The delicacy, tuna, is usually kept at around -55 degrees Celsius. In fact, tuna can also be eaten after being refrigerated at 0 to 4 degrees Celsius, but if refrigerated, the flesh of the tuna will only remain fresh for 3 to 4 days. In contrast, its quality can be fully maintained for a longer period of time under frozen preservation conditions below -50 degrees Celsius. The average fish can be kept fresh by keeping it at about -20 degrees Celsius, but tuna is special. Tuna is red, mainly because it is rich in myoglobin, this protein is very sensitive to temperature, in different temperatures, the change is also very large. If the temperature is a little higher, the color of the tuna's meat will change, from fresh red to dark red, the view is not good.