Iridescent Shark

[Soaup]

Ok so i went to a Mom and pop petstore today where i found many many tanks badly over crowded. I saw a 30 gallon tank with three massive Iridescents A very large Red bellied Pacu and Several Large Parot fish along with a few more large Koi all in a 30 gallon.. I decided to resue the largest Iridescent and put him in my 125 gallon tank.. Which currently houses an albino channel and florida gar and two suprisingly peaceful oscars.. The oscars have never beat up on one another nor any of the other fish. Well anywyas the New guy is about 11 inchs which is slightly smaller then the albino and the gar who are about 14-16 inchs each.. I know my tank is getting close to over stocking itself but i figured he would have a better chance in life in my tank then sitting in the 30 gallon. Well anyways His introduction to the tank was not a good one.. He was chased by the gar who did not all become bitey just chased him i guess to establish dominance.. The catfish however was bitey and was taking little nips and such.. He seems fine now but im just curious if this will become a long term problem?? They guy from the petstore said I have plenty of room... Well this is coming from someone who cant run the store properly and he said just feed your fish before you add the Shark which is what i did.. I know the Shark is a catfish so i figured him and the albino should be fine together.. I have had the catfish for sometime now and he usually terrorized my fish for the first 10-15 min then they become the best of friends.. Any advice would be great.. Thanks.. Also i have pelet food which all but the gar eat.. That should be fine for the Iridescent right?