EFFECTS OF A NEW PHYTOGENIC ON NILE TILAPIA GROWTH PERFORMANCE, GUT MICROBIOME AND DISEASE RESISTANCE AGAINST EMERGENT PATHOGEN Francisella noatunensis

Today, the main challenge faced by the aquaculture industry is to reduce antibiotics use during diseases occurrence. Among potential alternatives, phytogenic compounds are good candidates.  

In recent years, outbreaks caused by Francisella spp has gained notoriety as the major pathogen of tropical fish cultivated worldwide because of its emergence in several countries.

The current work evaluated the effects of continuous dietary supplementation of a new phytogenic on juvenile Nile tilapia (Oreochromis niloticus) growth performance, gut microbiome and resistance against the pathogen Francisella noatunensis.

The study has been conducted at State University of Londrina (Brazil). Apparent healthy Nile tilapia juveniles (O. niloticus) were obtained from a commercial hatchery from Paraná state, Brazil (initial weight 35g). Fishes were divided into 3 equal treated groups (140 individuals per treatment) stocked in 150 L tanks: a negative control (NC) not challenged by pathogen, a positive control (PC) and a tested group G1 supplemented with 0.2% phytogenic product (A-Live, MiXscience, France). Groups G1 and PC were challenged with Francisella noatunensis.

Due to its wide antimicrobial spectrum of action, the phytogenic must play a role on gut biodiversity and taxonomic abundance.

For this reason, intestinal microbiome of tilapia was analysed. Total DNA was extracted from entire intestinal fish tract and taxonomic classification was then realized.

Mortality and growth parameters correlated to the modification of gut microflora were finally measured.

Study of diversity suggested that in presence of Francisella spp., the treated group G1 had an increase of diversity in the gut bacterial microbiome when compared with NC and PC.

Higher diversity may limit implementation of pathogenic microorganisms. Study of abundance groups consolidated this hypothesis and indicated that in the treated group, frequency of opportunistic pathogens like Vibrionacae was lower suggesting a higher and better modulation from the phytogenic supplementation.

This reduction of pathogenic pressure positively impacted resistance of tilapia challenged by Francisella spp.  Survival was higher and performance of G1 fish were statistically restored compared with NC (Table 1).

By positively modulating gut microflora and by increasing biodiversity, phytogenics with wide spectrum of antimicrobial potential like A-Live contribute to leverage resistance of tilapia challenged by Francisella spp and associated opportunistic pathogens.