Why does oxygenated blood reach the muscles and organs more rapidly in amphibians than it a fish?

This statement appears to contain a misconception. In general, the circulatory systems in fish are more efficient at transporting oxygenated blood to the muscles and organs compared to amphibians.

Fish have a closed circulatory system, which means that their blood is contained within vessels. This allows for a more efficient and rapid distribution of oxygenated blood to the body's tissues.

In amphibians, the circulatory system is single, meaning that oxygenated and deoxygenated blood mix within the heart. This can result in lower oxygen delivery to the body's tissues compared to fish.

Additionally, amphibians have a lower heart rate and cardiac output compared to fish, which further limits the rate at which oxygenated blood is pumped to the muscles and organs.