'bagre' originates from Spanish (and Portuguese) 'bagre', ultimately entering Iberian languages from Medieval Latin/medieval Romance forms related to the Greek word 'bagrós' (βαγρός), which denoted a type of fish.

'bagre' changed from Portuguese/Spanish 'bagre' which derives from Medieval Latin/Old French forms (e.g. Medieval Latin 'bagra' or similar), and this in turn came from Ancient Greek 'bagrós' (βαγρός); the exact ultimate origin may be pre-Greek or from other Mediterranean substrate languages.

Initially it referred generally to a certain kind of fish in Greek and medieval usage; over time in Spanish it came to be used specifically for catfish and has kept that basic meaning.