5 of the 7 are this fat. My GF thinks they're all preggers, but I'm not so sure. I think they're just well fed and fat. They had lots of diatoms to feed on when I first got them. They pretty much handled it all in the last 2 weeks though.
These are the first otos I've kept so I'm far from a pro, but I'm guessing as long as they are active swimmers and are always hunting for something to graze on, they're healthy. I don't think fat should be the norm for an oto. Its just a sign of a VERY well fed oto.
I have noticed mine are fat too... I had thought the same thing if they were prego or full of eggs or what...never thought about breeding them so I don't know the facts on that... just know they are sensitive and you can look at their bellies to tell if they are getting eoung to eat......yayyyy our oto's are getting enough....
Mine just look like they have pot bellies but not really that visible when viewed from the side like in your photos.
Like I said they seem happy. Surprisingly I got 3 of them from Petsmart maybe 6 months ago and all survived. They did go into my 10 gal tank first that had some algae for them to eat and quarantine before moving into my 20 gal. At first they seemed to love eating the zucchini but not so much anymore. And I did put some plants into that tank from my 75 gal that had brown diatoms on them which they really love to eat. It's possible some of the diatoms got on the substrate and that could be what they're eating now.
Great fish, I love them. All they do is work and get along with the other fish - can't beat it!
I have 10 in a 210 gallon and they do surprisingly well keeping it clean. Obviously it is too much to keep it perfect but they are always fat. When I had diatoms they would clear a 6in x 6in patch on my rocks overnight.