Your tank is pretty stocked up already but all in all this fish is not cheap you want to give it the best care you can. Some say they grow slow and some say they grow fast. One should be able to be okay in that tank for about 6months. But then again how big is the fish already? Mine is growing fast in my opinion...about 1.3-1.5" in a month.
planetcatfish.com is an awsome site for big and small cat inquries...about 2' is the biggest i have seen not including the tail streamers...they generally start at around $200 for a 4" cat...if you like the look, but lake the cash the jurunese cat is an awsome fish aswell that is often over looked...same max size as the tigrinus, but might get 30"...
these fish grow kinda big for that kind of tank and itd be ok with other cats except that Tigs can get kind of pricy so you may not feel the want to get rid of it and it may not be as happy being stuck in that tank
Dude, I'm not talking Pseudoplatystoma sp. I'm talking M. tigrinus, I have seen three footers plus and heard stories of 4 footers, nobody ever holds onto em long enough for them to reach their full potential because they sell them off or they die. Oldest one in hobby is maybe 4-6 years old, still a youngin'.