Dietary nucleotides: a novel supplement in fish feeds 1. Effects on resistance to disease in salmonids

To determine the effects of the inclusion of exogenous nucleotides in aquaculture diets on the resistance of fish to various challenge infections, trials were carried out and results presented. When added to normal fish feed formulations at a combined inclusion level of 0.03%, these additional nucleotides were shown to increase resistance to challenge infections with bacterial. viral and rickettsial diseases as well as ectoparasitic infestation. When fed for 3 weeks prior to challenge, the nucleotide-supplemented diet was superior (31% mortalities: relative percent survival: RPS = 37%) to a beta -glucan-containing diet (43% mortalities; RPS = 12%) in reducing mortalities due to Vibrio anguillarum infection in fish fed the control diet (49% mortalities). Mortalities resulting from infections with infectious salmon anaemia (ISA) virus and Piscirickettsia salmonis were also significantly reduced (RPS = 25.7% and 42.1%, respectively) as were the numbers of infesting sea lice (Lepeophtheirus salmonis) (37.8% reduction in the mean number of attached lice per fish). The mode of action of supplemental dietary nucleotides and advantages over recognised immunostimulants are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.