A bleeding method for a fish includes step of forming a slit SL that connects pericardial cavity 11 to an outer part of the fish by cutting membrane 16 to split a head and an abdomen such that abdominal aorta 19 is not cut and internal organs incorporated in abdominal cavity 12 are not exposed to an outside air, step of spreading the slit such that arterial sphere 18 does not tomozure, and a caudal side surface of ventricle 171 is exposed, step of inserting tubular instrument 2 in heart 17, which runs through the spread slit SL from the caudal side surface of the ventricle toward arterial sphere 18, step of fixing tubular instrument 2 to heart 17, and step of discharging blood of the fish outside by press-fitting liquid into vascular system of the fish via tubular instrument 2.