Fisherman's profit? (3,4)

I believe the answer is:

net gain

I'm a little stuck... Click here to teach me more about this clue!

'fisherman's profit?' is the definition.
'net gain' can be an answer for 'profit?' (I've seen this in another clue). I'm not certain of the 'fisherman's' bit.

'fisherman's profit?' is the wordplay.
'fisherman's' becomes 'net' (I can't explain this - if you can you should believe this answer much more).
'profit?' becomes 'gain' (synonyms).
'net'+'gain'='NET GAIN'

Can you help me to learn more?

(Another definition for net gain that I've seen is " Profit".)

I've seen this clue in The Globe and Mail and The Irish News.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.