Make sure you check the legality of this, I don't mean to be a wet blanket, but you should check. I once had some minnows I was gonna put in a fish tank, and was told by a game warden that this is illegal. You can catch them, kill them, but you can't keep them for pets. I learned to check for everything before doing it. I hope it is legal, cause it should be, but you never know.

As far as the drop mechanism goes, check out the flat line clips that they use in offshore fishing boats, or maybe an outrigger release clip, it could be fashioned to work with a servo and would open with a set amount of pressure, which is adjustable.

Good luck,
I've caught carp up to 60 lbs in the pocomoke river, and they fight hard. Don't appologize for fishing for them, there tougher, smarter and harder to catch than any bass ever is.
Kurt