Insight into critical water quality factors and gill function of large yellow croaker (Larimichthys crocea) during packaging bag transport

To investigate the effects of the interaction between water quality and gill function of large yellow croaker during transportation in packaging bags, a total of 186 large yellow croakers weighing 120.0 ± 28.0 g were randomly divided into two groups: a control group (tanks with a water treatment system to maintain normal water quality) and treatment groups subjected to simulated transport for 0, 6, 12, 18, and 24 hours at a temperature of 20°C. The results revealed that prolonging the transport duration (beyond 6 hours) caused significant changes in dissolved oxygen (DO), total ammonia nitrogen (TAN) and pH levels in the water. Beyond 6 hours of transport, gill tissue damage increased, and the histomorphological characteristics of the gills were altered. Regarding osmoregulation, the activities of Ca 2+ /Mg 2+ -ATPase and Na + /K + -ATPase were notably reduced in the treatment groups, indicating compromised osmoregulatory function of the gill tissue during transport. However, changes in lactic acid (LD) and lactate dehydrogenase (LDH) were not statistically significant, and fish did not experience hypoxia during packaging bag transport. In terms of antioxidant activity, the treatment groups exhibited significantly lower activities of catalase (CAT) and superoxide dismutase (SOD) after 24 hours, as well as increased malondialdehyde (MDA) content after 18 hours. This reduction in antioxidant capacity led to cellular membrane damage in the gill tissue. Furthermore, acid phosphatase (ACP) activity showed a notable decline from 12 hours onwards in immune indicators, while lysozyme (LZM) activity experienced a substantial decrease at 24 hours. Correlation analysis revealed a significant correlation between the osmoregulation, antioxidant capacity, and immune response of gill tissue with elevated TAN levels and reduced pH. In conclusion, the levels of TAN and pH experience notable alterations after 6 hours of transportation, which may lead to impairment of gill function in large yellow croakers. Hence, we advise limiting the transportation of large yellow croakers to less than 6 hours at 20°C. • The TAN and pH are key factors affecting the transport of large yellow croaker in packaging bags. • The activities of Ca 2+ /Mg 2+ -ATPase and Na + /K + -ATPase are significantly reduced during transport. • DO levels are sufficient, and large yellow croakers are not affected by hypoxia. • The transport influences the antioxidant and immune capacity of gill tissue in the large yellow croaker.