A diverse microbiome may improve the adaptability of salmon at the sea stage

A recent study explored the intestinal microbiota of Atlantic salmon during the seawater transfer process and found that gradually exposing the fish to changes in salinity led to a greater diversity in their intestinal bacterial communities – which could be associated with greater resilience and improved health.

The Fish Site
by The Fish Site
13 January 2023, at 8:30am
salmon smolt swimming in a tank
Salmon post smolts

Researchers explored the intestinal microbiota of Atlantic salmon that were exposed to gradual changes in salinity during smoltification © Terje Aamodt, Nofima

There is wide consensus that the health and well-being of fish is highly influenced by their microbiota, which can play a fundamental role in different biological processes such as metabolism and immune response of the fish.

Therefore, it is important to understand how the microbiome of organisms is altered by environmental effects and host conditions and how this influences the health of the host. In this regard, the Aquaculture Genomics line (RP1) of the Interdisciplinary Centre for Aquaculture Research (INCAR) is carrying out a series of studies to understand the factors that shape the intestinal microbiota in fish to promote healthy organisms, favouring their well-being in aquaculture production.

Recently, the researchers of INCAR RP1, Dr (c) María F Morales-Rivera, Dr Diego Valenzuela-Miranda, Dr Gustavo Núñez-Acuña, Bárbara P Benavente, Dr Cristian Gallardo-Escárate and Dra Valentina Valenzuela-Muñoz, published “Atlantic salmon (Salmo salar) transfer to seawater by gradual salinity changes exhibited an increase in the intestinal microbial abundance and richness,” a study that delves into the bacterial communities associated with the process of transferring salmonids from freshwater to seawater. For this research, scientists designed an experiment where the intestinal microbiota of salmon transferred to seawater was evaluated under different strategies: saline shock, gradual change in salinity and use of a food with a special formulation to prepare a more robust fish when transferred to sea.

When asked, the researchers said that this was the first study to explore the intestinal microbiota of Atlantic salmon that were exposed to gradual changes in salinity during smoltification. “This study aimed to explore the diversity and abundance of intestinal microbiota in Atlantic salmon during transfer to seawater under three strategies. One group was exposed to gradual salinity change, a second group to salinity shock and the third was fed a functional diet prior to transfer to seawater. For this, researchers used Oxford Nanopore sequencing technology, letting them sequence the complete 16S gene. This allows researchers to identify individual species from samples. Additionally, the study describes the possible functionality of the microbial communities that are identified in each group of fish,” they said.

The findings revealed that the group exposed to salinity changes and the group fed with a functional diet present a greater microbial diversity, suggesting a positive relationship between bacterial communities and the health of fish transferred to seawater under both strategies. “The results obtained can be used as an additional tool to evaluate smolts prior to their transfer to seawater and would help in the well-being and survival of Atlantic salmon during the transfer stage to seawater,” the scientists highlight.

The study shows that carrying out the transfer of fish through gradual salinity changes leads to a greater richness in the bacterial communities of the fish, which could be associated with better health conditions and resilience. Within the bacterial communities, proteobacteria were dominant. However, the investigators observed variations in the lower taxonomic levels between the experimental groups.

salmon smolts swimming in a tank
Salmon smolts swimming in a tank

The study shows that carrying out the transfer of fish through gradual salinity changes leads to a greater richness in the bacterial communities of the fish, which could be associated with better health conditions and resilience © Salmon Evolution

Additionally, the INCAR Research team, due to the methodology used for the microbiota study, was able to identify the functional role of the bacterial groups identified in the different experimental groups. With these results, they noted that despite the taxonomic differences found between treatments, a small number of the identified metabolic pathways present significant differences between the groups evaluated. Most of them were related to biosynthesis processes.

Finally, this research shows that the implementation of gradual changes in salinity prior to transfer to seawater generates a greater richness in the intestinal microbiota for Atlantic salmon. This could lead to greater adaptability to seawater and reduce the mortality rate during this stage of the production process.