Hi:
I'll add to Marys comments......
75 gal minimum and thats pushing it for being too small. I recently got rid of 2 adult volitans which had pec wing spans of over 12". They couldn't even turn around in a 55gal tank. (I have a 180gal)
You can keep a juvenile volitans in a 55gal or less, just remember that these fish reach adult in 1.5yrs, so you have a 15" fish on your hands 1 yr from now.
One problem w/ small tanks and big meat eaters is waste, if you do have a small tank, be anal about water quality. Skimmers, rountine water changes, and good husbandry are key to keeping water quality issues at bay.
Lastly, ween it over to SW based prepared foods ASAP
frank