G.R. Rafiei
C.R. Saad
M.S. Kamarudi
M.R. Ismail
S.M.H. Alavi

A completely randomized experimental design was conducted to estimate ammonia excretion rate by red tilapia (Oreochromis sp.) during different stages of its growth in recirculating water system units typically designed to meet the experiment purposes. Eight weight groups each containing ۷۵individuals of ۲۰, ۳۰, ۴۰, ۶۰, ۸۰, ۱۲۰, ۱۸۰ and ۲۰۰g average weight were considered as treatments in duplicates. The rate of ammonia excretion by each fish group was measured during a ۲۴-hr period. The data was extended to estimate total ammonia excreted by a group of red tilapia during a ۱۱۵-day culture period (۲۰-۲۰۰g). The mean daily ammonia excretion rate was significantly different between treatments (p<۰.۰۵). These rates were ۳۴.۰۶±۱.۲۳, ۳۲.۵۶±۳.۲۸, ۲۷.۰۶±۰.۸۷, ۱۷.۴۶±۲.۱۹, ۱۲.۵۴±۱.۳۰, ۱۲.۴۸±۱.۴۱, ۷.۸۷±۱.۸۲ and ۵.۸۳±۰.۱۹ mg kg fish-۱ h-۱ for ۲۰, ۳۰, ۴۰, ۶۰, ۸۰, ۱۲۰, ۱۸۰ and ۲۰۰ g fed fish, respectively. It was estimated that on average ۳۹.۴% of input feed nitrogen excreted as ammonia-N during the culture period. Results of this study well addressed the regime of ammonia production in different stage of red tilapia growth in a recirculating water system.

Body weight, Ammonia excretion, Red tilapia, Recirculating water system