Evaluating Sampling-Induced Stress in Atlantic Cod (Gadus morhua)

Atlantic cod, Gadus morhua, have historically been regarded as one of the most commercially and recreationally important fishes in the Gulf of Maine. All fish involved in fishing and aquaculture are subject to stress, indicated by elevated plasma cortisol concentrations. Given the amount of research conducted on Atlantic cod, stress, and cortisol, little has been done to compare different blood sampling methods and the effects they might have on plasma cortisol concentrations, particularly in adult fish. This study examined three different methods of repeated blood sampling (standard handling caudal vessel puncture, reduced handling caudal vessel puncture, and cannulation) in Atlantic cod and determined if sampling method affected plasma cortisol concentrations. Plasma cortisol concentrations differed significantly between the dates on which the samples were taken, and between the methods of sampling. Vessel puncture blood samples taken using a reduced handling method usually produced lower plasma cortisol concentrations than those obtained via standard methods of handling. Repeated caudal vessel puncture samples, taken 72 hrs apart, did not always produce plasma cortisol concentrations similar to those of the original pre-stressed sample. Furthermore, repeated sampling via cannulation was able to generate plasma cortisol concentrations similar to baseline concentrations 48 hours following surgery. These results highlight the importance of reducing sampling induced stress when taking blood samples for plasma cortisol analysis