Mannanoligosaccharides as a Carbon Source in Biofloc Boost Dietary Plant Protein and Water Quality, Growth, Immunity and Aeromonas hydrophila Resistance in Nile Tilapia (Oreochromis niloticus).

Asmaa T.Y Kishawy,Doaa Ibrahim,Nihal El Nahhas,Mohamed A Kamel,Taghrid M.N Abdelhakim,Abd Elhakeem I El-Murr,Shefaa A.M El-Mandrawy,Hend S Nada,Wael N Hozzein,Alaa H Sewid

doi:10.3390/ani10101724

Abstract

The aim of the present study was to evaluate mannan oligosaccharides (MOS) or glycerol (GLY) as a carbon source on biofloc systems of Nile tilapia (O. niloticus) juveniles. Fish (n = 750) were reared in open flow (Controls) or biofloc systems (B-GLY and B-MOS) fed with a plant or fish protein source over a period of twelve weeks. Total ammonia nitrogen and nitrate decreased in the biofloc groups, while biofloc volume increased in B-MOS. Compared to the controls, B-MOS and B-GLY exhibited higher weight gain and improved feed conversion, irrespectively of the diet. Serum level of C-reactive protein was reduced, while IgM and lysozyme activity was higher in the B-MOS fish, compared to other groups. Intestinal Bacillus spp. count was increased, whereas Vibrio, Aeromonas and Pseudomonas spp. counts decreased in B-MOS reared groups, compared to the other groups. The proinflammatory cytokine (IL-8 and IFN-γ) transcript expression was upregulated in B-MOS more than B-GLY reared groups. Compared to the controls, the virulence of Aeromonas hydrophila was decreased in the B-MOS and B-GLY groups. The results indicate several benefits of using MOS as a carbon source in a biofloc Nile tilapia system; a cost benefit analysis is required to assess the economic viability of this.

Highlights

The pollution of culture water in the semi-intensive and intensive systems for fish culture is due to the accumulation of fish waste and uneaten feed, as about 26% nitrogen and 30% phosphorus from feed are utilized by fish, the remainder causing an increase in bond nitrogen and ammonia load [1].Continuous and partial water exchange is necessary, especially in intensive fish culture, to maintain good water quality, which may cost about 10% of total production cost [2]
The growth performance parameters (final body weight (BW) and weight gain (WG), feed conversion ratio (FCR), protein efficiency ratio (PER) and specific growth rate) of Nile tilapia reared in biofloc systems were significantly (p < 0.05) improved against those reared in normal conditions as the control (Table 4)
PER of Nile tilapia reared in all biofloc groups recorded significantly (p < 0.05) higher PER than the control groups, while dietary protein sources had no significant effect on PER among experimental groups

Summary

Introduction

Continuous and partial water exchange is necessary, especially in intensive fish culture, to maintain good water quality, which may cost about 10% of total production cost [2]. Biofloc technology (BFT) is a recent technique developed to maintain water quality through up-taking water nitrogen and converting it to microbial protein [3]. Bioflocs comprise a mixture of heterogeneous floc-former microorganisms such as bacteria, microalgae, protozoa, phytoplankton, rotifers, annelids, nematodes, copepods, cations, colloids, organic polymers, uneaten feed and dead cells [4]. All floc formers aggregate with each other, forming a mass that fish can feed on and supporting nutrient recycling and improving fish growth performance [5,6]. The protein in the commercial fish diet can be decreased from 35% to 24%

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