Pleco has sunken belly

Hi. This is my first time here, but I need help. My BF bought me a common pleco in February. He was not aware of how big they get when he bought him. After his massive growth spurt, I decided it was time to buy a larger tank, not the 20 I had, so I purchased a 50-gallon tank (I know still not big enough) and used a quick start, and let it cycle for about two weeks. I then transferred my Pleco. He has been in the new tank for 2-3 weeks now, and I have noticed some strange behavior since he was added, but chalked that up to a new environment.
Now, to the point. Yesterday he was on the front of the tank, and I noticed his belly was sunken in! I started to panic a little. I don't want to lose him. He has been eating wafers and zucchini (the same diet since I got him). I have noticed he isn't eating as much as he used to. I also had noticed, for a while, that when he is on the walls of the tank he constantly slides down. He has also been swimming in a bit of a frantic manner. He always did that here and there but now it seems much more often.
I am not sure what I should do, or if there is anything I can do. I certainly hope I did not decide an unfortunate fate for my pleco without realizing what I was doing. If anyone can help I would be greatly appreciative!!

 

Hi,

Sunken belly could be intestinal parasites. Does he also have white stringy poo?

I had made some comments in this thread earlier. Read through this thread:
Platy looking really weird | Platy Forum | 506243

 

Could be worth feeding him some extra protein. Catfish pellets or even soaked flake.

Although if you have other fish in with him chances are he is allready getting some.

 

Actually I take that back probably not intestinal parasites its probably being in a new tank. This happened to me once. I had a 13 year old red tail shark and after I moved him to a upgraded cycled tank it died shortly after. I would move him back into the old tank (if its still running) asap where he may have a chance to recover.

Also check the poo to see if its white and stringy (a sign of intestinal parasites).

 

Thank you both. I do have one other fish in the tank with him. He is definitely eating. I dropped a zucchini in, and he was eating it right away. I already took the old tank down, and have been kicking myself since. I originally was going to leave it up, for a while anyway, just in case, I needed it for something. I Had an Ick problem right after I got the pleco, and I didn't want to use anything from the tank in case any of it remained. I looked at him as best as I could last night, and he looks healthy otherwise. No discoloration or other visible marks. I tried to look at his belly again, but he wouldn't go where I could see. Hopefully, it is just stress and he comes around. After the Ick, I knew he was a fighter.