Effects of a Bioprocessed Soybean Meal Ingredient on the Intestinal Microbiota of Hybrid Striped Bass, Morone chrysops x M. saxatilis

The hybrid striped bass (Morone chrysops x M. saxatilis) is a carnivorous species and a major product of US aquaculture. To reduce costs and improve resource sustainability, traditional ingredients used in fish diets are becoming more broadly replaced by plant-based products; however, plant meals can be problematic for carnivorous fish. Bioprocessing has improved nutritional quality and allowed higher inclusions in fish diets, but these could potentially affect other systems such as the gut microbiome. In this context, the effects of bioprocessed soybean meal on the intestinal bacterial composition in hybrid striped bass were investigated. Using high-throughput sequencing of amplicons targeting the V1–V3 region of the 16S rRNA gene, no significant difference in bacterial composition was observed between fish fed a control diet, and fish fed a diet with the base bioprocessed soybean meal. The prominent Operational Taxonomic Unit (OTU) in these samples was predicted to be a novel species affiliated to Peptostreptococcaceae. In contrast, the intestinal bacterial communities of fish fed bioprocessed soybean meal that had been further modified after fermentation exhibited lower alpha diversity (p < 0.05), as well as distinct and more varied composition patterns, with OTUs predicted to be strains of Lactococcus lactis, Plesiomonas shigelloides, or Ralstonia pickettii being the most dominant. Together, these results suggest that compounds in bioprocessed soybean meal can affect intestinal bacterial communities in hybrid striped bass.

183 Effects of Protein Supplementation on the Gut Bacterial Community Composition of Hybrid Striped Bass, Morone Chrysops X M. Saxatilis

Plant-based protein ingredients have become an attractive substitute for traditional animal sources in the aquaculture feed industry. However, inclusion in carnivorous fish diets is limited due to reduced digestibility, presence of anti-nutritional factors, and increased risk of digestive tract inflammation. To gain further insight on the adaptation of the fish digestive tract environment to plant-based protein sources, intestinal bacterial communities from Hybrid Striped Bass, Morone chrysops x M. saxatilis, fed diets supplemented with different protein sources were compared. Data were generated by Illumina MiSeq 2X300 sequencing of PCR generated amplicons targeting the V1–V3 regions of the 16S rRNA gene. A comparative analysis using the non-parametric Kruskal-Wallis test identified 17 highly represented species-level Operational Taxonomic Units (OTUs) that differed in abundance across dietary treatments (P &lt; 0.05). Notably, OTU SD_McMs-0001 was at its highest abundance in samples from individuals fed poultry-fishmeal (PFM; 47.61% ± 0.92%) and plant protein-based (PP; 43.13% ± 1.76%) diets, while it was found in much lower abundance in the non-supplemented control diet samples (B; 4.29% ± 0.92%). It was predicted to be a novel species of the family Peptostreptococcaceae based on its limited 16S rRNA gene sequence identity to its closest valid relative (Peptostreptococcus russellii, 91%). In contrast, three Proteobacteria-affiliated OTUs (SD_McMs-0002, SD_McMs-0003, and SD_McMs-0004) were most highly represented in B diet samples, with averages of 30.28%, 27.22%, and 13.54%, respectively. They were in much lower abundance in the PFM and PP samples, with averages ranging between 0.18% and 4.82%, respectively. Based on 16S rRNA sequence comparisons, they were predicted to be strains of Plesiomonas shigelloides (99%), Ralstonia pickettii (99%) and Sphingomonas elodea (99%), respectively. These results indicate that protein supplementation affects gut bacterial community composition of Hybrid Striped Bass, but that the type of protein used has minimal or no detectable impact.

Synchronous changes in length at maturity across four species of Lake Erie fish with different harvest histories

Decreases in size at maturation in harvested fish populations can reduce productivity and resilience. Delineating the causes for these changes in maturation is challenging. We assessed harvest and large-scale ecosystem variability as causes for changes in maturation in four Lake Erie fishes. Regulated harvests of Yellow Perch (Perca flavescens) and Walleye (Sander vitreus) are greater than unregulated harvests of White Perch (Morone americana) and White Bass (Morone chrysops). Our assessment considered cohort data from 1991-2012 for each species. We used a conceptual model of harvest-induced plasticity to show that changes in female length at 50% maturity (L50) were unrelated to harvest intensity in all species. We then demonstrated that changes in female L50 among cohorts were synchronous across species. Post-hoc analysis of variables capturing year-to-year variation in climatic and lake conditions suggested L50 was larger when water levels were near the norm for the study period and smaller at low and high levels. We conclude that changes in L50 were most strongly related to ecosystem changes unrelated to harvest intensity.