SUBLETHAL EFFECTS AND SAFE LEVELS OF AMMONIA IN SEAWATER FOR ATLANTICSALMON POSTSMOLTS (SALMO-SALAR L)

Atlantic salmon postsmolts (0.6-0.7 kg) were exposed to four different concentration intervals of un-ionized ammonia nitrogen (NH3-N) and to tal ammonia nitrogen (TAN = NH4+-N + NH3-N) in an open flow system: 0. 2-3 mu g/litre NH3-N and 0.02-0.25 mg/litre TAN (control), 9-17 mu g/l itre NH3-N and 1.12-1.41 mg/litre TAN(low), 14-32 mu g/litre NH3-N and 1.80-2.70 mg/litre NH3-N (medium), and finally 43-80 mu g/litre NH3-N and 5.50-6.70 mg/litre TAN (high). The water temperature was 8-9 degr ees C and the salinity was 34-35 parts per thousand. After I month the mean plasma glucose levels were significantly increased both for the medium and the high ammonia group when compared to control. However, t he increase was small and the mean plasma glucose values were consider ed to be in the normal range for Atlantic salmon postsmolts for all gr oups. No significant differences were found in hematocrit, in plasma c hloride in the growth parameters (weight, length and condition factor) and no differences were observed in the gill epithelium of the groups . The exposure period was only I month and further research is needed to study safe levels of ammonia for Atlantic salmon postsmolts. In suc h studies plasma glucose seems to be an important parameter to measure . However, under less controllable conditions other factors than ammon ia may increase the plasma glucose level.