I disagree that the indefinite article is needed, or even should be used at all. "Pez" would typically be used for indicating "a" singular fish or multiple live fish, and the article would be required in English. Pescado, on the on the other hand, is dead, ready to be eaten fish - one or several- , so using "pescado" is like saying we are having fish for dinner; In English you wouldn't say we are have A fish for dinner. Yet that is the Duoligo required answer. Seems wrong to me.