Using ammonia nitrogen excretion rates as an index for evaluating protein quality of prawns in turbot (Psetta maeotica) nutrition

Total ammonia nitrogen excretion rates were measured in Black Sea turbot (averaging 88.8 g) to compare the protein quality of prawns, the natural food of turbot, with that of the protein source commonly used in the feed industry, i.e. anchovy meal. Two different prawn species (Baltic prawn, Palaemon adspersus, and rockpool prawn, Palaemon elegans) were offered to fish as wet feed at 17.5 - 0.5 …C and a salinity of 17 ppt. Furthermore, for determination of the effects of wet feed and dry feed on the peak times of ammonia nitrogen excretion rates, another experimental group of fish was offered a commercial dry diet with anchovy meal as a single protein source. The ammonia nitrogen excretion rate in both groups fed prawns peaked 3 h after feeding, while the peak of the excretion rate of fish fed the dry diet was delayed up to 6 h after feeding. Cumulative ammonia nitrogen excretion rates as well as the excretion as a proportion of ingested nitrogen were significantly lower (P < 0.05) in fish fed prawns than those in fish fed the dry diet. Significantly lower excretion levels in the prawn groups might be a reflection of the protein quality of these species, which may be higher than that of the anchovy meal for turbot nutrition. Ozet: Kalkan bal›¤›n›n doal besinini oluflturan karideslerin protein kalitesi ile yem sektorunde yayg›n kullan›lan hamsi ununun protein kalitesinin karfl›laflt›r›lmas› amac›yla, Karadeniz kalkan bal›klar›nda (ortalama 88,8 g) total amonyak nitrojen boflalt›m oranlar› belirlenmifltir. Bal›klar, 17,5 - 0,5 …C ve ‰ 17 tuzluluk ortam›nda iki farkl› karides turu (Balt›k karidesi, Palaemon adspersus ve rockpool karides, Palaemon elegans) ile yemlenmifltir. Ayr›ca taze yem ile kuru yemlerin amonyak nitrojen boflalt›m oranlar›n›n maksimuma ulaflma sureleri uzerine etkilerinin de belirlenmesi amac›yla, dier bir deneme grubuna, protein kayna¤› olarak hamsi unu iceren kuru yem verilmifltir. Her iki karides grubundaki amonyak nitrojen boflalt›m oranlar›, yemlemeden uc saat sonra en ust duzeye ulafl›rken, kuru yemle beslenen bal›klardaki boflalt›m oran›n›n maksimuma ulaflma suresi alt› saate kadar uzam›flt›r. Kumulatif amonyak nitrojen boflalt›m oranlar› ve boflalt›m miktarlar›n›n tuketilen nitrojene oran›, karides ile beslenen bal›klarda kuru yemle beslenen gruptaki oranlardan istatistiksel olarak daha dufluk (P < 0,05) kaydedilmifltir. Karides gruplar›ndaki boflalt›m oranlar›n›n onemli derecede dufluk olmas› ile, kalkan beslenmesinde bu turlerin protein kalitesinin hamsi ununa oranla daha yuksek olduu sonucuna var›labilir.