_____________________________________________________ * Corresponding author. E-mail address: karen_perhaps12@yahoo.com Asian Fisheries Science 25 (2012):180-192 Asian Fisheries Society ISSN 0116-6514 Effects of Dietary Nucleotides on the Immune Response and Growth of Juvenile Pacific White Shrimp Litopenaeus vannamei (Boone, 1931) KAREN GRACE S. ANDRINO * , AUGUSTO E. SERRANO JR. and VALERIANO L. CORRE JR. Institute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, 5023 Miag-ao, Iloilo, Philippines. Abstract Effects of dietary supplementation of nucleotides on immune response, survival against white spot syndrome virus (WSSV) challenge infection and growth of Pacific white shrimp Litopenaeus vannamei (Boone, 1931) juveniles were evaluated. The basal diet for Pacific white shrimp supplemented with nucleotide formula (Vannagen; Chemoforma, Augst, Switzerland) at 0%, 0.2%, 0.4% and 0.6% kg -1 of feed were tested. Survival of shrimp was in the range of 92-97% and was not significantly different among treatments. However, specific growth rate (SGR), feed conversion efficiency (FCE) and protein productive value (PPV) were significantly better in shrimps fed the nucleotide-supplemented diet than those fed the control diet after a 60-day feeding trial. Survival of test animals upon challenge with WSSV infection was significantly higher in the nucleotide group than in the control group. Immune response indices i.e. total haemocyte count (THC), respiratory burst activity and phenoloxidase activity were significantly enhanced in shrimp fed diets containing nucleotides as compared to those fed diets with no supplementation. At the levels tested, 0.2% nucleotide in the diet was the optimum. These results indicate that dietary supplementation of nucleotides resulted in beneficial effects in improving growth, feed utilisation, protein utilisation and accelerate shrimp immune response against WSSV infection. Introduction Aquaculture continues to be the fastest growing animal food-producing sector and is making an important contribution to shellfish production which is a high value activity worldwide. Shrimp farming for instance constitutes an important source of revenue and employment in many developing countries. However, infectious diseases have affected the profitability of the shrimp industry (Rodriguez and Le Moullac, 2000). The white spot syndrome virus (WSSV), one of the most devastating viral pathogen, has already become established in the local marine environment and in wild populations of shrimps in the Philippines (de la Peña et al. 2007). This virus has emerged as the most serious threat to commercial shrimp farming. Traditional control strategies for the disease are being employed such as the use of antibiotics and chemical disinfectants. These are no longer recommended due to the emergence of pathogen-resistance and to the growing concerns over environmental impact and wildlife protection (Rocha-Montero et al. 2006). In keeping with developments in aquaculture, shrimp immunology has become a key element in establishing strategies for the