Fish do have blood, and it is red.
Other cold-blooded animals, like amphibians and reptiles, also have red blood.
Fish have a circulatory system with blood and a heart as the pump just like that of humans, and just like that of humans, fish blood is red because it contains hemoglobin, the iron compound that carries oxygen.
If a fish is fresh and is cut near major vessels, you will see blood.
In muscle tissue, which becomes fillets, the vessels are so small that the blood may not be evident, or if the fish is not fresh, the blood may have coagulated or collected in one part of the body.
Fish from the fish market may have already been gutted and beheaded and so may be drained of most blood.
Even so, you might see blood around the spine, because a major blood vessel goes right under the arches of the vertebral column.
