الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The use of feed additives as natural growth promoters has received considerable attention in the aquaculture industry. In the field of aquaculture it is well established so far that the inclusion of antibiotics into the diets of fish can promote growth and feed conversion (Ahmed and Matty, 1989). Although antibiotic growth promoters in fish diets promote growth and improve feed conversion and survival rates, public concern over cross-resistance to human led to a ban on the use of such substances (Cuvin-Aralar et al., 2011). Due to the above mentioned facts alternatives needed to be found. In recent years there has been considerable interest in finding or developing alternatives to antibiotic growth promoters.The introduction of organic acids as an alternative to antibiotics in fish feed may present an interesting alternative (Lückstädt, 2008 b). Organic acids are an example of a group of additives which can play an important role in future in aquaculture diets. A number of studies, in cold-water fish species (Gislason et al., 1994 and 1996) and tropical fish species (Xie et al., 2003, Ramli et al., 2005 and Petkam et al., 2008), indicated that a broad range of organic acids, their salts or mixtures can improve growth, feed utilization and disease resistance in fish. Acidifiers in animal feed were initially used in piglets to compliment their limited capacity to maintain a low gastric pH, which linked to problems with digestion (Easter, 1988). Antibiotic inhibit all microbial growth (Cromwell, 1990), whereas acidifiers are more selective in their activity. They can reduce harmful micro-organisms and promote beneficial microflora colonization of the gastrointestinal tract (Mathew et al., 1991). An important objective of dietary acidification is the inhibition of intestinal bacteria competing with the host for available nutrients and reduction of toxic bacterial metabolites like ammonia and amines, thus improving the weight gain of the target animal. Furthermore, the growth inhibition of potential pathogenic bacteria and like E. coli, Vibrio and Salmonella, both in the feed and in the gastrointestinal tract, has a clear benefit to animal health (Baruah et al., 2008).A decrease in total aerobes and E. coli was also observed by feeding citric acid to weanling pigs. Beside these, gastric acidity enhances solubility of minerals in the gastrointestinal tract and utilization by animals. This is beneficial for a gastric fishes like cyprinids, as better absorption of Ca and P takes place in acidic condition. Baruah et al., (2007) reported increased mineral availability in Labeo rohita fed plant-based diets. An increase in the apparent availability of Ca, P, Mg, Mn and Fe in rainbow trout fed fishmeal-based diets supplemented with citric acid has also been reported.The present study was designed to investigated the effect of some organic acids (1:1 malic+oxalic acids blend) and organic acid salts (1:1 Na-acetate+Ca-lactate blend) at increased levels (0, 0.5, 1.0 and 1.5% of these blends) on the growth performance, feed utilization, proximate analysis and some hematological aspects of Oreochromis niloticus.