Collection of Samples
Epidermal mucus was collected from seven lake trout captured in each of
L260, L223, L224, and L373 in late September/early October 2017. Fish
were captured from a boat using hook and line and, upon capture, were
placed in separate bins of fresh lake water until processing (held
< 5 min). Retrieval and post-capture air exposure were
minimized to reduce physiological stress (Cooke et al., 2013). Water was
renewed for each fish to prevent cross-contamination between
individuals. Prior to collecting mucus, lake trout were placed in a
solution of 0.1g/L pH buffered (7.0) tricaine methanesulfonate (MS-222)
mixed in lake water until fin movement ceased and fish were unresponsive
to light pressure on the caudal fin. Total length, fork length, weight,
and sex of the individuals were recorded. Sex was determined through
external morphological characteristics if possible, or by expressing a
small volume of gametes through gentle pressure on the abdomen. Mucus
was collected by gently scraping the skin with a stainless steel
spatula, avoiding displacement of scales, to aggregate the mucus along
the body axis in the anterior to posterior direction. The aggregated
mucus was aspirated using a syringe, dispensed into a microcentrifuge
tube, placed on crushed dry ice, and stored at -80°C until analyzed. All
tools and work area were cleansed with 95% ethanol between fish to
prevent cross-contamination of mucus.