EFFECT OF PULSED FEEDING ON GROWTH, GUT METAGENOME, AND INTESTINAL NUTRIENT TRANSPORTERS 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 grown in ponds in Bangladesh by utilizing pulsed feeding strategies along with weekly pond 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 million total reads aligning to 225 16S (prokaryotic) operational taxonomic units (OTUs, e.g. different genus/species) 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 (Figure 1). The predominant bacteria found were Cetobacterium somerae (common gut colonizers of Nile tilapia), bacteria of family Peptostreptococcaceae, and Clostridium perfringens. 20 unique species were found in Tx2 including an antibiotic producing Actinoplanes sp., the methanol utilizing Methylobacterium hispanicum, and the biodegrative Sphingomonas sp. The predominant eukaryotes in the tilapia fecal material were the diatoms of class Mediophyceae, phylum Rotifera, green algae of class Chlorophyceae, and the angiosperms of class Magnoliophyta. Gene expression of solute transporters found in the proximal intestine was investigated. Transporter gene expression in the Tx2 regime tended to be higher than feeding alone, but lower than the other feeding + fertilization and fertilization alone regimes. This intermediate expression of transporters with alternate day feeding may reflect a condition for most efficient uptake of nutrients from the GI tract of tilapia.  Overall, the results indicate that feeding tilapia on alternate days in fertilized ponds can provide significant cost savings to Bangladesh tilapia farmers with little impact on fish growth, which supports previous studies in the Philippines. Additionally our results suggest that combined alternate-day feeding and fertilization increases the diversity of microbiota available to the fish and regulates nutrient uptake, which may contribute to the improved efficiency of tilapia growout.