Was fishy (or ratty?) (5)
I believe the answer is:
smelt
'ratty?' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs can sometimes mean the same thing.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for smelt that I've seen before include "Small fish of salmon species" , "were high" , "Extract metal from ore, fish" , "Extract metal from twenty two" , "Arab leader" .)