Relative use of dietary carbohydrate, non-essential amino acids, and lipids for energy by hybrid striped bass, Morone chrysops ♀ × M. saxatilis ♂ Xiaoyi Wu a , Sergio Castillo b , Misael Rosales b , Alton Burns b , Maria Mendoza b , Delbert M. Gatlin III b, ⁎ a Department of Aquaculture, Hainan University, Haikou 570228, China b Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843-2258, USA abstract article info Article history: Received 27 July 2014 Received in revised form 18 September 2014 Accepted 19 September 2014 Available online 26 September 2014 Keywords: Hybrid striped bass Carbohydrate Non-essential amino acids Lipid A comparative feeding trial was undertaken to evaluate the relative use of dietary carbohydrate, non-essential amino acids (NEAA), and lipids for energy by hybrid striped bass Morone chrysops ♀ × M. saxatilis ♂. The control diet was formulated to contain 40% crude protein, 25% dextrinized corn starch as available carbohydrate (CHO) and 10% lipid. In the three experimental diets, the 25% dextrinized starch was replaced with either, 25% NEAA (12.5% L-glutamate and 12.5% L-aspartate), an additional 11% lipid (21% total lipid; designated high-lipid diet), or 0% CHO with protein and lipid components concentrated to 53.3% and 13.3%, respectively, and each diet was fed to juvenile fish such that all groups received equal amounts of intact protein. Juvenile hybrid striped bass (average initial weight of 21.1 g/fish) were stocked as groups of 12 fish in 110-L aquaria containing fresh water and operated as a recirculating system. Fish in triplicate aquaria were fed each dietary treatment at a rate approaching apparent satiation for 6 weeks. Fish fed the control diet with 25% CHO or high-lipid diet had significantly (P b 0.05) higher weight gain (WG) than those fed the 25% NEAA or 0% CHO diets. Fish fed the 25% NEAA or 0% CHO diets had similar WG. Protein efficiency ratio (PER) of fish fed the 25% CHO control diet was significantly higher than fish fed the 25% NEAA diet but did not differ significantly from those of fish fed the high-lipid or 0% CHO diets. Fish fed the control and high-lipid diets had significantly higher protein productive value (PPV) than those fed the 25% NEAA or 0% CHO diets. Hepatosomatic index (HSI) and hepatic glycogen content of fish fed the 25% CHO control diet were significantly higher than that of fish fed all other diets while their liver protein and lipid contents were signifi- cantly lower than fish fed the other experimental diets. Fish fed the high-lipid diet displayed significantly higher intraperitoneal fat (IPF) ratio, whole-body lipid and muscle lipid compared to fish fed the other diets. Results of this study indicated that with diets containing 40% crude protein, and energy supplied by 25% dextrinized starch provided similar growth performance of hybrid striped bass and achieved less carcass lipid deposition compared to an equal supply of energy from lipid. Dietary NEAA (glutamate and aspartate) was converted to hepatic glycogen and carcass lipid, but did not have positive effects on growth performance of hybrid striped bass. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Non-essential amino acids (NEAAs) have received less attention in fish nutrition when compared to essential amino acids (EAAs). Published results evaluating NEAAs indicate that they are a better energy source than EAAs for fish and other animals based on observed effects such as improvement of growth of tilapia (Gaye-Siessegger et al., 2007; Mambrini and Kaushik, 1994) and rainbow trout (Green et al., 2002; Schuhmacher et al., 1995), protein sparing of alanine and glycine in diets of Atlantic salmon (Abboudi et al., 2009), as well as the firming of fillets and improving of Atlantic salmon health (Larsson et al., 2014). In Atlantic salmon (Larsson et al., 2014), glutamate supple- mentation altered energy metabolism by reducing fat accumulation in the liver, and in herring larvae (Conceição et al., 2002), it was reported that glutamate was used preferentially to lysine as an energy substrate. In the rat, alanine, glutamate, glutamine and aspartate are preferentially used as energy substrates, while the other NEAAs and the EAAs are spared for the synthesis of proteins, in particular when dietary protein is inadequate or when dietary AAs are unbalanced (Tanaka et al., 1995). In juvenile turbot (Cowey and Sargent, 1979) and rainbow trout (Kim et al., 1992), oxidation of NEAAs was found to be higher than the oxidation of EAAs. Up to date, utilization of NEAAs as energy sources in hybrid striped bass has not yet been investigated, and thus the first aim of this study was to evaluate the use of NEAAs (glutamate and aspartate) for energy Aquaculture 435 (2015) 116–119 ⁎ Corresponding author. Tel.: +1 979 847 9333; fax: +1 979 845 4096. E-mail address: d-gatlin@tamu.edu (D.M. Gatlin). http://dx.doi.org/10.1016/j.aquaculture.2014.09.030 0044-8486/© 2014 Elsevier B.V. All rights reserved. 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