It hasn't been fed properly then. It should be huge by now
It might not be a redtail catfish. There are a couple of smaller catfish that have a red tail and it might be one of them but without a side view of the fish I won't guess as to if it's something else. The tail definitely looks like a redtail catfish tho.
Do you know someone with a heated freshwater swimming pool?
see if they want it
The poor fish looks very undernourished
Here is a profile on the red tailed catfish http://www.seriouslyfish.com/species/phractocephalus-hemioliopterus/
I was in one shop a few years ago which had a red tailed catfish in the largest tank they had, about 4 feet long. The fish was almost as long as the tank, and couldn't turn round. Someone had literally dumped the catfish on their doorstep and they were desperately trying to find a home for it. The shop closed a short while later so I never discovered what happened to the fish.