The correct answer is two.
Fishes have a two-chambered heart, which consists of an atrium and a ventricle. The atrium receives oxygen-poor blood from the body and pumps it to the ventricle. The ventricle then pumps the blood to the gills, where it is oxygenated. The oxygenated blood is then pumped to the rest of the body.
A single-chambered heart would not be able to effectively separate oxygen-rich and oxygen-poor blood, which would make it difficult for the fish to survive. A three-chambered heart would be more efficient than a two-chambered heart, but it would still not be able to completely separate oxygen-rich and oxygen-poor blood. A four-chambered heart is found in mammals and birds, and it is the most efficient type of heart.
Here is a diagram of a fish’s heart:
The atrium is the upper chamber of the heart, and the ventricle is the lower chamber. The atrium receives blood from the body, and the ventricle pumps blood to the gills. The gills are where the blood is oxygenated. The oxygenated blood is then pumped to the rest of the body.