Fish found in the east by the Spanish (3)
I believe the answer is:
eel
'fish' is the definition.
(eel is a type of fish)
'east by the spanish' is the wordplay.
'east' becomes 'e' (abbreviation).
'by' is a charade indicator (letters next to each other).
'the spanish' becomes 'el' ('the' in Spanish).
'e'+'el'='EEL'
'found in the' acts as a link.
(Other definitions for eel that I've seen before include "Sea creature like conger" , "slipper" , "Teleost fish" , "Large elver" , "A sea snake" .)