... a leopard shark is a salt water-brackish fish that gets 6 feet long.
I'm sure they'll be fine, most fish can tolerate small amounts of salt. I add aquarium salt to my tanks (1/2 tsp per 5 gallons). You could try putting in adult bala sharks, but you'd need at LEAST a 150 gallon tank for that, and that catfish needs 75 as it is. To avoid squabbles (the bullhead catfish is VERY territorial) I wouldn't keep it with other fish in anything less than a 200+ gallon tank. It's small now, but they get 14" and have very big mouths.
EDIT: forgot to mention that balas need to be in schools of at least 5, that's why you need such a large tank. And yes, I know, at Pet Co, they're little 3" cuties, well, they grow.