# The nasal microbiota of two marine fish species: diversity, community structure, variability, and first insights into the impacts of climate change-related stressors

## TL;DR

This study explores the nasal microbiota of two marine fish species, revealing distinct bacterial communities and how they respond to environmental factors and climate change stressors.

## Contribution

The first comprehensive analysis of nasal microbiota in marine fish and its response to climate change-related stressors.

## Key findings

- Seabass and cod nasal microbiota showed distinct bacterial profiles, with Stenotrophomonas and Ralstonia dominating, respectively.
- Seabass nasal microbiota showed higher alpha diversity and variability compared to cod.
- Climate change-related stressors did not significantly alter cod nasal microbiota structure.

## Abstract

Vertebrate nasal microbiota (NM) plays a key role regulating host olfaction, immunity, neuronal differentiation, and structuring the epithelium. However, little is known in fish. This study provides the first comprehensive analysis of the NM in two marine fish species, the European seabass and the Atlantic cod. Given its direct environmental exposure, fish NM is likely influenced by seawater fluctuations. We analysed the community structure, specificity regarding seawater, and interindividual variability of 32–38 fish reared under ambient conditions. Additionally, we conducted an experiment to investigate the influence of acidification and a simplified heatwave on cod NM (three fish per replicate). High-throughput 16S rRNA sequencing revealed species-specific NM communities at the genus-level with Stenotrophomonas and Ralstonia dominating seabass and cod NM, respectively. This suggests potential habitat- or physiology-related adaptations. The most abundant bacterial genera in seabass NM were also present in seawater, suggesting environmental acquisition. Alpha diversity was highest in Brest seabass NM and variability greatest in Tromsø cod NM. Simulated climate change-related scenarios did not significantly alter cod NM structure. We propose a minimum of 13 cod rosettes per replicate for future studies. This research establishes a foundation for understanding marine fish NM and its response to environmental changes.

Seabass and cod nasal microbiota showed distinct profiles from each other and from nonmarine fish, and varies with site in seabass but remains unaffected by climate change-related treatments in cod.