Abstract
BackgroundInfectious diseases cause significant production losses in aquaculture every year. Since the gut microbiota plays an essential role in regulating the host immune system, health and physiology, altered gut microbiota compositions are often associated with a diseased status. However, few studies have examined the association between disease severity and degree of gut dysbiosis, especially when the gut is not the site of the primary infection. Moreover, there is a lack of knowledge on whether bath treatment with formalin, a disinfectant commonly used in aquaculture to treat external infections, might affect the gut microbiome as a consequence of formalin ingestion. Here we investigate, through 16S rRNA gene metabarcoding, changes in the distal gut microbiota composition of a captive-reared cohort of 80 Atlantic salmon (Salmo salar L.), in consequence of an external bacterial skin infection due to a natural outbreak and subsequent formalin treatment.ResultsWe identified Tenacibaculum dicentrarchi as the causative disease pathogen and we show that the distal gut of diseased salmon presented a different composition from that of healthy individuals. A new, yet undescribed, Mycoplasma genus characterized the gut of healthy salmon, while in the sick fish we observed an increase in terms of relative abundance of Aliivibrio sp., a strain regarded as opportunistic. We also noticed a positive correlation between fish weight and Mycoplasma sp. relative abundance, potentially indicating a beneficial effect for its host. Moreover, we observed that the gut microbiota of fish treated with formalin was more similar to those of sick fish than healthy ones.ConclusionsWe conclude that external Tenacibaculum infections have the potential of indirectly affecting the host gut microbiota. As such, treatment optimization procedures should account for that. Formalin treatment is not an optimal solution from a holistic perspective, since we observe an altered gut microbiota in the treated fish. We suggest its coupling with a probiotic treatment aimed at re-establishing a healthy community. Lastly, we have observed a positive correlation of Mycoplasma sp. with salmon health and weight, therefore we encourage further investigations towards its potential utilization as a biomarker for monitoring health in salmon and potentially other farmed fish species.
Highlights
Infectious diseases cause significant production losses in aquaculture every year
Fish diseases are a cause of major production losses every year in the world of aquaculture [3] and many of them are caused by bacterial pathogenic infections (e.g. Vibriosis, Furunculosis, Yersiniosis, Tenacibaculosis) [4]
Identification of the causative disease agent The bacteriological analysis led to the identification of Tenacibaculum dicentrarchi as the most likely causative agent of the ulcerative disease
Summary
Infectious diseases cause significant production losses in aquaculture every year. Since the gut microbiota plays an essential role in regulating the host immune system, health and physiology, altered gut microbiota compositions are often associated with a diseased status. As reported by the Food and Agriculture Organization of the United Nations in a 2018 report [1], in 2016 the global aquaculture production was 110.2 million tonnes with a firstsale value of $243.5 Billion (USD). Despite the remarkable growth of the aquaculture industries, The United Nations Food and Agriculture Organization forecast a global seafood shortage of 50–80 million tonnes by 2030 [1]. As the world population grows, and the demand for seafood increases, the importance of sustainable food production comes with the need to further optimise sustainable farming practices including improved fish health and growth performance. Fish diseases are a cause of major production losses every year in the world of aquaculture [3] and many of them are caused by bacterial pathogenic infections (e.g. Vibriosis, Furunculosis, Yersiniosis, Tenacibaculosis) [4]. With the rise of the antibiotic resistance crisis, sustainable alternatives for disease control are gaining momentum [5]
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