One of the small lakes I like to fish is full of pollywogs. The TPWD website has nothing to distinguish yellowcat from pollywog on the fish identification page. Is a yellowcat a big pollywog?

No a pollywog is a mud cat.That is the way I have always understood it.
Johnny

pollywog = bullhead = mudcat

2-3 lbs. is a big one

flathead = yellow cat
They get big and eat pollywogs.

As far as ID goes...mudcat are usually a shorter, plumper fish, usually pretty much round in cross-section. Their jaws also meet pretty much evenly. The eyes are on the sides of the head. Flatheads tend to be more of a squatty fish, seemingly lean when viewed from the side, and have a strong underbite (bottom jaw sticks out further). Their eyeballs also tend to be more towards the top of the head.

Thank you Catfish Hunter. I didn't know yellows and flats were the same thing. Makes sense now.