急性酸化胁迫和恢复对虹鳟与硬头鳟生理生化响应的影响OA

Within intensive high-density recirculating aquaculture operations,abrupt declines in water pH,often stemming from excessive stocking densities,unbalanced feeding protocols,and the uncontrolled application of chemical additives,pose critical risks to fish health and compromise the sustainability of the system.Acute acidification episodes destabilize the aquatic milieu,disrupt endocrine regulation,and cause extensive metabolic perturbations.In China,landlocked rainbow trout(Oncorhynchus mykiss)and anadromous steelhead trout(O.mykiss),which have two distinct life history strategies within the same species,have become the principal salmonid species cultured in offshore marine aquaculture.These ecotypes exhibit marked differences in physiological plasticity,including thermal tolerance,osmoregulatory capacity,and hypoxic resilience,which likely underpin their distinct responses to acidification stress.Teleosts have evolved intricate physiological adaptations to counteract environmental acidification,with the antioxidant defense system playing a central role.Therefore,we systematically compared the physiological and biochemical responses of rainbow and steelhead trout to acute acidification stress.Three experimental pH gradients(6.5,6.0,and 5.5)were established using a controlled chemical acidification protocol(37％hydrochloric acid:sodium bicarbonate=1 mL:0.45 g),with pH 8.0 serving as the control.Results showed that acidification significantly influenced hepatic superoxide dismutase(SOD)and malondialdehyde(MDA)levels,serum alkaline phosphatase(AKP),branchial Na+/K+-ATPase and Mg2+-ATPase,as well as intestinal amylase(AMS)and trypsin(TPS)activities in both ecotypes.At pH 6.0,rainbow trout exhibited significantly higher hepatic SOD,MDA,serum AKP,branchial Na+/K+-ATPase,Ca2+-ATPase,and Mg2+-ATPase activities compared to other treatment groups(P＜0.05),whereas their intestinal AMS and TPS activities were significantly lower at pH 5.5(P＜0.05).At pH 5.5,steelhead trout exhibited significantly higher hepatic SOD and MDA levels,serum AKP,branchial Na+/K+-ATPase and Mg2+-ATPase activities compared to other treatment groups(P＜0.05).Conversely,their intestinal AMS and TPS activities were significantly elevated at pH 8.0 and 6.5,relative to other treatments(P＜0.05).At pH 6.0,significant differences(P＜0.05)were observed in rainbow trout between 12 h and 24 h of the recovery period in hepatic SOD,MDA,serum acid phosphatase(ACP),AKP,branchial Na+/K+-ATPase,intestinal lipase(LPS),and TPS activities.At pH 5.5,significant differences(P＜0.05)were detected between the two recovery durations for rainbow trout serum AKP activity and steelhead trout hepatic SOD,serum ACP,AKP,branchial Na+/K+-ATPase,and intestinal LPS activities.Collectively,rainbow trout exhibited the most pronounced responses at pH 6.0,with most parameters returning to baseline after recovery,whereas steelhead trout exhibited the strongest stress response at pH 5.5.Significant interaction effects between species and acidification levels were observed for hepatic SOD,MDA,catalase(CAT),branchial Na+/K+-ATPase,Ca2+-ATPase,Mg2+-ATPase,and intestinal AMS,LPS,and TPS activities(P＜0.05).Principal component analysis revealed that different pH treatments significantly altered the overall physiological and biochemical states of both ecotypes,with distinct clustering patterns between the two species.Collectively,these findings indicated that landlocked rainbow trout are more vulnerable to acute acidification stress,whereas anadromous steelhead trout possess greater physiological resilience in acidic environments.These findings provide theoretical insights into the environmental adaptation mechanisms of salmonids with divergent life history strategies and inform aquaculture management practices in acidified water systems.Implementing pH buffering strategies at ≥6.5 could mitigate stress in rainbow trout systems,whereas steelhead trout cultures may tolerate brief exposures to pH 5.5 with appropriate recovery intervals.