Studies on salinity-dependent responses to low-temperature induced oxidative stress in livers of the euryhaline milkfish(Chanos chanos)

• Main Authors: Chia-Hao Chang, 張家豪
• Other Authors: Tsung-Han Lee
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/y7vj2g

博士 === 國立中興大學 === 生命科學系所 === 106 === Milkfish (Chanos chanos) is an important economic aquaculture species in Southeast Asia and Taiwan. The euryhaline milkfish is a marine species that can be reared in ponds with fresh water (FW) or seawater (SW). In addition, milkfish was intolerant to water temperature below 12°C during cold snap in winter. Temperature fluctuation is an important factor to affect physiological responses in ectothermic species, including fish. The SW-acclimated milkfish was reported to have better cold tolerance than the FW-acclimated milkfish. To illustrate the mechanisms for different hypothermal tolerance between FW- and SW-acclimated milkfish, this dissertation was divided into four chapters to further explore the salinity-dependent responses of euryhaline milkfish livers to low-temperature induced oxidative stress. In the first chapter, SW milkfish treated with nonlethal low-temperature (18°C) and lethal low-temperature (16°C) were used to identify unique proteins related to various stress responses by proteomics analyses. Two major physiological responses including the antioxidative and apoptotic pathways were categorized in livers of SW milkfish. Therefore, in the second chapter, the antioxidative enzyme, peroxiredoxin 6 (Prdx6), detected in the proteomics analysis of the first chapter, were up-regulated in both transcript and protein abundance of FW milkfish after transfer to 18°C for 24 h and 6 h, respectively. The H2O2 contents in livers of FW milkfish were elevated under hypothermal stress. Although the hepatic protein abundance of Prdx6 was down-regulated in SW milkfish, enhanced ratio of protein abundance of Prdx6 in membrane fraction has maintained the redox status and structure of plasma membrane. The H2O2 induced Ccprdx6 transcript by the ex vivo experiment indicating the ability of Prdx6 to be an antioxidant. Moreover, the antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase) and the apoptotic protein activity (caspase-3) were identified in the third chapter. Although the antioxidant mechanisms of FW milkfish was up-regulated under hypothermal stress, the hepatocytes were shrinked and apoptosis occurred via extrinsic pathway. The SW milkfish under the same hypothermal stress, however, did not exhibit apoptosis of hepatocytes. In the last chapter, the expression of isoform 1 of superoxide dismutase (Sod1) in FW and SW milkfish were up-regulated after exposure to hypothermal stress for 3 h and 96 h, respectively. The results supported extrinsic apoptotic responses and suggested pathogen infection status under hypothermal stress. Taken together, molecular and physiological ways were used for analyses and revealed that hepatic redox status were affected more in FW milkfish, leading to cellular apoptosis via extrinsic apoptotic pathway. The results of this study provided new insights for salinity effects on milkfish livers in response to cold stress.