South American Fish

Question
Me and my wife recently bought 3 SA fish.  A clown knifefish, a lima shovelhead cat, and a gar (feshwater barracuda).  We have a pleco in there as well for algea.  They live in a 55 gallon tank but for some reason they all just sit in one corner of the tank .. every now and then we catch em sliding over to the other side but as soon as they catch our movement they jump back to the corner. I should also mention that they are all about 8 inch long.  For my question and concern.  Is the whole staying in a corner thing natural? like territorial? Also my concern is that I think the gar is eating all the food before the knifefish can get any. It also seems that the knifefish only eats live food now, even though the guy at the pet store said he raised it and fed it krill every other day and goldfish once a week. I guess what im trying to conclude is should there be anything I should really be watching out for?  

First time SA fish owner.

Answer
The clown Knifefish, shovelhead Cat and Gar all need to be kept in a tank larger than 55 gallons, they are also incompatable due to territorialness...I would rehome them and go with more traditional SA fish like angelfish, tetras, rams, etc...the corner thing means the fish are not happy and are afraid of each other...how would you like to live in a house where everywhere you turned you feared for your life