Is there a fish group called shellfish?

Shellfish is not a taxonomic term but rather a common name used to refer to various types of aquatic animals with hard external shells. While some shellfish, such as shrimp, lobsters, and crabs, are crustaceans, others, like oysters, clams, and mussels, are mollusks. Therefore, shellfish do not form a cohesive group within the classification system of animals.