The Spanish word 'bagre' (meaning 'catfish') traces its origins back to Ancient Greek 'phagros' (φάγρος), which referred to a sea bream. This word was borrowed into Latin as 'pagrus', maintaining the meaning of 'sea bream'. The word then evolved through Catalan 'bagra', which referred to a freshwater fish, before finally entering Spanish as 'bagre'. Notice how the meaning shifted from a specific type of saltwater fish (sea bream) to a freshwater fish, and finally specifically to catfish in Spanish. The sound changes from Greek to Spanish included the softening of 'ph' to 'b' and the simplification of the ending.

While 'bagre' doesn't have many common Spanish relatives, it's worth noting that Spanish borrowed several other fish names from Greek and Latin sources, though they followed different evolutionary paths.

The English word 'porgy' (a type of fish) is actually a cousin of Spanish 'bagre', as it also comes from the same Greek root 'phagros' through a different path. While 'bagre' came through Latin and Catalan, 'porgy' entered English through a different route, but both words ultimately trace back to the same Ancient Greek word for sea bream.