Application of method
The results of the present study demonstrate that RNA sequencing of
epidermal mucus can generate a wealth of information on molecular
differences among wild fish populations without the use of lethal
sampling. Although the populations considered in the present study were
located in closely-situated, ecologically-similar lakes, our method was
still able to clearly separate individual transcriptomic profiles by
lake. Sequencing of mucus could be useful in comparative transcriptomic
studies of populations residing in ecologically different conditions,
such as studying ecologically-divergent populations residing in two
different habitat types or comparing a reference population to one at a
polluted site. Moreover, using mucus for gene expression analysis can be
applied to various freshwater and marine species as mRNA-based mucus
analysis has been successful in mahi-mahi (Greer et al., 2019), channel
catfish (Ren et al., 2015), largemouth bass (unpublished), and now lake
trout. As mucus sampling is nonlethal, transcriptomic studies of mucus
would be of most value to studies concerned with threatened and
endangered fish species. mRNA-based analysis of mucus can be used in
conjunction with other nonlethal sampling methods, such as blood
sampling for biomarkers of interest, as well as individual- and
population-level metrics (e.g. through eDNA sampling (Adams et al.,
2019)) to gain insight on health at multiple levels of biological
organization.