I don't think the fish tank bacteria have enough turnover to make independent evolution of ammonia digestion a likely explanation for your particular fish tank. By the time they "won the lottery" and started breaking down ammonia, your fish would have been dead for centuries.
Ammonia – fish produce ammonia as a waste product. It is poisonous and a build up will harm the fish. During the cycling of a new fish tank bacteria are encouraged to grow that convert the ammonia, first to nitrites and then to much less harmful nitrates. Ideally ammonia level should always be zero.