Not sure if this is the right spot especially since I have been away for a while but I have two beautiful Adult Red Belly Pirhanas. Believe it or not I have had them for 10 years. They were the size of a quarter when I got them. I'm not planning on selling the tank they are in but it is a 100 gallon custom acrylic just to give you an idea what size aquarium they are in. FREE to a good home.
Feeder goldfish isn't the best thing to feed them although I offer it on occasion. The turtle pellets are best as they are cheap and the Pirhana's love them. I had an arrowana once and you're right, I could only get it to eat live crickets or fish.
Wow. I never realized it wasn't common for them to eat pellets. I found out by accident as I kept a small turtle in the tank with them when they were smaller. The rest is history. I should mention the brand for the pellets is Reptomin.