What creatures or objects usually belong to a shoal?

A shoal typically consists of small fish species, such as sardines, herring, or anchovies, that swim together for protection and foraging. However, other marine creatures like shrimp or certain species of squid can also form shoals. Additionally, the term can extend to groups of similar objects, such as floating debris or schools of plastic waste in water bodies. Overall, the concept of a shoal emphasizes the collective behavior of creatures or objects in a defined area.