The objective of this study was to evaluate welfare and health effects following single and repeated non‐lethal blood sampling from the caudal vasculature of Atlantic salmon. Two experiments were conducted at three different temperatures: a 6‐week freshwater experiment with fish weighing 50–100 g, undergoing up to four blood withdrawals, and a 4‐week seawater experiment with fish weighing 300–450 g, undergoing up to three bloo...