As Wing said, I wouldn't want to shoot an 80# compound for fish. (this from a guy who usually shoots a 70# recurve) I can only imagine how much time you'll spend digging your arrow out of the bottom unless you're shooting in very deep water.
As far as arrows go, no one spine tests arrows any more 'cept a few of us old guys. but we took a selection of fiberglass fish arrows and ran them through my spine tester. The flimsy-est of the group measured 85# plus. The heavier ones were in the 110 to 120# range. We did not try the Cajun "yellow jacket" which is supposed to be heavier spined or the Muzzy "predator" arrows which is a fiberglass arrow inside an aluminum shaft.

All that to say, I wouldn't be afraid to shoot a fiberglass fish arrow out of any poundage bow. I'd be more afraid of the plastic nock breaking.