This all depends on what type of other fish you have in your tank. Iridescent sharks are not aggressive fish so if your other fish are aggressive that's your problem
well... when given the space and right diet the iridescent shark can reach up to 4ft long and way up to 100lbs. so u pretty much have ur hands fun there. but in tanks they usually stay around 6-12". in reality catfish never stop growing.. cuz theyre catfish. good luck