低盐胁迫致大菱鲆体色异常的组织学和生理学分析OA

Turbot(Scophthalmus maximus)is a commercially important aquaculture species in China.As farming expands into coastal mudflats and inland regions,the breeding of varieties with enhanced low-salinity tolerance has become critical.However,the lack of efficient and quantifiable phenotypic markers for stress resistance remains a major bottleneck.Previous studies observed that juvenile S.maximus exposed to extreme low-salinity stress(0)exhibit a consistent and reversible pattern of abnormal coloration:transitioning from the appearance of black stripes(termed the"qingsi"period)to a regionalized mosaic pattern of darkening and blanching(termed the"shikong"period).Notably,coloration reverts to normal upon return to seawa-ter,even in near-moribund individuals.This phenomenon suggests that the chromatic response is intrinsically linked to physiological tolerance and may serve as an intuitive phenotypic marker for low-salinity resilience.To investigate the underly-ing mechanisms,this study subjected fish to 0(low salinity)and 30(control)environments.The low-salinity group was further stratified into"color-changing"and"color-maintaining"subgroups based on their phenotypic response.During a one-week stress-recovery experiment,body color dynamics and melanophore morphology were systematically monitored through histological observation.Concurrently,serum levels of key hormones—including norepinephrine(NE),epinephrine(E),α-melanocyte-stimulating hormone(α-MSH),melanin-concentrating hormone(MCH),acetylcholine(ACh),and thyroid hor-mones(T3,T4,fT3,fT4)—were quantified using ELISA analysis.Results showed that control fish maintained normal color-ation and melanophore morphology(partially dispersed state)throughout the experiment.Under low-salinity stress,the color-maintaining group showed no significant differences in coloration or melanophore morphology compared to controls.Conversely,the color-changing group exhibited dynamic transitions:from normal coloration to black stripes,followed by a mosaic pattern,and finally reverting towards normal upon seawater restoration.Melanophore dynamics mirrored these changes:during the"qingsi"period,melanophores were fully dispersed in black stripes but partially dispersed in normal areas;in the"shikong"period,melanophores were fully dispersed in darkened regions and completely aggregated in blanched areas.Hor-mone analysis revealed that NE,E,and α-MSH levels in the color-changing group exhibited a dynamic pattern:rising gradu-ally during the stress period,peaking at the"shikong"period,and subsequently declining to near-baseline levels during the recovery period.Specifically,concentrations of these three hormones were significantly elevated in the color-changing group compared to both the control and color-maintaining groups during the"shikong"period(P<0.05).At the"qingsi"period,NE and α-MSH levels remained significantly higher in the color-changing group(P<0.05).Levels in the color-maintaining group were generally intermediate between those of the color-changing and control groups.In contrast,other endocrine indicators(MCH,T3,T4,fT3,fT4,and ACh)showed minimal fluctuations under low-salinity stress,with no significant differences or clear trends observed across groups.These findings suggest that low-salinity stress induces abnormal coloration through melan-ophore alterations driven by the interplay of NE,E,and α-MSH.This study provides new insights into stress physiology and highlights these color-associated hormones as key potential indicators for cultivating new aquaculture varieties with enhanced low-salinity tolerance.