WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2015 43 Tilapia has drawn much attention lately and been recognized by the FAO as the cultured fish species with the greatest potential to supply human protein this century. Production of tilapia has been increasing throughout the world and a future increase in production has been projected. As the industry expands and technology development continues, traditional extensive culture of tilapia is being replaced by semi-intensive and intensive production systems. As stocking rates increase, the contribution of natural food decreases and more nutritionally complete diets are needed. In semi-intensive and intensive culture systems, feed is the most expensive cost item, often ranging from 30 to 60 percent of total variable costs, depending on production intensity. Thus, the use of least-cost, nutritionally-balanced feeds and good feeding practices are two of the most important requisites for economically successful semi-intensive and intensive aquaculture. Traditionally, dietary non-protein energy sources, such as carbohydrate or lipid, spare protein for growth (Shiau 2002). However, the common carbohydrate sources also have poor digestibility because fiber content is high. Feeds with a high lipid content causes fatty fish. Therefore, feed additives that improve nutrient utilization have potential to promote protein sparing in tilapia and reduce the feed cost per unit fish and/or fillet produced. Synergistic blends of digestive phytobiotics, natural emulsifying agents and co-factors of fat digestion have potential to improve feed efficiency and growth and to reduce visceral fat deposition in Nile tilapia under lab and field conditions (Ceulemans et al. 2009, Sampaio Gonçalves et al. 2012). We investigated the effects of a feed additive with digestive/ metabolic enhancing effects with a reduction in reduce dietary protein level on growth performance and product quality of tilapia. During the trial, fish growth performance, fillet yield, metabolic indicators, lipid utilization and intestinal morphology were evaluated. Effects of the Feed Additive on Growth Experimental diets were designed by National Pingtung University of Science and Technology (NPUST) based on a common feed formulation for tilapia in Taiwan (Table 1). Diets were extruded by Tungkang Biotech Research Center (Pingtung, Taiwan). The feed additive with digestive/metabolic enhancing properties was Aquagest® OMF (Nutriad International, Belgium). Experimental diets consisted of a control diet (28 percent protein and 7 percent lipid, coded as CONTROL 28/7) and a test diet containing 2 percent less protein and with 0.3 percent Aquagest® OMF feed additive (26 percent protein and 7 percent lipid, coded as LOPRO 26/7+AG). Male hybrid tilapia (Oreochromis niloticus × O. aureus) were supplied from a farm in Tainan, Taiwan and reared in Changjhih, Pingtung. Prior to feeding test diets, tilapia were acclimated to farm conditions for two months in a concrete tank (5 m W × 5 m L × 0.75 m deep) and fed a commercial tilapia feed (Hanaqua Tech Inc., Taiwan). Conditions during the acclimation period were similar to those at the initiation of the experiment. Three concrete tanks were used for the feeding trial. Each tank was divided in two by a nylon net. Forty-five tilapia with average initial weight of approximately 175 g were randomly Stimulating Protein Sparing in Tilapia Through Digestive/Metabolic Enhancement Yu-Hung Lin and Allen Ming-Hsiun Wu (CONTINUED ON PAGE 44) FIGURE 1. Collection of the fillet and visceral fat of tilapia in Hung-Yi Frozen Food Factory, Pingtung, Taiwan.
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