How big do shovelnose catfish get??

Would they be comfortable in a 120 gallon tank

They get extremely big. Ironically, I was looking at three of them today as the local aquatic Centre. I suppose the biggest one was around 18 inches long. And why were they all at the aquatic centre? Because people bought them as babies not knowing how big they get. I should forget one of these fish if I was you, I don't even think 125 gallon tank is really big enough for one of these.

what about a bichir or two¿?
or maybe 2 clown loaches¿?

or would they both get along??

Actually, it depends on which kind of shovelnose. There are two common types in the hobby-

The tiger shovelnose catfish, and the lima shovelnose catfish. The Tiger can get three feet and are not very aggressive fish when young, I have a difficult time getting food to my tiger with my younger oscars constantly crowding around and sticking there faces out of the water. The lima isn't aggressive either, but gets 16'' max, there are few specimens I know of over 20 inches, but this is rare. A lima could go in a 120 depending on the dimensions. I'm assuming it's a 48x24x24? As well as these two common species, there are also several more uncommon species and similar catfish such as the marbled pim (which isn't really that hard to find), and many others. These catfish are called south american antenae catfishes, or "pims"

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