间歇式浊度暴露对文蛤幼贝生长和代谢的影响

Effects of Intermittent Turbidity Exposure on the Growth and Metabolism of Juvenile Meretrix meretrix

摘要:

机械化采捕作业过程引起海水浊度发生间歇性变化，可能对未达到商品规格再次回落到海底的幼贝产生重要影响，本研究以文蛤(Meretrix meretrix)幼贝为研究对象，采用每日(24 h)浊度暴露6 h+恢复18 h的间歇式暴露模式，模拟了短期浊度暴露(7 d)对鳃和肌肉组织酶活性的影响，以及长期暴露(60 d)对生长、存活和鳃组织的影响，实验共进行60 d。实验设置2(对照组)、10、50和100 NTU四个海水浊度处理，在实验开始后的第1、3、7 d分别采集暴露期和恢复期贝类样品，测定鳃组织超氧化物歧化酶(SOD)、酸性磷酸酶(ACP)和闭壳肌丙酮酸激酶(PK)、磷酸果糖激酶(PFK)活性；实验结束时(60 d)测定幼贝生长率和存活率，并观察其鳃组织的结构变化。结果表明：(1)鳃SOD和ACP活性随浊度升高显著下降(P<0.05)，暴露7 d，暴露6 h期间100 NTU组SOD和ACP活性分别为对照组的37.7%和32.6%，恢复期间，100 NTU组SOD和ACP活性仅回升至对照组的43.2%和49.1%，另外，恢复程度显著也显著低于10NTU组和50NTU组(P<0.05)，表明高浊度条件下文蛤幼贝的抗氧化与免疫功能修复能力受限。(2)闭壳肌PK和PFK活性呈先升高后降低趋势，暴露3 d时，100 NTU组PK和PFK活性显著高于对照组(P<0.05)，分别为对照组的122.4%和232.1%，而暴露7 d时，PK活性降至对照组的53.0%(P<0.05)，而PFK活性仍显著高于对照组(P<0.05)，但较暴露3d显著降低；暴露7d恢复期间，100NTU组PK和PFK活性未见恢复。(3)60 d暴露结束时，100 NTU组幼贝存活率为(55.6±4.8)%、壳长和湿重特定生长率分别为(0.15±0.04)%/d和(0.21±0.05)%/d，均显著低于对照组(P<0.05)，50 NTU组生长指标亦显著受抑。(4)组织切片结果显示，鳃丝间距随浊度升高显著增大(P<0.05)，100 NTU组出现上皮细胞空泡化、鳃小片缩窄等不可逆损伤。研究表明，50 NTU以上浊度暴露可导致文蛤幼贝抗氧化、免疫与能量代谢系统持续受损，且恢复能力随浊度升高而减弱。

Abstract:

Mechanized harvesting can cause intermittent increases in seawater turbidity, which may have important effects on undersized juvenile Meretrix meretrix that resettle on the seabed after disturbance. In this study, Meretrix meretrix juveniles were used as the experimental animals to investigate the effects of short-term turbidity exposure on enzyme activities in gill and muscle tissues, as well as the effects of long-term turbidity stress on survival, growth, and gill histological structure. Four turbidity levels were set, namely 2 NTU as the control and 10, 50, and 100 NTU as the experimental groups. An intermittent exposure regime was applied, consisting of 6 h of turbidity stress and 18 h of recovery each day. On days 1, 3, and 7 after the beginning of the experiment, samples of Meretrix meretrix were collected during both the stress period and recovery period. The activities of superoxide dismutase (SOD) and acid phosphatase (ACP) in gill tissue, together with pyruvate kinase (PK) and phosphofructokinase (PFK) in the adductor muscle, were determined. At the end of the 60-day experiment, survival, growth performance, and gill histological changes were further examined. The results showed that SOD and ACP activities decreased significantly with increasing turbidity (P < 0.05). At the end of the 7-day stress period, SOD and ACP activities in the 100 NTU group were only 37.7% and 32.6% of those in the control group, respectively. After 7 days of recovery, the two enzyme activities in the 100 NTU group recovered only to 43.2% and 49.1% of the control levels, and the recovery degree was significantly lower than that in the 10 NTU and 50 NTU groups (P < 0.05). These results indicated that high turbidity restricted the recovery of antioxidant and immune functions in juvenile Meretrix meretrix. PK and PFK activities showed a trend of first increasing and then decreasing. On day 3 of the stress period, PK and PFK activities in the 100 NTU group were significantly higher than those in the control group (P<0.05), reaching 122.4% and 232.1% of the control levels, respectively. At the end of the 7-day stress period, PK activity in the 100 NTU group decreased significantly to 53.0% of the control group (P<0.05), whereas PFK activity remained significantly higher than that in the control group, although it was significantly lower than that on day 3. After 7 days of recovery, PK activity in the 100 NTU group did not recover, while PFK activity increased to some extent but was still lower than that in the control group. This suggested that the recovery of energy metabolism in juvenile Meretrix meretrix was incomplete and unbalanced under high turbidity stress. At the end of the 60-day exposure, the survival rate, shell length specific growth rate, and wet weight specific growth rate in the 100 NTU group were significantly lower than those in the control group (P<0.05), with values of (55.6±4.8)%, (0.15±0.04)%/d, and (0.21±0.05)%/d, respectively. Growth in the 50 NTU group was also significantly inhibited. Histological observations showed that the spacing between gill filaments increased significantly with increasing turbidity (P<0.05). In the 100 NTU group, epithelial cell vacuolation and narrowing of gill lamellae were observed, indicating irreversible tissue damage. In conclusion, turbidity stress above 50 NTU caused persistent impairment of antioxidant, immune, and energy metabolic functions in juvenile Meretrix meretrix, and the recovery capacity weakened with increasing turbidity. These findings provide a scientific basis for evaluating the biological effects of intermittent turbidity disturbances caused by mechanized harvesting on juvenile Meretrix meretrix.