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.