EFFECTS OF DIETARY PROBIOTICS ON THE GROWTH AND IMMUNITY OF TOR TAMBROIDES : A MOLECULAR APPROACH WITH EMPHASIS ON GENE EXPRESSION PROFILESLi Lian Wong*, Nguyen Thi Mai, Nursyafiqah Zahidah Azahar, Zulaikha Mat Deris and Norazimah YusofSchool of Fisheries and Aquaculture Sciences, Universiti Malaysia TerengganuEmail: lilian@umt.edu.my

Malaysian mahseer (Tor tambroides) has significant aesthetic and economic value as food and ornamental fish. The natural population of T. tambroides is currently suffering a dramatic decline in population size due to over-exploitation and environmental degradation. Due to the reduced population size and high market demand, artificial breeding program of this species have been developed for both conservation and aquaculture purposes. However, the growth rate of T. tambroides is highly reduced in captive breeding condition, and could only be improved by administration of expensive high protein diet. To reduce the total cost of aquaculture production, beneficial dietary supplements such as probiotics could be used as promising alternatives for viable farming of this species. Probiotics have been included in fish diet for numerous benefits which include enhancing the growth and improving disease resistance of the cultured species. In this study, we set out to determine whether addition of commercial probiotics (Bacillus subtilis) in the 30-day diet would improve the growth rate and immunity levels of T. tambroides. Measures of body weight and standard length were performed to assess juveniles growth. The immunity level and growth rate were observed through comparison of molecular responses following probiotics administration in control diet and probiotic supplemented diet. Insulin-like growth factor (Igf) gene was chosen as growth marker, while Heat-shock protein 70 (Hsp70) and Glutathione peroxidase (GPX) were selected as immune-related markers. We observed significant increase in the body weight of juvenile fish treated with probiotic supplemented diet, and the growth rate improvement was further proved by a significant 1.2 fold increase in the Igf gene expression level. However, there was no significant difference in the expression levels for both Hsp70 and GPX genes between control and probiotic treated groups. This data was resulted from the absence of challenge test with external stressors such as pathogenic infection, poor water quality and extreme temperature to induce the immunity genes expression. Overall, this preliminary study suggests a potent effect on the growth of juvenile T. tambroides, which provides primary insight into molecular entry path to investigate probiotic mechanisms responsible for growth enhancement of this species. With appropriate stress inducers incorporated into the experimental challenge test in our next study, we anticipate to prove the efficiency of dietary probiotics in regulating immune-related genes in T. tambroides.