Fairly loud animal? (4)
I believe the answer is:
'fairly loud animal?' is the definition.
'fish' can be an answer for 'animal?' (I have seen 'Aquatic animal' mean 'fish' so perhaps 'animal' could also mean 'fish'). I'm unsure of the 'fairly loud' bit.
'loud animal?' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'animal?' becomes 'ish' (I am not sure about this - if you are sure you should believe this answer much more).
Can you help me to learn more?
(Other definitions for fish that I've seen before include "counter in various games" , "Ruff" , "Burbot or turbot, for example" , "occupant of tank" , "Aquatic creature; rail-joining plate" .)