Efficacy of Utilization of All-Plant-Based and Commercial Low-Fishmeal Feeds in Two Divergently Selected Strains of Rainbow Trout (Oncorhynchus mykiss): Focus on Growth Performance, Whole-Body Proximate Composition, and Intestinal Microbiome

Abstract

The present study aimed to investigate the growth performance, whole-body proximate composition, and intestinal microbiome of rainbow trout strains when selected and non-selected for weight gain on all-plant protein diets. A 2x2 factorial design was applied, where a selected (United States) and a non-selected (ITA) rainbow trout strain were fed using either an all-plant protein (PP) or a commercial low-FM diet (C). Diets were fed to five replicates of 20 (PP) or 25 (C) fish for 105 days. At the end of the trial, growth parameters were assessed, and whole fish (15 pools of three fish/diet) and gut samples (six fish/diet) were collected for whole-body proximate composition and gut microbiome analyses, respectively. Independent of the administered diet, the United States strain showed higher survival, final body weight, weight gain, and specific growth rate when compared to the ITA fish (p < 0.001). Furthermore, decreased whole-body ether extract content was identified in the PP-fed United States rainbow trout when compared to the ITA strain fed the same diet (p < 0.001). Gut microbiome analysis revealed the Cetobacterium probiotic-like genus as clearly associated with the United States rainbow trout, along with the up-regulation of the pathway involved in starch and sucrose metabolism. In summary, the overall improvement in growth performance and, to a lesser extent, whole-body proximate composition observed in the selected rainbow trout strain was accompanied by specific, positive modulation of the intestinal microbiome.

Effects of plant-based proteins and handling stress on intestinal mucus microbiota in rainbow trout

“…As an exclusive representative of the phylum Fusobacteriota , we identified bacteria from the genus Cetobacterium, which is a common microbe in the intestine of fish like common carp 84 , bass 85 , and Nile tilapia 86 and was identified as a dominant representative in carnivorous teleostei 53 , 85 . In rainbow trout, however, Cetobacterium prevalence was reported frequently 39 , 41 , 63 , 64 , 67 , but not to the extent seen in the present study. Here, Cetobacterium abundance is high in trout line A and less abundant in trout line B.…”

“…Furthermore, differences explained by the factor diet are within the abundance of bacteria from the genus Mycoplasma, which is more abundant in fish fed with plant-based proteins in trout line A and less pronounced in trout line B. As the most dominant genus in the phylum Firmicutes , Mycoplasma represented 52% (mean) of the bacteria in trout line A and 76% (mean) in trout line B. Mycoplasma has been identified as a key member of the healthy gut microbiota in the intestinal digesta 52 , 59 , 62 – 66 and mucus 39 , 41 , 67 of rainbow trout and Atlantic salmon 45 , 68 – 72 using 16S rRNA amplicon sequencing. Huyben and colleagues 42 revealed a similar high abundance of Mycoplasma in both the intestinal digesta and mucosa when reared under different temperatures, and a comparable high abundance was also found in the intestinal contents of two susceptible breeding lines of rainbow trout reared under different stocking densities 62 .…”

Experimental evolution of a mammalian holobiont: selection for herbivorous capability in bank voles yields distinct and robust gut microbial communities

“…The differences between the microbiomes were mostly maintained, which suggest stability of the microbial alteration, but a bene cial role of that difference in the selected trait was not considered. In two experiments on sh selected for mass gain, sh from the selected and control lines hosted different microbiomes regardless of diet (Biasato et al 2022; Torrecillas et al 2023), but microbial exchange was not allowed. Thus, to our knowledge no previous selection experiment has simultaneously documented the stability of differentiated gut microbiomes with respect to dietary variation and microbial exchange, and the bene cial role of the microbial differences with respect to the selected trait.…”