Quite a few years ago now, I used to keep and also breed tropical fish. Always providing that you kept catfish in a fish tank and no other variety you could nearly always keep a few tropical snails. Ideal for an aquarist because they kept the inside glass of a fish tank clean.
The snails lived in the water never coming out except to lay their eggs. This they did in the cover of the fish tank, then promptly returned to the water. The young snails as soon as they had hatched made their way back down into the tank water. The snails grew to about the size of a golf ball when adult, care had to be taken because a dead snail could very quickly contaminate even a 20 gallon tank. Apart from that it was easy to see that all was good. But it was important to check every time you fed the fish that the snails were fit and healthy.