Abstract
The skin of the teleost is a flexible and scaled structure that protects the fish toward the external environment. The outermost surface of the skin is coated with mucus, which is believed to be colonized by a diverse bacterial community (commensal and/or opportunistic). Little is known about such communities and their role in fish welfare. In aquaculture, fish seem to be more susceptible to pathogens compared to wild fish. Indeed common fish farming practices may play important roles in promoting their vulnerability, possibly by causing changes to their microbiomes. In the present study, 16S rRNA gene amplicon sequencing was employed to analyze the composition of the farmed Salmo salar skin-mucus microbiome before and after netting and transfer. The composition of the bacterial community present in the rearing water was also investigated in order to evaluate its correlation with the community present on the fish skin. Our results reveal variability of the skin-mucus microbiome among the biological replicates before fish handling. On the contrary, after fish handling, the skin-mucus community exhibited structural similarity among the biological replicates and significant changes were observed in the bacterial composition compared to the fish analyzed prior to netting and transfer. Limited correlation was revealed between the skin-mucus microbiome and the bacterial community present in the rearing water. Finally, analysis of skin-mucus bacterial biomasses indicated low abundance for some samples, highlighting the need of caution when interpreting community data due to the possible contamination of water-residing bacteria.
Highlights
The body surface of vertebrate animals represents a physical barrier between the environment and the animal host
The bacterial community in the tank water was characterized to evaluate its influence on the skin-mucus microflora
The number of 16S rRNA gene copies obtained from the skin-mucus varied between individuals (Figure 3 and Supplementary Table S2), showing low biomass in some samples, which may be related to low bacterial biomass in the mucus (Austin, 2006), technical challenges in the DNA extraction procedure or a combination of these
Summary
The body surface of vertebrate animals represents a physical barrier between the environment and the animal host. The presence of a mucosal tissue on fish skin represents an evolutionary adaption to the water environment (Xu et al, 2013), which is populated by a large. In contrast to the well-studied human skin microbiome (Schommer and Gallo, 2013; Dorrestein et al, 2016; Gallo, 2017) only a limited number of studies have focused on the complexity of the bacterial community associated with the fish skin-mucus (Llewellyn et al, 2014; Chiarello et al, 2015; Lowrey et al, 2015; Lokesh and Kiron, 2016; Kearns et al, 2017). Chiarello et al (2015) reported variability of the skin-associated community between host species, individuals and as well among different external body parts. When comparing the microbial community of skin, gills, olfactory rosettes and anterior and posterior gut tissues from rainbow trout, Lowrey et al (2015) observed that the highest microbial diversity was found in the external mucosal sites of fish
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