Effects of chronic and periodic exposure to ammonia on growth and blood physiology in juvenile turbot (Scophthalmus maximus)

Juvenile turbot (Scophthalmus maximus) were exposed periodically and chronically to different levels of un-ionised ammonia (UIA-N) and the subsequent effect on growth and food conversion efficiency was studied. Fish with a mean (SD) initial weight 19.3 (3.9) g, were exposed to five treatments consisting of a control group, two groups (ChronicLow and ChronicHigh, UIA-N levels of 0.13 and 0.25 mg l- 1, respectively) chronically exposed to ammonia and two groups (LowPulse and HighPulse) exposed to the same levels as above for a short period daily. The fish were held for 64 days at 18 °C, a pH of 8.04 and a salinity of 33.5‰. At the end of the experiment, fish from the Control group had a significantly higher mean weight (95.5 g) compared to all other groups. Fish from the ChronicHigh group displayed the lowest mean weight (74.6 g), whereas fish in the ChronicLow, LowPulse and HighPulse groups displayed mean weights of: 79.3 g, 82.8 g and 81.9 g, respectively. Blood ion concentrations were not affected significantly in any of the treatments, whereas minor reductions in blood pH, partial pressure of CO2 and total CO2 content were found in ammonia exposed groups up until day 44 of the experiment. Feed conversion efficiency, daily feeding rate and total feed consumption did not vary significantly between treatments. The study demonstrate that short daily ammonia peaks may result in negative effects on growth, equivalent to that found under chronic ammonia exposure in juvenile turbot.