That being said, ive raised plenty of 'shoal' fish solo. Ime, solo raised piranhas are meaner and more outgoing.
I always thought a solo rbp was shy and skittish without rbp tank mates to shoal with, we've had a few members over the past keep one alone and they always hid and were much less active. But I'm sure with your p keeping xp you can make it the opposite! Look forward to picking this up in 6 months

Go S. Vettel #1 rb8