Theres a picture of a 30 something inch GATF in the characin media lounge... Personally I wouldn't mix them even though ironically the 30 incher is in with a gator gar in a 900 gallon I believe. You'd have to grow them out separately for sure and then make sure the tiger fish is bigger then the gar. The tank would have to be big enough also for the tiger fish to be able to to swim normally which for a tiger fish is erratically fast and perilous which are all things gars hate, and the gar would have to have enough room to chill out away from its constant crazed movement especially during feeding...However if the GATF is a fin nipper like some/most of them are, your just about screwed. It would be a very tough thing to do without purposely overcrowding an enormous tank which would need enormous filtration. Not to mention how drastically different the growth rates are. Good luck though man, if you do succeed with this it'll be a real amazing tank to see, I hope you do, good luck.