well if you are just picking up large specimens then you obviously wouldn't need a grow-out tank...all the fishes currently in GD were grown out to that size from YOY status (except the spotted gar, which would have been a year or two when captured in 2008).
unfortunately there is a bit of a choke-point between GD and GDII...the gars get big in GD, but not big enough (in most cases) to withstand the croc II initiation in GDII...so there is somewhat of a stasis at this point (at least for the time being ) --
--solomon