Interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus)

The present study was to investigate the interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus). The fish were exposed to four total ammonia nitrogen (0, 5, 20, 40 mg/L TAN) and two stocking density. After 96 h of exposure, blood, gill, and liver samples were collected to measure biochemical parameters and mRNA levels of immune-related genes. The results showed that co-exposure to high TAN (20 and 40 mg/L) and high density significantly increased plasma sodium (Na⁺), gill Na⁺/K⁺-ATPase activity and mRNA levels. Following individual and combined exposure to high TAN and high density, the heat shock protein 70 (HSP 70), HSP 90, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) genes expression were obviously higher than their control. Conversely, the lysozyme (LZM) and hepcidin mRNA levels were down-regulated in liver of fish exposed to high TAN alone and combination of high TAN-density. Moreover, glutathione S-transferase (GST) mRNA levels significantly increased in treatments with individual high TAN and high density, but decreased in high TAN-density co-exposed fish. Overall, ion homeostasis and immune status were adversely influenced in high exposed turbot under high density.