What is a shoal of fish?

A shoal of fish refers to a large group of fish from the same species and similar size, which often swim together for various reasons, such as protection from predators, increased foraging efficiency, and enhanced reproductive success. This social behavior can also help with navigation and locating food sources. When fish are in a shoal, they tend to exhibit coordinated swimming patterns, which can provide benefits like confusing predators or improving their chances of finding mates.

The other options do not accurately define what a shoal of fish is. For instance, a group of different marine species swimming together refers more to mixed-species schooling or aggregations, which is not the same as a shoal that predominantly comprises similar species. The reference to fish living in coral reefs is more about habitat than behavior regarding shoaling. Lastly, an isolated group of fish in a specific habitat suggests a stationary or solitary existence, which contradicts the dynamic and social nature of a shoal. Therefore, the definition of a shoal as a large group of fish of similar species and size fits perfectly with their observed behavior in marine environments.