Biting fish swallowing angler’s last insect (9)
I believe the answer is:
trenchant
'biting fish' is the definition.
'trenchant' can be an answer for 'biting' (I've seen this before). I am not certain of the 'fish' bit.
'swallowing angler's last insect' is the wordplay.
'swallowing angler's last' becomes 'trench' (I can't explain this - if you can you should believe this answer much more).
'insect' becomes 'ant' (ant is a kind of insect).
'trench'+'ant'='TRENCHANT'
(Other definitions for trenchant that I've seen before include "Acerbic" , "blunt" , "Incisive in expression" , "Clear-cut and hard-hitting" , "Cutting, forthright" .)