Is my oto chubby, pregnant or sick?
 

One of my Oto's has a plump little belly on heralmost exactly like this fish here:

http://www.otocinclus.com/images/fatoto1.jpg

I'm not sure if she is a female, but she is bigger than the other one and I believe females are bigger and plumper than males so I am assuming she is a she. She looks almost exactly the same shape as the picture, but I haven't been able to get a good long look at her up against the glass. Is she just eating more than the other one, is she sick or is she pregnant? They've been in my pre-established ten gallon tank for about a month now with my male betta and they have both grown substantially since I first picked them up. I figured they'd be hardy since they were the last two in their tank of a shipment at the petsmart I go to. There is no redness from what I can see and she seems to be eating and pooping like crazy, which I know are good signs. Also she is very active and interacts with her friend as normal. Any thoughts?

I have seen some of my otos very fat from time to time, either from eating or from eggs (they readily spawn, though you are unlikely to see fry as they get eaten by other fish). I wouldn't worry.

I agree with Byron, and that picture looks like a very healthy oto to me. :-)