Sample collection
At the time of sample collection, fish were removed one at a time from the tank and quickly euthanized [28]. The caudal peduncle was severed and blood collected in non-heparinized capillary tubes and transferred to 0.5mL centrifuge tubes. Tubes were kept at room temperature (RT) for 30 minutes to allow for blood clotting and then centrifuged for 10 minutes at 1000g. Serum was removed to labelled 0.5mL centrifuge tubes and stored at -80°C. Fish were then weighed and total length recorded. Gill epithelium was scraped off with a slide coverslip, placed in aluminum foil, snap-frozen in liquid nitrogen, and placed in -80°C storage. Blood serum osmolality measurements were made using undiluted serum when possible, and diluted with pure water (Optima LC/MS Grade, Fisher Chemical) when necessary due to low volume, with osmolality readings multiplied by the dilution ratio. Osmolality was determined using a freezing-point micro-osmometer (Advanced Instruments model 3300).