Structural Adaptations to Saline Stress: Histomorphological Changes in the Osmoregulatory and Metabolic Organs of Perca schrenkii Under Acute and Chronic Challenges

The escalating scarcity of freshwater resources necessitates the utilization of alternative saline waters for sustainable aquaculture. <i>Perca schrenkii</i>, an endemic fish from the Ili River basin, demonstrates considerable potential for cultivation in chloride-type saline-alkaline waters: its 96 h acute salinity tolerance is higher than that of freshwater populations of its congeneric <i>Perca fluviatilis.</i> This study systematically investigated the histomorphological responses of its key osmoregulatory and metabolic organs-gill, kidney, intestine, and liver-under acute (12-14 ppt for 96 h) and chronic (3-7 ppt for 60 days) salinity stress. Acute exposure induced dose- and time-dependent structural damage, including lamellar fusion in gills, glomerular reduction in kidneys, mucosal atrophy in intestines, and hepatocellular swelling. In contrast, chronic acclimation revealed active remodeling, such as lamellar shortening, renal tubular dilation, intestinal muscularis thickening, and biphasic hepatocyte adjustments. A hierarchical framework of structural adaptation was proposed, delineating Safe (≤3 ppt), Acclimation (5 ppt), Tolerance (7 ppt), and Lethal (≥13 ppt) zones. These findings elucidate the structural basis of salinity tolerance in <i>Perca schrenkii</i> and provide practical morphological indicators for assessing fish health in saline aquaculture.