Pez vs. pescado
In Spanish, the terms 'pez' and 'pescado' both translate to 'fish' in English, but they are used in distinct contexts. The key difference lies in whether the fish is considered 'alive and swimming' or it has been caught for consumption.
Pez
This word is used to refer to a fish while it is still alive and in its natural aquatic habitat. When discussing marine life or talking about a fish in an aquarium, you would use 'pez'.
El pez nada en el océano.
(The fish swims in the ocean.)
Mi pez dorado vive en una pecera.
(My goldfish lives in a fish tank.)
Pescado
This word refers specifically to fish that have been caught (usually for human consumption). When discussing cooking or eating, we use 'pescado'.
Hoy comeremos pescado para el almuerzo.
(Today we will eat fish for lunch.)
El salmón es un pescado muy popular.
(Salmon is a very popular fish.)
Summary
'Pez' and 'pescado' both refer to 'fish', but in different contexts. Use 'pez' when referring to live, swimming fish; use 'pescado' when referring to fish as food. It's one of the nuances of Spanish language that showcases its rich diversity.