Dynamic Changes Of Key Enzymes And Antioxidant Level In The Early Developmental Stages Of Carassius Auratus Under Mercury And Copper Exposures

Mercury and copper are trace metals which are commonly found in waters, and copper is also a necessary trace element in the metabolic processes of various organisms.The high concentration of heavy metals have harmful effects on organisms and the stability of the food chain and the aquatic biological community. Early development stage is the most important stage of life process of goldfish, which is vulnerable to the outside stress. In the responses to mercury and copper stress, physiological and biochemical indexes will change to attenuate the damages resulted from the stress. It is of important significance to recognize the changes of the key enzyme activity and MDA content under the exposures of mercury and copper. To study the changes of key enzymes and the status of oxidative stress in fish embryo and larvae subjected to mercury and copper stress is important to understand the impacts of mercury and copper on embryonic development and larvae development, as well as to assess the potential risk of mercury and copper pollution in aquaculture.In this study, the embryos and larvae of goldfish C. auratus were exposed to the different Hg²⁺ concentrations (0, 0.2, 1, 5 and 10μg L^-1 ) and Cu²⁺ concentration (0,0.1, 0.4, 0.7, 1.0 ppm) during the process of development, which were sampled to be used to analyze biochemical indices of acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), catalase (CAT) and lysozyme (LSZ) activities, as well as Malondialdehyde (MDA) content.The results showed that the activity changes of different enzymes appeared to be different. (1)Acid phosphatase and alkaline phosphatase activities were both low at 24 h after fertilization. With the process of embryonic development, alkaline phosphatase activities significantly increased and got to highest value at 144 h. Acid phosphatase also significantly rose after 96 h. Lysozyme and catalase activities both decreased with the development of embryos.The lysozyme activities of embryos at 96h decreased to the bottom and the value is (0.450±0.064) U·mg-1. Catalase activity at 120h also went down to a minimum value, which was significantly lower than that of embryos at 24h (p<0.05). For MDA content, it increased gradually in the process of embryonic development.(2)The enzyme activities of ACP, AKP and LSZ of the embryos were induced to increase under mercury exposure, while, CAT activity was inhibited obviously.Additionally, MDA content had remarkablely increased to respond to mercury exposure.(3)When the larvae were exposed to different Hg²⁺ concentrations (0, 0.2, 1, 5 and 10μg L^-1), ACP and AKP activities were induced under higher Hg²⁺ concentrations at Day 7 and 15 after exposure. LSZ and SOD activities were enhanced by 10μg L^-1 Hg²⁺ solution after 15d exposure.CAT activity was elevated in 10μg L^-1 Hg²⁺ solution after 7d and 15d exposure. MDA content increased in 10μg L^-1 Hg²⁺ solution after 7d exposure and it also increased in 5μg L^-1 and 10μg L^-1 Hg²⁺ solution after 15d exposure.(4)ACP activity of the embryos was induced to increase under copper exposure,especially when they were exposed in 1 ppm Cu²⁺ solution. The enzyme activities of AKP, LSZ and CAT of the embryos were inhibited obviously. Additionally, MDA content had remarkablely increased to respond to copper exposure.(5)The activites of ACP, AKP and LSZ of the larvae were induced to increase under copper exposure. The activities of SOD and CAT were induced to increase when the larvae were exposed to copper solution after 7d and 15d.Thus, MDA content also increased when the larvae were exposed to copper solution after 7d and 15d.In conclusion, (1)Acid phosphatase and Alkaline phosphatase activities are enhanced with the extension of embryonic development, which is due to the increasing demand of phosphatases enrolled in cell proliferation, signal transduction and physiological metabolism with the embryonic development.The reason of decreasing of lysozyme and catalase activities is that the maternal metabolism enzymes were consumed and reduced gradually with the development of embryos, and the ability to synthesize these enzymes in embryo is very weak. The decrease of catalse activity may result in the surplus of reactive oxygen species and subsequently lead to the gradual accumulation of MDA content.(2)The activities of key enzymes and the content of MDA were sensitive to mercury and copper exposure in the embryonic and larval development process of C. auratus. The changes in this study is mainly used to enhance its ability to cope with the stress of mercury and copper, and attenuate the damage resulted from the mercury and copper stress, and to maintain fish embryo and larvae in normal development. The biochemical indices in this study were demonstrated to be sensitive to mercury and copper exposure, which could be used as biomarkers to assess the potential ecological risks resulted from mercury and copper pollution to C. auratus embryonic and larval development.