I have 6 otos. Only got them only a few weeks ago but I did a fair bit of research on them. When first put into a new tank, and it should be an established one, they will basically feed on the algae in the tank. They do best in a planted tank. They should be offered algae wafers and fresh veggies. Courgette (young zuchinni) spinich, cucumber or romain lettuce. They may ignore it if they are getting sufficient algae, but these should be offered occasionally anyway to be sure. A chubby oto is a happy oto.