Exercise reeling fish in — it isn't worth much (6)
I believe the answer is:
peanut
But I can't explain it at all! Could you help me understand?
(Other definitions for peanut that I've seen before include "Groundnut" , "grows in the ground" , "Tasty edible seed, often salted" , "One of little importance -- ante up (anag)" , "Singularly little money" .)