Effect of density stress on the physiological, biochemical, and immunological parameters of juvenile Pelteobagrus fulvidraco during simulated transportation

Live fish transport is an important aspect of aquaculture, especially at high densities, which might cause considerable stress and compromise product quality. This study investigated the effects of transport density and time on stress responses, innate immunity, and immune gene expression in juvenile yellow catfish. The fish were designated to five density groups: D11, D12, D13, D14, and D15 (500, 333, 250, 200, and 167 kg/m3). After 36 h of transport, only the D15 group had a 100% survival rate, followed by D14 with 83% survival, and 0% in the remaining three density groups. The damage to gill filaments and the liver worsened with increasing environmental stress severity. The results showed that with the prolonged transport time, plasma cortisol (COR), and catalase (CAT), malonaldehyde (MDA) and lysozyme (LZM) levels in the livers first increased and later gradually decreased after 16 h of transport, while the activity of superoxide dismutase (SOD) continued to rise. The activities of CAT and MDA content increased as the density increased. The expression of heat shock protein (HSP) 70 and 90, tumor necrosis factor α (TNF-α), and interleukin-1β (IL-1β) in juvenile livers in D11 group was significantly higher than the control group (p < 0.05), confirming that density imposed stress on fish during transport. In conclusion, we demonstrated that increased density and time during live transport induced significant physiological stress responses in juvenile P. fulvidraco. This study provides insights into the transport of yellow catfish to improve transport measures and reduce economic losses to the aquaculture industry.