Responses of acid/alkaline phosphatase, lysozyme, and catalase activities and lipid peroxidation to mercury exposure during the embryonic development of goldfish Carassius auratus

This study assessed the impact of mercury exposure on goldfish (Carassius auratus) embryos based on the dynamic characteristics of chemical parameters. Day-old embryos were exposed to different Hg²⁺ concentrations (0, 0.2, 1, 5, and 10μg/L). Subsequently, the embryos were sampled every 24h during embryonic development to measure acid phosphatase (ACP), alkaline phosphatase (AKP), lysozyme (LSZ), and catalase (CAT) activities, as well as malondialdehyde (MDA) content. The results revealed that the responses of ACP and AKP to mercury exposure presented in dose-dependent and time-dependent manners. The enzyme activities were significantly induced with increased concentrations and extended exposure (at 5μg/L after 72h and 10μg/L after 48h; p<0.05 or p<0.01). LSZ was not sensitive to lower Hg²⁺ concentrations, whereas LSZ significantly increased at higher concentrations and longer exposure (at 5μg/L at 120h and 10μg/L after 72h; p<0.05 or p<0.01). CAT activities were significantly inhibited at different periods of embryonic development, particularly at 5 and 10μg/L (p<0.05 or p<0.01). Reduced CAT activities were observed at 72, 96, and 120h at 1μg/L (p<0.05 or p<0.01), whereas a decline at 0.2μg/L was evident at 96h (p<0.01). MDA content significantly increased at various stages of embryonic development, particularly at 10μg/L (p<0.05 or p<0.01), and increased further at 72, 96, and 120h at 5μg/L (p<0.05 or p<0.01). At 96h, MDA content was only increased by exposure to 0.2 and 1μg/L (p<0.01). The activities of ACP, AKP, and LSZ remarkably increased at 120h in contrast to 96h (p<0.05 or p<0.01). Therefore, 96h is an important shifting period of embryonic development because the activity of enzyme has been enhanced at this time. Thus, the increased ACP, AKP, and LSZ activities revealed an enhanced ability of the embryo to synthesize more enzymes and attenuate mercury damage. CAT activity negatively correlates with MDA accumulation. The enhanced enzyme activities after specific embryonic stages are used to strengthen the ability to cope with mercury stress and attenuate mercury damage. The biochemical parameters, except LSZ, exhibited sensitivity to mercury, suggesting that they may act as potential biomarkers in assessing the environmental mercury risk on C. auratus embryos.