Department of Fishery Science, Faculty of Natural Resources, Lahijan Branch, Islamic Azad University, Lahijan, Iran.
This study was conducted in two stages. At the first stage, the lethal concentrations (LC50 96h) of ammonia in different salinities including, 0ppt (7.42 mgL-1), 4ppt (8.24 mgL-1), 8ppt (9.60 mgL-1) and 12 ppt (10.22 mgL-1) to A. stellatus fingerlings were determined. At the second stage, 240 fish (15.23±2.17 g, mean weight and 17±1.96 cm, total length) were exposed to half (50%) median lethal concentration (LC50 96h) under the same salinities for four days (8 treatments in triplicates). Maximum Red blood cells , white blood cell , hematocrit , hemoglobin, mean corpuscular volume , mean corpuscular hemoglobin , mean corpuscular hemoglobin concentration , and differentiation of leucocytes indices were observed in combined treatments (salinity with ammonia) with salinity and ammonia (p≤0.05). Cortisol, glucose, and lactate decreased, meanwhile immunoglobulin M, lysozyme and total immunoglobulin blood serum levels significantly increased with increasing salinity and ammonia in combination treatments (p≤0.05). The activity of superoxide dismutase and glutathione peroxidase blood serum increased in combined salinity and ammonia treatments but catalase decreased significantly (p≤0.05). Alanine aminotransferase and aspartate aminotransferase enzyme levels increased in combined salinity and ammonia treatments (p≤0.05). But a significant decrease in the levels of alkaline phosphatase and lactate dehydrogenase blood serum enzymes was observed (p≤0.05). The highest gill and liver damage was observed in salinity of 12 ppt and also combined treatment of salinity of 12 ppt with ammonia. The highest hepatic P450 gene expression was observed in the last treatment (p≤0.05). As a result, increasing salinity increasing tolerance, reduced stress and increasing immunity in stellate sturgeon fingerlings at higher concentrations of ammonia. But salinity could not reduce the toxic effects of ammonia on other indicators.