Effects of salinity stress on the growth performance, histological characteristics, and expression of genes related to apoptosis and immunity in channel catfish (Ictalurus punctatus).

Salinity is an important environmental factor affecting fish growth and development. To investigate the effects of salinity stress on the growth performance, tissue structures, and expression of genes related to apoptosis and immune response in large-sized channel catfish (Ictalurus punctatus) juveniles, an 8-week salinity stress experiment was conducted. Six salinity levels (3, 3.8, 4.7, 5.9, 7.3, and 9 psu) were set according to an equal logarithmic concentration gradient method, along with a control group (0), and growth performance and physicochemical indices were measured. The survival rate of channel catfish in all salinity groups was 100%. Body length, body weight, weight gain rate, and specific growth rate decreased with increasing salinity, with higher salinity levels resulting in more significant reductions in growth performance. At 9 psu, both the specific growth rate (SGR) and weight gain rate (WGR) decreased significantly to 0.61%/day and 40.86%, respectively (p < 0.05). Histological analysis results indicated that with the increase in salinity, the number of intestinal mucosal folds relatively increased, while the number of goblet cells gradually decreased. Hepatocytes became more densely packed, and the hepatic lobule gaps widened. Apoptosis detection results revealed that in the liver, the number of apoptotic cells at 4.7 psu salinity was more than that in the control group and at 9 psu salinity. In the intestine, the number of apoptotic cells at 9 psu salinity was significantly higher than in the other two groups (p < 0.05). Quantitative polymerase chain reaction (qPCR) analysis of the expression patterns of genes related to apoptosis and immunity showed that the expression levels of caspase 3, caspase 8, INF-I, IL-1β, and bax genes in the liver and intestinal tissues were higher in the experimental groups than in the control group, while the expression of bcl-2 decreased with increasing salinity in liver tissue but increased in intestinal tissue. These findings can provide theoretical guidance for the aquaculture of channel catfish in saline-alkali land.