Expanding Non-invasive Approaches for Fish-Health Monitoring: A Survey of the Epidermal Mucus Metabolomes of Phylogenetically Diverse Freshwater Fish Species.

There is a pressing need for more-holistic approaches to fisheries assessments along with growing demand to reduce the health impacts of sample collections. Metabolomic tools enable the use of sample matrices that can be collected with minimal impact on the organism (e.g., blood, urine, mucus) and provide high throughput, untargeted biochemical information without the requirement of a sequenced genome. These qualities make metabolomics ideal for monitoring a wide range of fish species, particularly those under protected status. In the current study, we surveyed the relative abundances of 120 endogenous metabolites in epidermal mucus across eight freshwater fish species belonging to seven phylogenetic orders. Principal components analysis was used to provide an overview of the dataset, revealing strong inter-species relationships in the epidermal mucus metabolome. Normalized relative abundances of individual endogenous metabolites were then used to identify commonalities across multiple species, as well as those metabolites that showed notable species specificity. For example, taurine was measured in high relative abundance in the epidermal mucus of common carp (Cyprinus carpio), northern pike (Esox lucius), golden shiner (Notemigonus crysoleucas), rainbow trout (Oncorhynchus mykiss), and rainbow smelt (Osmerus mordax), whereas γ-amino butyric acid (GABA) displayed a uniquely high relative abundance in flathead catfish (Pylodictis olivaris). Finally, hierarchical cluster analysis was used to evaluate species relatedness as characterized by both the epidermal mucus metabolome (phenotype) and genetic phylogeny (genotype). This comparison revealed species for which relatedness in the epidermal mucus metabolome composition closely aligns with phylogenetic relatedness (e.g., N. crysoleucas and C. carpio), as well as species for which these two measures are not well aligned (e.g., P. olivaris and P. spathula). These, and other findings reported here, highlight novel areas for future research with fish including development of epidermal mucus-based markers for non-invasive species-specific and -non-specific health monitoring, sex determination, and hypoxia tolerance. This article is protected by copyright. All rights reserved.