Mine are survivors and I am surprised that they didn't starve to death when I first got them...I am in agreement with everyone else, it depends on the source.
The last dozen Otos I bought I got them from a petsmart. I knew if they could survive a month there, these guys were a tough batch. And they have been, they love hanging out on the ton of driftwood in my angel tank, amost like they are basking in the light.
I have 4 in my 55g and have never lost one. They live only off the algae and are thriving. Their little tummies are always big. I drop in algae wafers but I think the other tankmates get to them first.
i have 9 in my 55. i got them all from petsmart. there were 10 (one i got several months before the others), nine i got within the last month or so. the newer ones were severly undernourished and one died within 24 hours. however (maybe because they were starved), the new ones caught onto the idea of food other than algae within minutes of being in the quarantine tank. they ate almost all of the algae off the glass and then jumped right into algae wafers and zucchini slices and cory wafers and shrimp pellets. now they eat just about anything. the survivors are fat and active.
Sometimes, when you get them, they are very weak. I'm not sure whether this is a starvation issue or that they are overcome by fear. With some of them, I had the feeling that they passed out because they were so afraid.
If they survive this first hurdle, the next difficulty will be to find something they actually eat. I had the same experience as others have already mentioned: Some otos have no problem with eating zucchini or other vegetables, whereas others don't touch anything other than algae. The latter ones might pose a problem.
But those that survive can be with you for many years .
Acclimate them carefully. I put mine in a dark-sided bucket because they stress out so easily from being hung in a bag in the tank (they can't get to shelter and see all the other fish; it stresses them), then drip acclimate for at least an hour.