Effect of mixed protein schedules combined with choline and betaine on the growth performance of Nile tilapia (Oreochromis niloticus) Osama M El-Husseiny, Galal El Din, M Abdul-Aziz & Rania S Mabroke Animal Production Department, Faculty of Agriculture Cairo University, Cairo, Egypt Correspondence: R S Mabroke, Animal Production Department, Faculty of Agriculture Cairo University, Cairo, Egypt. E-mail: raniasms2002@yahoo.com Abstract Reducing feed cost has been a major issue in ¢sh nutrition. Mixed protein schedules have been pro- posed as one of the methods successfully tested in many ¢sh species to reduce feed cost. Meanwhile, the e¡ect of dietary choline and betaine supplemen- tation on ¢sh performance was assessed. The aim of the present study was to investigate the e¡ect of mixed protein schedules, combined with choline and betaine, on Nile tilapia performance. This experi- ment was conducted in a (43) factorial arrange- ment of treatments. Four mixed protein schedules were examined, in the presence of choline 0.3% and/or betaine 0.5%. The four mixed protein sche- dules were achieved by alternating diet (A; 31%CP) and diet (B; 24%CP) as follows: (6 days-A), (5 days-A/ 1day-B), (4 days-A/2 days-B) and (3 days-A/3 days-B). The results indicated that in the presence of betaine 0.5% and choline 0.3%, the optimal mixed protein schedule for tilapia was (3A/3B). Fish fed on the 4A/ 2B or 3A/3B schedules utilized protein more e⁄- ciently than ¢sh fed on the (6A) schedule. Fish fed diets supplemented with betaine (b) only showed the highest energy retention. The lowest feed cost was recorded for ¢sh fed on (3A/3B) in the presence of betaine 0.5% and choline 0.3% in ¢sh diet. Keywords: tilapia, mixed protein schedules, betaine, choline Introduction With the increasing need for cheap sources of protein to meet the overpopulation problem, more attention has been focused on ¢sh farming. Tilapia culture is believed to o¡er one of the solutions. The relative ease of tilapia culture and its rapid growth rate in tropical and semi-tropical climates have led to its distribution worldwide. Such advantages have given tilapia an important edge over other species. China is by far the largest producer of farmed Nile tilapia. Annual Chinese production increased to nearly 806 000 t, followed by Egypt, which produced nearly 200 000 t (FAO 2003). Protein is considered to be the most important component of ¢sh diets (Ste¡ens1981). It is the most expensive component of the diet. De Silva (1985) pos- tulated that the application of a mixed protein sche- dule where a high-protein diet was alternated with alow-protein diet could result in a improvement nutrient utilization.This is because protein digestibil- ity varies on a day-to-day basis in a certain rhythmic manner in Nile tilapia ( Orechromius niloticus ) (De Silva & Perera1984). Application of mixed protein schedules to reduce feed cost and improve nutrient utilization has been demonstrated for Indian carp ( Labeo rohita ) (Nandeesha, Silva & Krishna 1993; Nandeesha, De Silva, Krishnamurthy & Dathatri 1994), common carp ( Cyprinus carpio) under pond culture systems (Nandeesha, De Silva & Krishna- murthy 1995; Nandeesha, Gangadhara & Manissery 2002), Nile tilapia ( O. niloticus ) (Santiago & Laron 2002; Patel & Yakupitiyage 2003; Bolivar, Jimenez & Brown 2006), Channa striata (Hashim 1994), sutchi cat¢sh, silver carp ( Hypopthalmichthys molitrix ) (Ali, Hossain & Mazid 2005) and trout ( Oncorhynchus Mykiss ) (Sevgili, Emre, Kanyilmaz, Diler & Hossu 2006). Betaine [(CH 3 ) 3 N 1 ^CH 2 COO  ] is a non-toxic amino acid derivative widely distributed in nature (Kettunen, Peuranen, Tiihonen & Saarinen 2001). Betaine has many major metabolic functions; it Aquaculture Research, 2008, 39, 291^300 doi: 10.1111/j.1365-2109.2007.01896.x r 2008 The Authors Journal Compilation r 2008 Blackwell Publishing Ltd 291