الفهرس 
ITRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 152 |  |  |
| | | from | 152 | | |
Abstract
Tilapia culture has sharply expanded throughout the world during the past two decades. Production systems of tilapia have also witnessed a rapid industrialization during this period. As a result, the global production of farmed tilapia has increased from 383,654 metric tons (mt) in 1990 representing 4.5% of total farmed fish production to 3,497,391 mt in 2010, representing 8.9% of total farmed fish production, with an average annual growth of 13.5% (FAO, 2012). Unfortunately, intensive aqua-farming is accompanied by several problems where infectious diseases come first in limiting the production with consequent negative impact on growth. One of the main challenges to achieve productive, feasible and sustainable aquaculture is to develop alternative preventive practices that may help to maintain high animal welfare standards as well as healthy environment, resulting in a better production and higher profits. Application of probiotics and prebiotics (synbiotics) for aquatic animals improves welfare and promote growth (Rishi et al., 2009 and Dimitroglou et al., 2011). Probiotic and prebiotic are a live microbial feed supplements and a non-digestible food ingredient, respectively. Many published reports demonstrated positive effects of probiotics and prebiotics in feeding of various fish species (Denev et al., 2009). Several probiotic strains have been used to enhance fish survivorship and growth (Suzer et al., 2008; Tovar-Ramirez et al., 2004) with several Lactobacillus species showing beneficial effects in fish juvenile husbandry (Balcázar et al., 2007a). Examples of prebiotics include mannan oligosaccharides, lactose, galacto-gluco-mannans, oligofructose, and inulin. Many of these prebiotics are carbohydrates, primarily short-chain oligo¬saccharides consisting of three to ten carbohydrate units (Gatlin III and Peredo, 2012). Synbiotic is defined as a combination of probiotic and prebiotic. It is presumed to impart the beneficial effects of both ingredients. Few data are available regarding the application of synbiotics in aquaculture (Daniels et al., 2010; Li et al., 2009; Rodriguez-Estrada et al., 2009; Zhang et al., 2010). Synbiotics can help to improve health status, disease resistance, growth performance, feed utilization, carcass composition, gastric morphology, digestive enzyme activities, antioxidant enzyme activities and gene expression. As such; many commercial dietary formulations now routinely include probiotics or prebiotics. In the short- to medium- term future, the full economic implications of these feed additives will become apparent (Merrifield, 2012). The aim of the present study was to study the effects of individual and combined supplementation of a potential probiotic (Bcillus licheniformis) and the prebiotic yeast extract on growth performance, chemical composition, hematological parameters and blood parameters of Nile tilapia (O. niloticus).