ASSESSMENT OF PULSED FEEDING STRATEGIES ON THE GUT METAGENOME OF TILAPIA IN POND CULTURE

Global production of farmed Nile tilapia (Oreochromis niloticus) has increased exponentially over the past 30 years. Feed comprises 50-70% of production costs for tilapia.  Here we assessed if reduced feeding might improve feed efficiency of tilapia in ponds in Bangladesh by utilizing pulsed feeding strategies along with fertilization [fed daily (Tx1), fed alternate days (Tx2), fed every third day (Tx3), not fed (Tx4)] and without fertilization [fed daily (Tx5)]. Tx1, Tx2, and Tx5 had the greatest growth and survival, while Tx2 had the best feed efficiency and overall benefit:cost ratio of all groups. Metagenomic studies were designed to establish gut microbial diversity changes due to these pulsed feeding strategies. We obtained about 20,000,000 total reads aligning to 225 16S (prokaryotic) operational taxonomic units (OTUs) and 288 18S (eukaryotic) OTUs. Metagenomic analyses indicated that Tx1 and Tx2 had the greatest diversity of bacteria and eukaryotes in the tilapia fecal material. Tx2 also had the highest observed eukaryotic counts. The predominant bacteria found were Cetobacterium somerae (a common gut colonizer of Nile tilapia), bacteria of family Peptostreptococcaceae, Clostridium perfringens, other bacteria of family Clostridiaceae, and cyanobacteria of order Euglenozoa (Figure 1); 20 unique species were found in Tx2 including the antibiotic producing Actinoplanes sp., the methanol utilizing Methylobacterium hispanicum, and the biodegrative Sphingomonas sp. The predominant eukaryotes were the diatoms of class Mediophyceae, phylum Rotifera, green algae of class Chlorophyceae, and the angiosperms of class Magnoliophyta; 15 unique species were identified in Tx2 including the green algae Chloromonas sp. These results indicate that feeding tilapia on alternate days in fertilized ponds provides significant cost savings to Bangladesh farmers with little impact on fish growth which supports previous studies in the Philippines. Additionally our results suggest that combined feeding and fertilization increases the diversity of microbiota available to the fish which may contribute to the improved efficiency of tilapia growout.