镉对绿鳍马面鲀幼鱼急性毒性、肝脏抗氧化能力及组织结构的影响

Acute effects of cadmium on the antioxidant enzyme activities and histological structure of the gills and liver of juvenile Thamnaconus septentrionalis

中文关键词: 绿鳍马面鲀  镉  组织结构  抗氧化酶

英文关键词: Thamnaconus septentrionalis  Cadmium  Tissue structure  Antioxidant enzyme

中文摘要:

      本研究采用静水生物测试法测定了镉(Cd2+)对绿鳍马面鲀(Thamnaconus septentrionalis)幼鱼的急性毒性。根据预实验结果，设定8.19、9.18、10.30、11.56 mg/L共4个Cd2+浓度梯度进行急性毒性实验，根据急性毒性实验结果，设定1.84、2.76、3.68和4.60 mg/L 4个不同浓度Cd2+急性暴露实验，分别在6、12、24、48、72和96 h检测肝脏中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、谷胱甘肽抗氧化酶(GSH-PX)活性及丙二醛(MDA)含量，观察肝脏、鳃组织结构的变化。结果显示，随着Cd2+浓度的增加，急性毒性效应逐渐增强，24、48、72和96 h半致死浓度 (LC50)分别为11.47、10.82、9.84和9.19 mg/L，Cd2+对绿鳍马面鲀幼鱼的96 h安全浓度为0.92 mg/L。6 h时，各浓度组SOD和CAT活性与对照组相比显著升高；6—48 h时，SOD、CAT、GSH-PX活性均呈先上升后下降的趋势；48—96 h时，各浓度组酶活性均呈下降趋势，且时间越长，浓度越大，活性越低。与对照组相比，MDA含量整体呈先降低后增加的趋势，12—48 h时，1.84和2.76 mg/L组MDA含量有波动，3.68、4.60 mg/L组MDA含量与时间和浓度成正比。24 h时，1.84 mg/L组肝脏组织未见明显变化，2.76、3.68和4.60 mg/L组肝脏组织开始受到明显损伤，表现为细胞体积增大且形状不规则，细胞膜边界模糊，1.84和2.76 mg/L组鳃组织相比无显著变化，3.68和4.60 mg/L组出现鳃小片弯曲，上皮细胞水肿膨大，相邻鳃小片相互黏连融合，无游离端，细胞坏死脱落等损伤现象。在安全浓度为0.92 mg/L内绿鳍马面鲀幼鱼可健康生长，SOD、CAT和GSH-PX活性变化及MDA含量反映了绿鳍马面鲀幼鱼受损害程度，可作为安全性风险评价的参考依据。

英文摘要:

      The acute toxicity of cadmium (Cd2+) to juvenile Thamnaconus septentrionalis was determined using a hydrostatic biological assay. According to the pre-experiment results, four Cd2+ concentration gradient test groups (8.19, 9.18, 10.30, and 11.56 mg/L) and one blank control group were selected for the acute toxicity test using the equilogarithmic spacing method. The mortality, LC50, and safe concentration of Cd2+ in juvenile fish at 24 h, 48 h, 72 h, and 96 h were calculated. Based on the experimental results of acute toxicity of Cd2+ to juvenile Thamnaconus septentrionalis, the Cd2+ concentration gradients were set as 1.84 mg/L, 2.76 mg/L, 3.68 mg/L and 4.60 mg/L at the safe concentration multiple. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione antioxidant enzyme (GSH-PX), and the content of malondialdehyde (MDA) in liver and gill tissues were observed at 6 h, 12 h, 24 h, 48 h, 72 h and 96 h. The results showed that as Cd2+ concentration increased, the acute toxicity gradually increased, the LC50 at 24 h, 48 h, 72 h and 96 h was 11.47 mg/L, 10.82 mg/L, 9.84 mg/L, and 9.19 mg/L, respectively, and the safe concentration of Cd2+ on juvenile filefish was 0.92 mg/L at 96 h. Within 6 h, SOD activity in each concentration group was significantly higher than that in the control group (P<0.01); SOD activity first decreased and then increased within 6–24 h; however, from 24 h to 96 h, SOD activity of all concentration groups showed a downward trend. SOD activity in the 1.84 mg/L and 2.76 mg/L groups was always higher than that in the control group within 96 h. The enzyme activities of the 3.68 mg/L and 4.60 mg/L groups decreased to below that of the control group from 6 h to 12 h, and increased at 24 h, after which it showed a constant downward trend and remained lower than that of the control group. From 6–12 h, MDA content first decreased and then increased. At 24 h, the enzyme content in each treatment group decreased, but was still higher than that in the control group, and the difference was significant (P<0.05). From 12 h to 48 h, the 1.84 mg/L and 2.76 mg/L groups showed a trend of first decreasing and then increasing, whereas within the 24 h to 96 h period, the MDA content in the 3.68 mg/L and 4.60 mg/L groups kept increasing, and was significantly higher than in the control group (P<0.01). At 6 h, CAT activity in all treatment groups was significantly increased when compared to that of the control group; however, CAT activity in the 3.68 mg/L and 4.60 mg/L groups was significantly inhibited at 48–96 h. Overall, the activity of GSH-PX in each treatment group showed a decreasing, increasing, and then decreasing trend within 6–96 h. The activity of GSH-PX in the 1.84 mg/L group was higher than that in the control group within 96 h. When compared with the control group, the activity of the 2.76 mg/L and 3.68 mg/L groups decreased from 24 h to 96 h, and the longer the stress time, the lower the activity. In the highest concentration group (4.60 mg/L), the enzyme activity first increased and then decreased, and the GSH-PX activity decreased to 300.12 U/mg prot at 96 h, which was significantly different from that in the control group (P<0.01). In the 1.84 mg/L group, there was no significant change in liver tissue within 72 h, but in the 1.84 mg/L group at 96 h and the 2.76 mg/L group at 24 h, the cell volume was slightly increased, cells had an irregular shape, and some cell membrane boundaries were blurred. At 48–96 h in the 2.76 mg/L group, and 24–48 h in the 3.68 mg/L and 4.60 mg/L groups, the liver cells were disordered and scattered, and the structure of liver cells was mostly incomplete. After 72–96 h in the 3.68 mg/L group and 72 h in the 4.60 mg/L group, the abnormality of liver cells was significantly aggravated, including cell hypertrophy, large area disintegration, cytoplasm overflow, and cell cavitation. At 96 h in the 4.60 mg/L group, the nucleus shrank, intracellular material gathered, and a large irregular blank appeared. For 72 h in the 1.84 mg/L group and 24 h in the 2.76 mg/L group, there was no significant change in gill tissue structure, whereas after 96 h in the 1.84 mg/L group, 48 h in the 2.76 mg/L group, and 24 h in the 4.60 mg/L group, the gill microplates were curved and club-like with mucus secreted around them, and the epithelial cells were enlarged, showed edema and partial hyperplasia, and the distance between the adjacent lamella became smaller. At 72 h in the 2.76 mg/L group, and at 24–48 h in the 3.68 mg/L and 4.60 mg/L groups, a small number of adjacent gill lamellae would fuse and form a small epithelial cell plate, with a large amount of mucus around them, and the length of gill lamellae was significantly shortened. In the 2.76 mg/L group at 96 h and the 3.68 mg/L group at 72 h, most of the basal lamellae had fused together, the epithelial cells of the gill lamellae were swollen and showed hyperplasia, and exfoliated epithelial cells were scattered around. At 96 h in the 3.68 mg/L group and 72–96 h in the 4.60 mg/L group, adjacent gill lamellae had adhered and fused with each other without a free end, and a large number of cells were necrotic and exfoliated.