Pomacea spp. are essentially
incompatible with fish, so the right thing to do is keep them in their own aquarium. The main problems are their temperature requirements and the ease with which they're damaged. The
Pomacea spp. we keep are subtropical rather than tropical. That's why they are often sold as coldwater animals even in the UK. While you would't keep them in a pond, a room temperature aquarium could be ideal. At the very least, you do need a definite cool period for a few months in the year where they can slow down and maybe even go dormant (though temperatures below 18 C will kill them eventually, so should be avoided). The upper temperature for them shouldn't be much above 24 C, and ideally keep them between 18-22 C.
As for what fish do to them, it's the nipping!
Pomacea have tentacles that look like food, and fish seem to find it difficult to avoid nibbling at them. Eventually the stress and/or bacterial infections weaken the snail, leading to their death.
It's very rare to see
Pomacea in tropical aquaria lasting more than a year. In the wild they can live 4-5 years and reach amazingly large sizes you rarely see in aquaria. There's a good book called "Apple Snails in the Aquarium" that provides plenty of background information on these snails as well as useful advice on keeping them. It's a thick book and not aimed at beginners, but if you really want to keep these snails well, it's a great read.
Once you have the right conditions, these snails are easy to keep and breed like mad. At one point I was using the offspring as live food!
Cheers, Neale
ive tried twice to have a mystery snail in my tank ... he seemed fine for 3 days then the next floating at the top . anyone know why?