JOURNAL OF THE WORLD AQUACULTURE SOCIETY Volume zy 36, No. z 1 March 2005 Effect of Dietary Lipid Level and Protein Energy Ratio on Growth and Body Composition of Largemouth Bass zyxw Micropterus sulmoides zy LEIGH ANNE BRIGHT, SHAWN D. COYLE, AND JAMES H. TIDWELL Kentucky State University, Aquaculture Research Center, 103 Athletic Drive, Frankfort, Kentucky, 40601, USA Abstract-A feeding trial was conducted in aquaria with juvenile largemouth bass Micropterus salmoides to examine the effects of increasing dietary lipid levels on growth and body composition. Feed-trained largemouth bass fingerlings were graded to a similar size (16.3 f 2.4 g) and randomly stocked into 15 113.6- L glass aquaria at 25 fishlaquarium. Fingerlings were fed twice daily to apparent satiation with one of five isonitrogenous extruded experimental diets based on practical ingredients. Diets contained approximately 40% crude protein and either 0,5, 10, 15, or 20% added lipid. Due to background lipids in the ingredients, this equated to total lipid levels of 7, 10, 16, 20, and 23%, respectively. These diets had protein to energy ratios of 137, 120, 106.95, and 86 mgkcal. respectively. There were three replicate aquaria per dietary treatment. After 12 wk, there were no statistically significant differences (P zyxwvuts > 0.05) in average weight (g), specific growth rate zyxwv (8 body weightld), survival (%), or protein efficiency ratio (PER, %) among fish fed the five diets, which averaged79.3k5.6, 1.9k0.1,99.5*1.5,and2.11k 0.19, respectively. Juvenile largemouth bass fed diets containing 15 and 20% added lipid had significantly lower (P 50.05) feed conversion ratios (FCR) (1.1 k 0.0 and 1.1 k 0.1, respectively) than fish fed diets containing 0,5,and10%addedlipid(1.4kO0.1, 1.3kO.1,and 1.3 k 0.2, respectively). Proximate analysis of whole body samples indicated a significantly higher (P 10.05) lipid content in fish fed 15 and 20% added lipid compared to fish fed lower lipid levels. While FCR was lowest in fish fed the 15 and 20% added lipid diets, increased whole body lipid deposition may indicate that these levels are above optimal levels for juvenile largemouth bass. It appears that 7-16% total dietary lipid (PE:137-106 mgkcal) is sufficient to support efficient growth without impacting body composition in juvenile largemouth bass when fed a diet containing 40% crude protein. Largemouthbass Micropterus sulmoides (LMB) are recognized as one of the most commercially important freshwater sport fish in North America (Coyle et al. 2000). Traditionally, production of smalljuveniles for stock enhancement has been the focus of LMB production. Due to newly-emerg- ing markets for larger fish (> 1 kg), such as for corrective pond stocking and as a live food fish in ethnic Asian markets, demand has increased in recent years. This demand has been identified to be in excess of 318,000 kg/yr at > $6.60 per kg (Tidwell et al. 2000). Generally, feed costs constitute one of the largest components of production costs for most aquaculture operations, and protein is the most expensive dietary component in commercial feeds. Diets for carnivorous species such as largemouth bass usually contain not only high levels of crude protein (>a% of diet); but also contain high levels of expensive fish meal (> 25% of diet). In some species, dietary protein levels can be decreased by increasing non-protein energy sources. By supply- ing sufficient non-protein energy, the catabolism of protein for energy is minimized (Love11 1989). This is generally referred to as protein sparing. Although, dietary lipid can be used as a non-pro- tein energy source, excessive dietary lipid levels can have a negative impact on body composition (Nematipour et al. 1992; Tidwell et al. 1996). Therefore, evaluating the effects of increasing non-protein energy through the supplementation of lipids is important. Research has been conducted on protein with regards to dietary requirements (Anderson et al. 198 1 ; Tidwell et al. 1996). essential amino acid and highly unsaturated fatty acids (HUFAs) (Coyle et al. 2000), as well as carbohydrate tolerance (Good- win et al. 2000) of largemouth bass. However, the influence of varying dietary lipid and subsequent changes in the proteidenergy ratios has not yet been evaluated. Coyle et al. (2000) suggested 8 Copyright by the World Aquaculture Society zyxwv 2005 129