my dads solo red belly piranha. No school and only in a 55g. He also feeds it steak and lunch meat :0 can't teach a old dog new tricks so I gave up. He does keep up with water changes. I can't believe it's still alive. He wants to know how long it will live?
Honestly, that fish could have it way worse than steak and decently clean water in a 55g. Maybe you could convince him to feed it small crawdads now and then? Entertaining for him, nutritious/enriching snacks for the piranha.
Those guys can live 10-15 years, I believe. They're pretty long-lived fish.