Abstract
Fish skin mucus is composed of insoluble components, which form the physical barrier, and soluble components, which are key for interrelationship functions. Mucus is continuously secreted, but rates of production and exudation are still unknown, as are the underlying mechanisms. Using stable isotope analysis, here, we evaluate skin mucus turnover and renewal in gilthead sea bream, separating raw mucus and its soluble and insoluble fractions. Isotopic abundance analysis reveals no differences between mucus and white muscle, thus confirming mucus samples as reliable non-invasive biomarkers. Mucus production was evaluated using a single labelled meal packaged in a gelatine capsule, with both 13C and 15N, via a time-course trial. 13C was gradually allocated to skin mucus fractions over the first 12h and was significantly (4-fold) higher in the soluble fraction, indicating a higher turnover of soluble mucus components that are continuously produced and supplied. 15N was also gradually allocated to mucus, indicating incorporation of new proteins containing the labelled dietary amino acids, but with no differences between fractions. When existent mucus was removed, dietary stable isotopes revealed stimulated mucus neoformation dependent on the components. All this is novel knowledge concerning skin mucus dynamics and turnover in fish and could offer interesting non-invasive approaches to the use of skin mucus production in ecological or applied biological studies such as climate change effects, human impact, alterations in trophic networks or habitat degradation, especially of wild-captured species or protected species.
Highlights
Stable isotope analysis is a very powerful and effective tool to determine trophic relationships, dietary switching and migrating patterns when studying fish ecology (Maruyama et al, 2001; Church et al, 2009)
Most studies of fish skin mucus have been performed on the soluble fraction, considering isotopic composition (Church et al, 2009; Maruyama et al, 2017; Shigeta et al, 2017)
We studied separately raw mucus and its soluble and insoluble fractions
Summary
Stable isotope analysis (hereafter SIA) is a very powerful and effective tool to determine trophic relationships, dietary switching and migrating patterns when studying fish ecology (Maruyama et al, 2001; Church et al, 2009). Dorsal white muscle is considered the best tissue as it represents fish dietary adaptation isotopically (Martín-Pérez et al, 2013; Busst et al, 2015; Vander Zanden et al, 2015). Early experiments reported that the isotopic half-lives exhibited by these tissues can be longer than those of dorsal muscle (Busst and Britton, 2018; Winter et al, 2019). Limited SIA has been performed on fish mucus, and mostly in freshwater fish species, initial suggestions are that mucus has a relatively fast turnover, similar to or faster than that of muscle (Church et al, 2009; Maruyama et al, 2015, 2017; Shigeta et al, 2017; Winter et al, 2019)
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