DOSE-DEPENDENT RESPONSE OF NILE TILAPIA, OREOCHROMIS NILOTICUS (LINNAEUS 1757) AND AFRICAN CATFISH, CLARIAS GARIEPINUS (BURCHELL 1822) TO FUMARIC OR BUTYRIC ACIDS

Abstract

Dietary additives especially antibiotics used in fish diets have been found to have adverse effects on fish, consumers and the environment. Organic acids have been sought as substitutes for antibiotics, hence, the focus of this work was to assess the effect of fumaric or butyric acids on performance of Oreochromis niloticus and Clarias gariepinus. Thestudy was carried out atThe Teaching and Research Farm of the Department of Fisheries and Aquaculture Technology, the Federal University of Technology, Akure, Nigeria. The experiment was carried out in two phases, using fumaric acid in the first phase and butyric acid in the second phase. In fumaric acid supplemented phase, 30 and 40 % crude protein diets were used to feed O. niloticus and C. gariepinus respectively, while in the butyric acid phase, 35 and 40 % were used. Diets were designated based on fish species and organic acids, while diets without organic acids served as controls. Fumaric or butyric acids were added to the basal ingredients at 0, 0.5, 1.0, 1.5 and 2.0 % inclusion levels. Fish were stockedat 15 per tank with each treatment in triplicate. The mean stocking weights of O. niloticus and C. gariepinus in the first phase were 8.36±0.13 g and 6.73±0.65 g and in the second phase 14.43±0.21 g and23.32±0.62 g respectively. Fish were acclimated to experimental conditions for seven days and fed with the respective control diets.Fish were fed in two equal portions daily at 08:00 – 09:00 and 16:00 – 17:00 GMT for 84 days. Fish in each experimental unit were batch-weighed fortnightly and some water parameters monitored.Temperature, dissolved oxygen and pH were determinedusing a combined digital YSI Meter andportable pH meter. Water quality parameters measured were within the recommended range for the culture of tropical fishes.Blood samples were analyzed using standard methods. Histological examinations of liver, kidneys and intestines were carried out using appropriate laboratory procedures. A challenge test was conducted on five fish samples in each replicate using Aeromonas sobriafor 14 days.All data were subjected to one-way ANOVA using Statistical Package for Social Science (SPSS), version 19.0. Significant means were separated using Duncan’s Multiple Range Ad-hoc Test at p>0.05. Results of this study showed significant differences(p<0.05) in most of the parameters measured. O. niloticus and C. gariepinus fed diets ONFA2 and CGFA3 had the highest weight gain (WG), specific growth rate (SGR), feed intake (FI) and survival and the best feed conversion ratios (FCR). In the butyric acid supplemented diets the highest WG, SGR, FI and best FCR were recorded in O. niloticus and C. gariepinus fed diets ONBA4 and CGBA5 respectively.Significant differences (p<0.05) were recorded in O. niloticus fed fumaric acid supplemented diets while survival in C. gariepinus were not significantly different(p>0.05). O. niloticus and C. gariepinus fed fumaric acid supplemented diets ONFA3 and CGFA3 had more protein retained in the body while and the least were recorded in fish fed butyric acid supplemented diets ONBA1 and CGBA2. O. niloticus and C. gariepinus fed fumaric acid diets ONFA5 and CGFA2 had the highest haemoglobin (Hb), packed cell volume (PCV), red blood cells (RBCs) and mean cell haemoglobin concentration (MCHC). In the butyric acid phase, C. gariepinus fed diet CGBA1 (control) had the highest Hb, PCV, RBC and MCHC. O. niloticus fed diets ONBA4 had the highest Hb and PCV while the control (ONBA1) recorded the highest WBCs and RBCs. In the challenge test, 100 % survival was recorded in fish fed ONFA5, ONBA4 and CGFA4 while the lowest wererecorded fish fed control diets.Normal hepatocytes, renal tubules and columnar epitheliumstructures were observedin the liver, kidney and intestines in both phases.Hepatocyte vacuolation in and reduction in muscularis mucosa and desquamation of villi and micro-villi were observed in both fish species.Reduction in muscularis thickness of small intestines has been found to be helpful in digestion and absorption of nutrients.Due to the positive results obtained in this study, dietary organic acids may be used as growth promoters in the feeds of C. gariepinus and O. niloticus at 0.5 – 1.0 % for fumaric acid and 1.5 – 2.0 % for butyric acid for growth and prophylaxis.