I have 3 otos. 2 older ones that became extremely shy, and one I have acquired recently (and which has come with extra gift of ick, LOL).
I am giving them cucumber and Hikari Mini Algae wafers.
The old otos became very shy, just hiding on the back wall of the tank behind the heater or plants of driftwood, I do not ever see them eat.
The new oto is always next to feeding dish munching on the algae wafers or sometimes eating the cucumber.
There is a ton of algae everywhere, especially on Anubias leaves, but some of it seems very hard - I have hard time scratching it off with my nails. The snails seem to eat it, but I don't think otos do. Every time I change the cucumber bit, I throw away several snails. But they keep coming ;-)
I fear that my shy otos are going to starve. I don't know how to change their behavior and make them eat and come to the front of the tank.