While Len is erring on the side of caution, and is certainly not incorrect for doing so, you can't generalize too much with this family. A Queen trigger will grow very quickly into a very large, very destructive fish that requires at least a 250 gallon tank to itself. A clown trigger will grown somewhat slower, but eventually still require a large tank (although it's space requirements don't match the Queen) all to itself...you have more time with a clown vs a Queen though. The triggers of the genus Rhinecanthus however grow very slowly, around an inch to an inch and a half a year for a time, then slow down considerably. If you bought a juvenile Huma huma, (Rhinecanthus aculeatus and related species) he could live quite happily in a 55 gallon for quite some time...years usually. They also don't get very large in captivity, a 7" captive raised specimen is probably 8 or 9 years old. You can also keep them with other species, space permitting. B. undulatus is another slower grower, about the same rate as it's cousins in the genus Rhinecanthus. It's destructive tendencies however cannot be overstated, definitely a special needs fish! O. niger is a faster grower that needs a large tank, but can be kept with other species.
If you're thinking of a particular species, drop me a PM and I can give you more particulars.
Cheers
Jim
