What is Wrong with My Oto?

[Dr. Fish]

I have had my fish for about 2.5 weeks. I have a betta, some lamb chop rasboras, and three otos. Everything has been fine except that the last few days I noticed that one of my otos rarely moves and just lays around on the bottom of the tank. It is alive as I see its gills move and I have seen it move position in the tank recently. However, I don't think it is eating. The other two have large, round bellies and are constantly eating. This one has a sunken in belly (see oto on top right in the pic). I have algae growing on the plants in the tank and I put in algae pellets for the otos every few days. Any idea why it won't eat and what I could do to get it to eat? TIA! 

I just did a water change (it was time), but when I checked my water parameters yesterday things looked fine. 

[Dr. Fish]

Also, I'm new to the forum. I hope this is the correct forum, I apologize if it should be in another one. 

[lefty o]

its possible he has an internal parasite.

[Colu]

It looks very thin it could be internal parasites or it not getting enough food have you seen it eating 

Edited May 15, 2021 by Colu

[Dr. Fish]

Thank you those who responded. He is gone. 😞

I bought some meds to treat parasites incase that is what the cause was. I don't want it to spread to my other fish. 

[Tami]

so sorry for your lose. I love Otos.

[Gator]

You said that your water parameters are fine and that is great, but you didn't say what your water temp is. I keep all of my tanks temps between 81 and 83 degrees, most tropical fish diseases can't survive temps over 80 degrees. I remember back in the '80's when fish meds used to require that you raise your water temp to 85 degrees during treatment, the 85 degree temps didn't hurt the fish, so I save a boat load of money by keeping my temps above 80 degrees.