Correct spelling, explanation: in Old English, the plural form of fish was fiscas, which referred to multiple fish. However, as Middle English developed, the plural fishes also began to be used to refer to multiple fish, particularly in more formal or specialized contexts. This usage has persisted, alongside the singular fish, to describe multiple fish. Remember that both fish and fishes are correct, but the second form is often used when it comes to different species of fish.

Definition of fishes:
noun (plural), used to describe more than one species of fish
The marine biologist conducted a comprehensive study of the fishes inhabiting the coral reefs in the Pacific Ocean.
The exhibit at the Natural History Museum showcases a wide variety of exotic fishes from around the world.

Collocations with fishes:
Some most commonly used collocations include:
1. Marine fishes: refers to fish species that inhabit the ocean or other saltwater environments.
Marine fishes are adapted to live in saltwater and have unique physiological features.
2. Freshwater fishes: describes fish species that live in freshwater environments such as lakes, rivers, and ponds.
Freshwater fishes face different challenges than their marine counterparts in adapting to changes in water quality.
3. Tropical fishes: relates to fish species native to tropical regions, often characterized by vibrant colors and unique adaptations.
The aquarium is home to a stunning collection of tropical fishes.
4. Native fishes: refers to fish species that are naturally found in a particular geographic area or ecosystem.
Conservation efforts focus on protecting the habitats of native fishes.

Correct spelling, explanation: the reason fish can be both a singular and plural noun is rooted in the historical development of the English language and its flexibility in adapting to different linguistic situations. In modern English, both fish and fishes can be used to describe multiple fish, but fish is more common and versatile, used in everyday speech and writing. Fishes is typically reserved for more specialized or scientific contexts when discussing different species of fish.