Wow, all this about OTOS, and now I am wondering, too. I have never lost an OTO yet. Mine have lived for more than 3 years so far. I have no idea why either since I switched tanks from a 55G to a 29G and brought the same OTOS with me. Does anyone know what a healthy, happy OTO's lifetime span is?
I, too, think these little guys are not only cute as can be but also an essential part of a planted tank. They are little workers on algae for sure. I also put in zucchini once a week right after a 50% water change. I think of it as a "treat" for them for being so calm during the water change. And during the night, all 3 of them can be seen going to town on the zucchini. I don't leave it in there the next day, though. I am afraid they will over eat along with the Plecos.