Growth, stress response and free amino acid levels in Senegalese sole (Solea senegalensis Kaup 1858) chronically exposed to exogenous ammonia

Stressful husbandry conditions are likely to affect growth and amino acid metabolism in fish. In this study, chronic ammonia exposure was used to test the effects of a stressor on growth and amino acid metabolism of Senegalese sole juveniles. The fish were exposed for 52 days to 11.6 mg L-1 [low-TAN (L-TAN)] or 23.2 mg L-1 [high-TAN (H-TAN)] of total ammonia nitrogen (TAN), or to 0 mg L-1 (Control). Growth in L-TAN groups was slightly but significantly different from the Control groups [relative growth rate (RGR=0.35 +/- 0.13 and 0.52 +/- 0.23% day(-1) respectively)]. In H-TAN groups, growth was severely affected (RGR=0.01 +/- 0.13% day(-1)). Stress parameters (plasma cortisol and glucose) showed slight or no significant differences between treatments. Plasma free amino acid (FAA) concentrations were affected after H-TAN treatment. Increases in glutamine and aspartate concentrations in H-TAN fish suggest alterations in amino acid metabolism related to nitrogen excretion processes. Some of the changes in FAA concentrations also suggest mobilization to energy supply and synthesis of metabolites related to stress response. Therefore, Senegalese sole seem to adapt to the L-TAN concentration tested, but the H-TAN concentration reduced growth and affected amino acid metabolism.