Affiliation:
1. College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China
2. Key Laboratory of Efficient Utilization and Processing of Marine Fishery Resources of Hainan Province, Sanya Tropical Fisheries Research Institute, Sanya 572018, China
3. South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China
4. Hainan Engineering Research Center for Deep-Sea Aquaculture and Processing, Sanya 572018, China
5. International Joint Research Center for Conservation and Application of Fishery Resources in the South China Sea, Sanya 572018, China
6. College of Science and Engineering, Flinders University, Adelaide 5001, Australia
Abstract
This study investigated the effects of acute ammonia nitrogen (NH3-N) exposure on kidney antioxidant ability and phosphatases and related gene expression in juvenile yellowfin tuna (Thunnus albacares). The 180 juvenile yellowfin tuna (260.39 ± 55.99 g, 22.33 ± 2.28 cm) were exposed to ammonia for 6, 24, and 36 h using natural seawater (0 mg/L) as a control and NH3-N at 5 and 10 mg/L. The lipid peroxidation byproduct malondialdehyde (MDA) and the levels of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), alkaline phosphatase (AKP), and acid phosphatase (ACP), were measured using the colorimetric method in the trunk kidney to determine changes in antioxidant ability and phosphatase activity of juvenile yellowfin tuna exposed to NH3-N. Results indicated that, at 36 h, MDA, SOD, CAT, and GSH-PX levels rose in the 5 mg/L group versus the control. In the 10 mg/L group, MDA and SOD, CAT, and GSH-PX activities significantly increased after 24 and 36 h exposure compared to the control. Phosphatases play a pivotal role in the immune system. AKP activity significantly increased at 6 h, and ACP activity markedly rose at 36 h in the 5 mg/L group versus the control. Real-time fluorescence quantitative PCR was applied to detect alterations in the antioxidant genes SOD2, CAT, and glutathione peroxidase 1b (GPX1b) and immune cytokines-related genes Interleukin 10 (IL-10) and Interleukin 6 receptor (IL-6r) expression in the head kidney in juvenile tuna. Relative to the control, antioxidant gene expression in the 5 mg/L group significantly rose at 6 and 36 h, and in the 10 mg/L group, SOD2 and GPX1b were significantly elevated at 36 h. Compared to the control group, IL-10 expression in the 5 mg/L group significantly increased at 6 h, whereas IL-6r expression decreased. In the 10 mg/L group, both IL-10 and IL-6r levels were observed to be lower. Low ammonia nitrogen concentrations boost antioxidant defenses, phosphatase activities, and gene expression levels, whereas higher levels may induce suppressive effects. In yellowfin tuna juvenile farming, NH3-N concentration significantly affects the health of the juveniles. When the NH3-N concentration is between 5–10 mg/L, the stress duration should be limited to 24 h; if the concentration is below 5 mg/L, the stress duration can be extended to 36 h.
Funder
Hainan Major Science and Technology Project
Project of Sanya Yazhou Bay Science and Technology City
Central Public-Interest Scientific Institution Basal Research Fund, CAFS
Central Public-Interest Scientific Institution Basal Research Fund South China Sea Fisheries Research Institute, CAFS
Hainan Provincial Natural Science Foundation of China
Hainan Province Science and Technology Special Fund
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