I've seen those gobies before some of them get pretty big. The fish I saw was a sucker fish there was know doubt about that. I don't know we're you found out the temperature of the water but during the summer it feels more like 20 C but during the winter it's probably cools down by about 15 degrees. When I go to my cottage in the spring I will try and find one and take a photo. I don't know of any other sucker fish that aren't species of plecos. It's amazing the things we can find in rivers and lakes now. The Trent river is home to many invasive species like the rusty crayfish, round gobies, chinese mystery snails, possibly plecos, and many more.
There are tons of other sucker-mouthed fish in the world. Some aquarium species like Chinese and Siamese algae eaters, flying fox,etc... There are different species of "suckers" in the rivers near my house that arent plecos. It would be cool to get a pic though, definitely interested especially if it had bristles.