Author: Analisa Lazaro-Côté
Non-invasive sampling methods are essential for species of conservation concern, where legal protections often restrict lethal tissue collection. Bull trout (Salvelinus confluentus), a cold-water stenotherm listed under Canada’s Species at Risk Act, are experiencing population declines and range contraction attributed to rising stream temperatures, among other stressors. Because fish epidermal mucus can be collected rapidly (<1 min) and non-lethally, we tested its utility to detect transcriptional thresholds of thermal stress compared to lethally sampled tissues traditionally used in transcriptional profiling. Eggs were collected from a wild, montane population in Alberta and reared at the Fisheries and Oceans Freshwater Institute, Winnipeg, Manitoba. Two-year-old fish were acclimated to 9°C, 12°C, 15°C, or 18°C for four weeks, following which mucus, gill, liver, and muscle were sampled and the transcript abundance of 56 genes was measured. Mucus and gill transcriptional profiles correlated most strongly, both indicating a thermal threshold at 15°C. Our results indicate that epidermal mucus can be used to identify individuals experiencing thermal stress and that this minimally invasive approach is well-suited for monitoring wild bull trout. We selected 28 genes most sensitive to thermal stress to develop a mucus-specific STP-chip, allowing us to screen 48 individuals in duplicate rather than 24 on a single chip. Through collaborations with fRI Research, a conservation NGO, and Fisheries and Oceans Canada, we are deploying this tool across wild bull trout populations in Alberta and the Northwest Territories. Our approach holds promise to identify thermally unsuitable habitats and support conservation efforts. To expand this framework, we are developing additional omics resources, including a de novo mucus transcriptome (RNA-seq) and the identification of epigenetic markers (small RNA-seq) associated with thermal stress to enhance our understanding of regulatory mechanisms underlying thermal acclimation in this climate-sensitive species.