A bit fishy, but heroes use it (3)
I believe the answer is:
roe
'a bit fishy' is the definition.
I can't judge whether this definition defines the answer.
'heroes use it' is the wordplay.
'heroes use' becomes 'ro' (I can't explain this - if you can you should give a lot more credence to this answer).
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'ro'+'e'='ROE'
'but' is the link.
Can you help me to learn more?
(Other definitions for roe that I've seen before include "Mass of fish eggs" , "Swift runner" , "shy animal" , "Mass of fish's eggs" , "Food from fish" .)