Gutted French fish produces toxin (6)
I believe the answer is:
poison
'toxin' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for poison that I've seen before include "Damaging stuff - drink?" , "Toxic substance" , "[ADDER] 's defence" , "Corrupt" , "Dangerous substance" .)