盐碱胁迫对麦穗鱼的急性毒性及组织结构的影响OA

Salinization of inland water bodies represents a significant and growing global ecological and environmental challenge,particularly in the arid and semi-arid regions of northern China,where intensified lake salinization has led to the widespread degradation of aquatic ecosystems and a decline in fishery resources.Daihai Lake,a representative inland saline-alkaline lake in Inner Mongolia,has undergone continuous and accelerated salinization,resulting in a sharp reduction in aquatic biodiversity.Currently,only a few small fish species persist under these extreme conditions,notably the topmouth gudgeon(Pseudorasbora parva).This species is a eurytopic freshwater fish with a broad environmental tolerance.P.parva survives in Daihai's high-salinity and high-alkalinity waters,indicating strong physiological adaptation.Nevertheless,the physiological and pathological responses of this species to salinity,alkalinity,and their combination remain poorly understood. In the present study,we systematically performed acute toxicity tests to evaluate the interactive effects of salinity and alkalinity on P.parva.Furthermore,histopathological analyses were conducted to assess alterations in key tissues,including the gills,spleen,liver,and intestines.Wild individuals of P.parva were used as the test subjects.After a 7-day acclimatization period,healthy individuals were selected for acute toxicity testing.The experimental design included five salinity groups(3,6,9,12,and 15 g/L NaCl),six alkalinity groups(10,20,40,60,80,and 100 mmol/L NaHCO3),six combined stress groups(3 g/L NaCl+10,20,and 60 mmol/L NaHCO3;9 g/L NaCl+10,20,and 60 mmol/L NaHCO3),and a control group.The experiment was conducted under a semi-static exposure system with triplicates of 10 fish per replicate,during which behavioral responses and mortality were systematically recorded,and LC50 and SC values were calculated.After 96 h of exposure,surviving individuals from the following groups were sampled for histopathological analysis:control,high-salinity(12 g/L NaCl),high-alkalinity(100 mmol/L NaHCO3),and combined stress(9 g/L NaCl+60 mmol/L NaHCO3).Tissue samples from the gills,spleen,liver,and intestines were collected,fixed in 4％paraformaldehyde,embedded in paraffin,sectioned,and stained with hematoxylin and eosin for histopathological examination.The results indicated that P.parva exhibited salinity sensitivity(96-h LC50=8.597 g/L;SC=2.484 g/L).At 15 g/L salinity,the fish exhibited acute stress behaviors characterized by sustained,forceful collisions with tank boundaries and erratic,high-velocity swimming bursts.As the exposure duration increased,behavioral responses progressed to lateral recumbency,accelerated opercular movement(indicative of heightened respiratory demand),and diminished locomotor responsiveness,concomitant with severe pathological signs,including generalized body darkening and subcutaneous abdominal hemorrhage,ultimately leading to 100％mortality.Conversely,P.parva demonstrated exceptional alkalinity tolerance(96-h LC50=146.278 mmol/L;SC=37.149 mmol/L),showing only 20％mortality and mild behavioral anomalies at 100 mmol/L.The combined stress induced synergistic toxicity,resulting in severe tissue damage.Histopathological examination revealed varying degrees of structural injury in multiple tissues.In the gills,high salinity caused filament swelling,along with atrophy and disarray of the lamellae.In contrast,high alkalinity led to a marked increase in the number of chloride cells and extensive epithelial cell shedding.Under combined stress,prominent lamellar detachment and vascular congestion were observed,compromising respiratory and osmoregulatory functions.In the spleen,high salinity induced vacuolation of lymphocytes and a reduction in melanocyte-macrophage centers,whereas high alkalinity led to an increase in lymphocyte numbers and an expansion of the white pulp area.Under combined stress,prolonged immune cell dissolution and degeneration of the splenic medulla were observed.In the liver,saline-alkaline stress induced hepatocyte vacuolation,nuclear displacement,sinusoidal dilation,and inflammatory cell infiltration,and the most severe damage was observed under combined stress,which potentially impaired energy metabolism and detoxification functions.In the intestinal mucosa,both high salinity and alkalinity caused atrophy of the mucosal folds and disorganization of epithelial cells.Although combined stress induced some adaptive morphological changes in the mucosal folds,epithelial cell shedding remained evident,suggesting impaired digestive and barrier functions. In summary,the present study characterized the physiological traits of P.parva,revealing its sensitivity to salinity and high tolerance to alkalinity.The findings demonstrate that combined saline-alkaline stress exerts synergistic toxic effects and,based on histopathological evidence,elucidate the structural damage mechanisms in various organs.These results provide a theoretical foundation and practical reference for further elucidation of the saline-alkaline tolerance mechanisms of P.parva and for guiding the ecological restoration of salinized aquatic systems.