Effects of Density Stress During Transportation on the Antioxidant Activity and Immuno-Related Gene Expression in Yellowfin Seabream (Acanthopagrus latus Houttuyn, 1782).

Background/Objectives: Maintaining an optimum transport density is essential for protecting water quality, lowering stress levels, and increasing fish survival rates. Transporting marine fish fry involves major dangers. The purpose of this study was to evaluate the impact of transport stress at varying densities on the immune-related gene expression, antioxidant capacity, and survival rate of yellowfin seabream (Acanthopagrus latus) fry. Methods: A 12 h simulated transport experiment was conducted with A. latus fry divided into six density groups. For 1-2 cm fry, densities of 900, 1200, and 1500 fry per pouch were used to assess antioxidant enzyme activity; and for 4-5 cm fry, densities of 100, 125, and 150 fry per pouch were used for gene expression analysis. The key parameters measured included survival rates, antioxidant enzyme activities in liver and intestinal tissues, and expression levels of HSP90α and caspase-3 genes. Results: The findings showed that recovery time and density both affected the observed responses and that transport density had a substantial effect on antioxidant enzyme activity in all tissues. The intestinal and liver tissues showed a considerable decrease in antioxidant enzyme activity, suggesting that these tissues may be able to respond to oxidative stress. Moreover, under high-density transport conditions, there were notable increases in the expression of caspase-3 and HSP90α, suggesting the activation of immune response systems. This research offers valuable new understandings into the relationship between transport density and immunological and antioxidant modulation in A. latus fry. Conclusions: The results provide a scientific foundation for enhancing aquaculture transport conditions, which will ultimately lead to decreased fish mortality and improved general health during transit, resulting in more sustainable and effective aquaculture methods.