A fish is an aquatic animal that belongs to the kingdom Animalia and the phylum Chordata. Most fish are vertebrates, meaning they have a backbone, and they are further classified into the subphylum Vertebrata. Fish are characterized by their gills, fins, and scales. They live in water, whether freshwater or saltwater, and rely on gills to extract oxygen from the water.
Fish are cold-blooded, meaning their body temperature adjusts to their surroundings. They play a vital role in ecosystems by being part of the food chain and contributing to the balance of aquatic environments. With over 34,000 species, fish are among the most diverse animals on Earth.