2.5 mg/l. In experimentⅢ, the oxygen consumption and ammonia excretion of the shrimp (15.69±0.91 g) exposed to different DO for eight hours was measured. The oxygen consumption and ammonia excretion were positively related to DO below 4 mg/l. However, O:N was negatively related to DO. In experimentⅣ, an energy budget method was adopted to calculate the daily energy metabolic rate (R, J/g/d), daily energy lost rate of nitrogen excretion (U, J/g/d), and O:N. R and U diminished as DO decreasing and no significant effects of DO on O:N. Being exposed to hypoxic water for 30 days induced an increase of moisture content of the shrimp and decrease of protein, lipid, energy, and energy of glucide. The above results indicated that F. chinensis was sensitive to low DO content and it should be a limited oxygen-regulator. The critical dissolved oxygen (COL) content was about 4.0 mg/1 and when DO was below COL for a short period, F. chinensis could adjust the composition of metabolic substrate to achieve a higher oxycalorific coefficient. But for a long term low DO, the metabolic substrate was from feed and its composition would not be changed by DO decrease.2 Effects of limited dissolved oxygen supply on the growth and energy allocation of juvenile Chinese shrimp, Fenneropenaeus chinensisInformation about the effect of hypoxia exposure on energy allocation is helpful for better understanding how aquatic animals tolerate and adapt to the hypoxic environment. The growth, molting, and energy allocation were investigated in juvenile F. chinensis exposed to five different dissolved oxygen seawaters (DO 2.09±0.15,3.10±0.29,4.13±0.25,4.73±0.12, and 5.48±0.09 mg/1) for 30 days. When DO was below 4.13 mg/l, the growth of shrimp was depressed. Feeding rate and feed conversion efficiency decreased with DO decrease. Less feed ingestion was caused by lower daily metabolic energy. Higher proportion of ingested energy lost in metabolism, exuviations, and nitrogen excretion caused lower feed conversion efficiency. More energy lost in exuviations, lower survival rate, soft carapaces of dead shrimp, and cannibalism were found in oxygen deficient groups and it implicated that hypoxia could delay the shrimp recovering from molting and cause cannibalism and higher mortality. The results indicated that hypoxia was an important factor affecting the amount and fitness of shrimp stock because it could cause a high rate of mortality and growth depression.3 Compensatory growth of Chinese shrimp, Fenneropenaeus chinensis following hypoxic exposureCompensatory growth following stress is a strategy which aquatic animals use to adjust themselves to a variable environment. Studies on the recovery growth of aquatic animals are not only of theoretical value in ecophysiology and evolution, but also important to applications in aquaculture and fisheries resource management. In this experiment, juvenile F. chinensis with an initial average body weight of about 3.72 g were exposed to hypoxic water (DO about 2.08 and 3.11 mg/1) for 10 days and then switched to normoxic water (DO about 5.63 and 5.59 mg/1). Compared to the juveniles in normoxia, juveniles in the hypoxia period allocated a greater proportion of energy to metabolism and exuviations, but allocated less energy to daily metabolism per gram shrimp weight (J/g/d). This reduced feed conversion efficiency and feeding rate. Finally, F. chinensis suffered growth depression. The juveniles completely compensated for hypoxia-induced growth depression in 30 days after being switched into normoxic water and the compensation was achieved mainly by hyperphagia and slightly by improvement of feed conversion efficiency. During the recovery period, the hypoxic-stressed shrimp showed higher daily metabolic energy (J/g/d) than controls (P<0.05). This means the stressed shrimp had more energy for feeding-related activities. So hyperphagia was observed. Energy analysis indicated that F. chinensis improved feed-conversion efficiency mainly by reducing the percentage of energy lost in feces and exuviations. The results showed that short-term non-lethal hypoxia would not affect the growth of juvenile F. chinensis if there were enough time for the stressed shrimp to recover. It suggested F. chinensis was able to adapt to DO fluctuation to some extent and short-term non-lethal hypoxia would not have an obvious effect on natural, released, and cultured shrimp stock.4 Hypoxia and recovery perturb oxidative stress of Chinese shrimp, Fenneropenaeus chinensisThe effects of hypoxia exposure 3-24 h and following normoxic recovery 3-24 h on the levels of lactic acid, lipid peroxidation (malondialdehyde), activities of anti-superoxide radical and the total antioxidant capacity status were measured in muscle, gill, hepatopancreas, and plasma of the Chinese shrimp, F. chinensis. Results indicated differences among tissues, even under control conditions. Under hypoxia 12 h and 6 h, lactic acid levels in muscle and plasma were increased significantly, but decreased to the same levels as control in hypoxia 24 h. Followed by 12 h of normoxic recovery, lactic acid levels in muscle increased significantly. Hypoxia exposure did not show a significant effect on the lactic acid levels in hepatopancreas and gills, total antioxidant capacity status in muscle, gills and hepatopancreas, activities of anti-superoxide radical in hepatopancreas and gills, malondialdehyde levels in muscle, hepatopancreas, gills and plasma. But during reoxygenation, the total antioxidant capacity status in hepatopancreas, activities of anti-superoxide radical in gills, and levels of malondialdehyde in muscle, gills and plasma increased significantly at different time, which could cause tissue damage. The results showed that the oxidative stress during normoxic recovery was greater than during hypoxia exposure. After 24 h of normoxic recovery, most parameters were at the same levels as control, but the lactic acid levels in muscle, activities of anti-superoxide radical in gills, malondialdehyde levels in gills and plasma were still higher than control groups. Under the condition of 26.0±1.0℃, salinity 30～31, pH 7.9±0.2, Chinese shrimp showed a certain degree of ability to to tolerate and adapte to acute hypoxia (DO 2.0±0.1 mg/l) and following reoxygenation.