In the field of fish physiology, the species-specific parameters of blood, biochemistry, and hormones are especially unknown. The main reasons for this include difficulties in drawing blood from some fish species and nonstandardized blood reference values that change for fish weight, water temperature, and other environmental variables. Information and instructions for drawing blood from fish are limited, and there are few practical examples. Fish blood should be studied to determine metabolic disease and feeding disorders and also to improve rapid diagnostic kits for determining microbiologic diseases. This paper demonstrates methodologies for drawing blood from both aquarium and farmed fish and lists the advantages and disadvantages of each procedure, considering animal welfare and practicalities. Images and videos showing the different applications are also presented.