Which part of the circulatory system serves to supply blood to the heart muscle itself?

Given below are two statements regarding the circulation of blood in fishes.
Statement $I$: The heart of a fish contains only deoxygenated blood.
Statement $II$: Fishes show single circulation,and blood passes through the heart only once during each cycle.
In light of the above statements,choose the correct answer from the options given below.

$A$ portal system is one in which

How many times will a red blood corpuscle $(RBC)$ have to pass through the heart in its journey from the hepatic artery to the aorta?

In reptiles and amphibians,there is no clear-cut separation of oxygenated and deoxygenated blood because they have

In an open circulatory system,where does the blood flow into the body?