i just read a cool article online about aquaculture and they raised talipia fish and used the water to grow vegetables hydroponic and they would sell the fish to resturants in local area. it could work.
Walruses breed easily in captivity and there is high demand for them both for fancy restaurants (walrus is a delicacy comparable to whipped cream with eggs and tofu or a muddy cabbage and bacon pie) and as exotic pets for the wealthy.
You could try maggots and sell them to anglers. The operation might get a bit stinky though.
Breed cats cost an arm and a leg.
Breed dogs then maybe? Or hens? Can't think of anything else that can live in a garden and would make you a reasonable profit. Maybe an ostrich? I had a neighbour once who had a couple of ostriches and sold the eggs to restaurants.
I don't think there's much $ in small livestock operations these days.
will you consider duck?
mice - for the snake owners of the world
Snails if you are in France. Rabbits should never be eaten because they are people too.