斑石鲷低氧耐受能力及血液生理生化指标变化研究

Hypoxia tolerance and alternation of blood physiological and biochemical indexes in spotted knifejaw Oplegnathus punctatus.

中文关键词: 斑石鲷  低氧耐受  呼吸频率  血液学  生理生化

英文关键词: Spotted knifejaw Oplegnathus punctatus  Hypoxia tolerance  Respiratory frequency  Hematology  Physiology and biochemistry

中文摘要:

      为阐明斑石鲷(Oplegnathus punctatus)低氧耐受能力及低氧胁迫过程中血液生理生化指标的变化规律，本研究通过生理学和生态学方法，查明2种规格斑石鲷在临界氧分压(critical oxygen tension, Pcrit)和失去平衡点(loss equilibrium, LOE)时的溶解氧浓度，观察自然耗氧条件下其呼吸行为变化，分析低氧胁迫和恢复溶解氧过程中血液皮质醇和葡萄糖含量、血红蛋白(hemoglobin, Hb)浓度、红细胞(red blood cell, RBC)和白细胞(white blood cell, WBC)数目、红细胞积压(hematocrit, HCT)变化。结果显示，在水温(23.0±0.5)℃、氨氮浓度<0.5 mg/L、亚硝酸盐浓度0~0.05 mg/L、盐度为30、pH为7.80的条件下，200和50 g斑石鲷的Pcrit值分别为(4.05±0.09)和(3.15±0.12) mg/L，LOE值分别为(1.16±0.08)和(0.93±0.11) mg/L，且50 g斑石鲷到达LOE值的时间(t=480 min)比200 g斑石鲷(t=110 min)更长；自然耗氧过程中，2种规格斑石鲷呼吸频率均呈先升高后降低的变化趋势，且均在Pcrit值处显著升高，达到最大值(P<0.05)。低氧胁迫导致血浆葡萄糖和皮质醇含量显著升高，在LOE值处达到最大值(P<0.05)，但50 g斑石鲷的葡萄糖和皮质醇含量上升幅度显著低于200 g斑石鲷(P<0.05)。同时，低氧引起斑石鲷的WBC和RBC数目、Hb浓度和HCT显著升高，50和200 g斑石鲷分别在Pcrit和LOE值处达到最大值(P<0.05)。恢复正常溶解氧24 h后，2种规格斑石鲷均恢复正常呼吸运动，上述生理生化指标均与对照组无显著差异(P>0.05)。综上所述，2种规格的斑石鲷相比较，50 g斑石鲷的低氧耐受能力更强，200 g斑石鲷对低氧胁迫的应激反应更敏感，2种规格斑石鲷均可通过增加呼吸频率、提高血液WBC和RBC数、皮质醇、葡萄糖和Hb浓度，增强对溶解氧的吸收利用，应对低氧胁迫导致的生理状态改变，相关结果为斑石鲷高效养殖提供了基础数据。

英文摘要:

      Dissolved oxygen is an important environmental factor affecting the growth and survival of aquatic organisms, including fish. Hypoxia has gradually become common in aquatic ecosystems and poses a significant challenge for fish farming. A decrease of dissolved oxygen levels in the body or a lack of oxygen will lead to a severe stress response for fish, hindering the development of the aquaculture economy. Dissolved oxygen is an important environmental factor that affects the aquaculture production of spotted knifejaw (Oplegnathus punctatus). The solubility of oxygen decreases with the increase of temperature, and the solubility of gaseous substances decreases with the increase of temperature and pressure. These show significant seasonal variation: The higher the temperature, the smaller the gap between the water molecules, and the lower the dissolved oxygen. Fish in a low-oxygen environment breathe normally and this can lead to physiological metabolic disorders, hence affecting fish behavior and physiological and biochemical indicators. However, in the process of evolution, fish have also developed different response modes and adaptive regulation mechanisms to maintain normal physiological functions. To clarify the changes in physiological and biochemical indices in blood during hypoxic tolerance and hypoxic stress, physiological and ecological methods were used in this study. The solubility of dissolved oxygen under two different specifications of critical oxygen tension (Pcrit) and loss equilibrium (LOE) were investigated, and the changes in respiration behavior under natural oxygen consumption were observed. Changes in cortisol and glucose, concentration of hemoglobin (Hb), number of red blood cells (RBC) and white blood cells (WBC), and hematocrit (HCT) during hypoxic stress and recovery were analyzed. Results showed that in a water temperature of (23.0±0.5)℃, the ammonia nitrogen concentration was less than 0.5 mg/L, nitrite concentration 0~0.05 mg/L, salinity 30 and pH 7.80; the dissolved oxygen concentrations at Pcrit were (4.05±0.09) mg/L and (3.15±0.12) mg/L for 200 g and 50 g O. punctatus, respectively. The concentrations of dissolved oxygen at LOE value were (1.16±0.08) mg/L and (0.93±0.11) mg/L. The time until the 50 g O. punctatus reached LOE (t=480 min) was longer than that of the 200 g O. punctatus (t=110 min). In addition, there were significant changes in respiration rate between hypoxia and re-oxygenation in both the 200 g and 50 g O. punctatus. In the process of natural oxygen consumption, the respiration rate of the two first increased and then decreased, and increased significantly at the Pcrit value. When the dissolved oxygen concentration decreased to 1.27 mg/L (420 min) and 1.10 mg/L (90 min), respiration rates of the 50 g and the 200 g fish reached their maximum (P<0.05). After recovery in normal dissolved oxygen for 24 h, the respiration rate did not differ significantly between the two sizes of O. punctatus nor with the control group. Plasma glucose and cortisol showed similar results to the respiratory rates; hypoxic stress led to significant increases and the highest values were obtained at LOE (P<0.05). The plasma cortisol concentration was the same in the two sizes of fish. While the values for the 50 g O. punctatus were significantly lower than those of the 200 g fish during hypoxic stress and re-oxygenation (P<0.05), the glucose and cortisol did not differ significantly from the control after recovery in normal dissolved oxygen for 24 h. Hypoxic stress had a significant effect on the blood biochemical indexes of O. punctatus. At Pcrit and LOE values, the number of WBCs, RBCs, Hbs and HCT, at 50 g were significantly higher than those in the control group (P<0.05), and the maximum values were at the Pcrit value. The concentrations of the four indexes were significantly increased in the 200 g O. punctatus compared with the control group (P<0.05). The maximum values of WBC, HCT, and Hb were reached at LOE, and the maximum values of RBC were reached at Pcrit. After recovery in normal dissolved oxygen for 24 h, the two sizes of O. punctatus showed normal swimming behavior and respiratory activities, and the above physiological and biochemical indexes did not differ significantly from those of the control group (P<0.05). Lastly, the body weight of O. punctatus differed during hypoxia-induced hematological and biochemical responses. In O. punctatus, the 50 g fish were more tolerant to hypoxic environments than the 200 g, while the 200 g fish were more sensitive to hypoxic stress. Both sizes of O. punctatus could enhance the absorption and utilization of dissolved oxygen by increasing their respiratory rate, increasing the number of WBCs and RBCs, and increasing the concentrations of cortisol, glucose, and Hb in response to hypoxia stress. In this study, the tolerance to hypoxia and the physiological responses of different sizes of O. punctatus were elucidated; their adaptability to low dissolved oxygen was explored, and their tolerance threshold to hypoxia was determined. The results provide data for land-sea relay breeding of O. punctatus, a theoretical basis for efficient land-sea relay, and an early warning range of hypoxia for breeding O. punctatus, to help reduce economic losses caused by decreased oxygen.