Dietary arginine requirement of juvenile red sea bream Pagrus major Samad Rahimnejad, Kyeong-Jun Lee ⁎ Department of Marine Life Sciences, Jeju National University, Jeju 690-756, South Korea abstract article info Article history: Received 26 May 2014 Received in revised form 28 August 2014 Accepted 3 September 2014 Available online 11 September 2014 Keywords: Red sea bream Arginine requirement Growth performance Protein retention Hematology Innate immunity A 9-week feeding trial was carried out to evaluate dietary arginine requirement of juvenile red sea bream. Six isonitrogenous and isocaloric diets (50% crude protein and 17.7 kJ g -1 gross energy) were formulated to contain graded levels of arginine including 1.42, 1.88, 2.22, 2.54, 3.08 and 3.43% of diet (2.84–6.86% of dietary protein), and fed triplicate groups of fish (13.3 ± 0.2 g) to apparent satiation twice daily. At the end of the feeding trial, fish fed ≥2.22% arginine showed significantly (P b 0.05) higher growth than those fed 1.42% arginine. Significant improvement in protein productive value was found at dietary arginine level of 2.54% compared to the fish fed 1.42% arginine. Significant reductions in whole-body and muscle lipid contents were found by increment of arginine level and whole-body protein increased significantly in fish fed 2.22–2.54% arginine compared to those fed 1.42% arginine. Plasma total protein level significantly was increased in fish fed 2.54–3.08% arginine, and alanine aminotransferase activity and glucose level were significantly decreased in fish fed 2.22–2.54% and ≥1.88% arginine, respectively, compared to the group fed 1.42% arginine. Significant improvements in lyso- zyme and myeloperoxidase activities and total immunoglobulin level were obtained by dietary arginine incre- ment. Also, significantly higher total nitric oxide synthase activity was recorded at 3.08% arginine level in comparison to 1.42% arginine. A broken-line regression analysis on weight gain showed that the optimum dietary arginine level is 2.37% of diet (4.74% of dietary protein). © 2014 Elsevier B.V. All rights reserved. 1. Introduction Quantitative estimation of the essential amino acid (EAA) require- ments in diets for fishes is extremely important due to their critical impacts on muscle deposition, feed costs and nitrogen wastes (Nguyen and Davis, 2009; Small and Soares, 1999). Dietary amino acid balance, especially the balance of EAA is the main factor affecting protein availability. Fish cannot synthesize all amino acids, and appropriate amount of EAA needs to be supplied in the diet to meet the requirements (NRC, 2011). Deficiency of dietary EAA leads to im- paired protein synthesis, reduced growth performance and poor feed utilization (Cowey, 1979; Wilson and Halver, 1986). On the other hand, excessive levels of EAA will result in increased ammonia excretion (Cai et al., 1996; Yang et al., 2002). Arginine has been established as an EAA in diets of many fish species (Cowey, 1994; NRC, 1993). It is the most limiting amino acid in plant protein sources such as corn, sesame and zein meal (Berge et al., 1997; Luo et al., 2007; Mai et al., 1994). Arginine has been documented to participate in several essential growth-related processes, including an insulinotropic effect (Hird, 1986; Plisetskaya et al., 1991). It is a precursor of several biologically im- portant metabolites including nitric oxide (NO), polyamines and creatine (Galli, 2007; Grillo and Colombatto, 2007; Wu and Morris, 1998). Also, it participates in several metabolic pathways including protein synthesis, urea production and metabolism of glutamic acid, proline, glucose and fatty acids (Flynn et al., 2002; Hird, 1986). Arginine has been established as an immunonutrient in higher animals such as humans, rodents, swine and poultry (Evoy et al., 1998; Li et al., 2007; Roth, 2007; Wu, 2010). There have been accumulating evidences that arginine influences immune function in fish as well (Buentello and Gatlin, 1999, 2001; Buentello et al., 2007; Cheng et al., 2011). According- ly, the changes in immune response of fish are taken into account in ar- ginine requirement studies (H. Zhou et al., 2012; Pohlenz et al., 2014; Q.C. Zhou et al., 2012; Ren et al., 2013; Ren et al., 2014; Yue et al., 2013). The dietary arginine requirement has been estimated for many fish species and literature review shows the high variations in requirement level among species. Therefore, it is critical to determine the quantita- tive arginine requirement for each species. Red sea bream is one of the most important fish in Korea and Japan. Total amount of 2755 tons red sea bream was produced in Korea in 2013 (Ministry of Maritime Affairs and Fisheries of Korea, 2013). However, to the best of our knowl- edge, quantitative requirements of the species for EAAs have just been reported for lysine (Forster and Ogata, 1998) and valine (Rahimnejad and Lee, 2013) and there is no available data on its arginine require- ment. Therefore, the present study was carried out to evaluate the dietary arginine requirement of red sea bream based on growth Aquaculture 434 (2014) 418–424 ⁎ Corresponding author. Tel.: +82 64 754 3423; fax: +82 64 756 3493. E-mail address: kjlee@jejunu.ac.kr (K.-J. Lee). http://dx.doi.org/10.1016/j.aquaculture.2014.09.003 0044-8486/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online