Abstract

Basal diet containing 0.5, 1.0, 1.5 and 2.0 g kg^-1 mixture of inosine monophosphate (IMP), adenosine monophosphate (AMP), guanosine monophosphate (GMP), uridine monophosphate (UMP) and cytidine monophosphate (CMP) (1:1:1:1:1) (mixed-NT; Experiment 1) and 1.5 g kg^-1 from each nucleotides and mixed-nucleotides (NT; Experiment 2) were fed to triplicate groups of grouper for 8 weeks. Basal diet without NT was used as control in both Experiments. In Experiment 1, fish fed the diet with 1.5 g mixed-NT kg^-1 had higher (P < 0.05) weight gain (WG) than the control group. The superoxide anion (O₂^-) production ratio was higher in fish fed diets with 1.0-1.5 g mixed-NT kg^-1 than the fish fed diets with £0.5 g mixed-NT kg^-1. In Experiment 2, fish fed diets with nucleotides had higher WG than the control group. The O₂^- production ratio was higher in fish fed the diet with 1.5 g AMP kg^-1, followed by fish fed diets with 1.5 g UMP and mixed-NT kg^-1, and lowest in the control group. These results suggest that growth and immune responses were enhanced in grouper fed diet with 1.5 g mixed-NT kg^-1 diet. Diet with 1.5 g kg^-1 of AMP seems to be more beneficial on the immune responses in fish than other nucleotides.

key words: grouper, growth, immune responses, nucleotides

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Received 13 September 2007, accepted 6 December 2007

Correspondence: Shi-Yen Shiau, Department of Food and Nutrition, Providence University, 200 Chung-Chi Road, Shalu, Taichung County 433, Taiwan. E-mail: syshiau@pu.edu.tw

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Introduction

Nucleotides (NT) have essential physiological and biochemical functions including encoding and deciphering genetic information, mediating energy metabolism and cell signaling as well as serving as components of coenzymes, allosteric effectors and cellular agonists in terrestrial animals (Carver & Walker 1995).

In fish, early research has been focused on diet palatability (Mackie 1973) and feeding behavior (Kiyohara et al. 1975; Ishida & Hidaka 1987) for supplementation of NT in fish diets. Burrells et al. (2001a) reported that dietary NT supplementation improved Atlantic salmon growth. Dietary NT supplementation has been reported to enhance immune responses and disease resistance of tilapia (Ramadan et al. 1994), Atlantic salmon (Burrells et al. 2001b) and hybrid striped bass (Li et al. 2004). It should be noted, however, that commercial NT product was used in the above studies. Besides NT, the commercial product contains RNA and impure components, such as trace mineral and polysaccharides as well. Recently, supplementation of purified NT mixture in diet has been demonstrated to enhance the growth of red drum (Li et al. 2007a) and white shrimp (Li et al. 2007b). Red drum fed diet with NT mixture did not alter immune response and disease resistance (Li et al. 2007a). The actual role of NT on growth and immune responses in fish needs to be clarified.

Grouper are high-quality seafood in Asia and around the world. They are also good candidates for intensive aquacul-ture because of their desirable taste, hardiness in a crowded environment and rapid growth. The purpose of the study was to elucidate the effects of either supplementation with the mixture of five NT, i.e., inosine monophosphate (IMP), adenosine monophosphate (AMP), guanosine monophosphate (GMP), uridine monophosphate (UMP) and cytidine monophosphate (CMP) or with each of the individual NT on the growth of grouper, Epinephelus malabaricus. Head kidney leucocyte superoxide anion production ratio and plasma total immunoglobulin concentration in fish were also monitored as indicators of the non-specific immune responses in fish.