Ammonia nitrogen excretion rate - An index for evaluating protein quality of three feed fishes for the black sea turbot

Abstract

Total ammonia nitrogen excretion rates were measured in young Black Sea turbot (74.79 g avg wt) reared in brackish water (17 ppt salinity) at 11+/-0.3degreesC. Duplicate groups of turbot were fed a fixed quantity of teleosts, either anchovy (Engraulis encrasicolus), goby (Gobius sp.) or whiting (Merlangius merlangus). Feeds were offered to the turbot as wet feed. Cumulative ammonia-N excretion over a 6-hour period was significantly lower (p<0.05) in fish fed goby (3.64+/-0.27 mg-N/100 g fish) and whiting (3.83+/-0.13 mg-N/100 g fish) than that in fish fed anchovy (4.48+/-0.06 mg-N/100 g fish). The ammonia-N excretion rate in all groups peaked two hours after feeding, but the peak value in the group fed anchovy was significantly higher (p<0.05) than in the other two groups. No differences were observed among diets in samples taken 3, 4, 5 and 6 hours after feeding. Significantly lower excretion levels in the goby and whiting groups could be related to the protein quality of these species which may be higher than that of the anchovy for turbot nutrition.