Abstract
The effect of ambient salinity changes (0.9, 6 and 12 psu) on the levels of dissolved ammonia (DA), ninhydrin positive substances (NPS), trimethylamine (TMA) and trimethylamine oxide (TMAO) in the blood and tissue of medium-acclimated
Sander lucioperca L. (also
Stizostedion lucioperca) were investigated. In freshwater, blood and tissue total free amino acid levels (measured as NPS) were 3.62 mM and 60.61 mM, respectively. The NPS content increased significantly (
P<0.05) in the tissue and blood on acclimation to 6 and 12 psu salinities. The mass-specific tissue TMAO concentration of pikeperch acclimated to normal freshwater was 0.413±0.084 μmol TMAO g
−1. Results reveal that TMAO levels are positively influenced by the external salinity medium where significant differences in mean levels occurred between the groups (
P<0.05). The calculated p[NH
3] and [NH
4
+] gradients reveal that the [NH
3] gradient was consistently low (cf. the [NH
4
+] gradient). The gradient of p[NH
3] decreased with the medium increased salinities. The results suggest that freshwater pikeperch may be able to resist salinity changes by manipulation of nitrogen metabolism. Free amino acids and TMAO are involved in mediating response to salinity exposure in freshwater pikeperch.