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±0.3°C. 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 relat- ed to the protein quality of these species which may be higher than that of the anchovy for tur- bot nutrition.