I've kept a pair (or say, at least 2 individuals) until they reached 40 cm or so and they really started to get too big for a 2 meter 500 litres tank.
It's a funfish to keep and quite visible as Dorads go if you have the room. I've since seen Pterodoras in captivity wich are quite a bit larger than mine were. so, yes, they really reach impressive sizes in captivity when given enough room.
2 feet and more is possible! according to some sources it should reach 35 cm (wich unfortunately isn't the case), to some others 1 metre; wich I think is likely.
the biggest I've seen myself in a zootank was about 75 cm; that's 30" or 2.5 feet for the non metrics out there. add girth and the spread of those enormous winglike pectorals and you have a real tankbuster on your hands.
from my own experience I reared 1 from a tiny by-catch (2"! tiny) and added another when that one was about 25 cm or so of a similar size.
when they're small they are very nocturnal. the first hint that I got an unusual Dorad was when I noticed crscent-like bites out of plantleaves. there was no fish in that tank that could take such bites. it was about 3" then and slowly switching from omnivore to herbivore.
later it started on any softleafed plants; the Echinodorus were the first to go.
then at 1 time I woke in the morning remembering a field of inedable Cryptocorynes, about a square foot....but they had somehow disappeared in a single night! soon after that the Giant Vallisneria wich were abundant and quite big started to look like they were pruned by Cohen the Barbarian overnight......
Also, very tyupical: this fish REALLY LIKES TO SWIM! it's migratory and it shows. from 8" and up every night it would cruise the tank, with the lights still on. it's got a 'clock' and dusk is obviously the time to roam about and move. wich makes sense for a fish that has the dietary requirements and behaviour of a horse......
it does make sense to move about when the local greenery is razed to sandlevel.
Also when the duo got real big, every fall the swimming habits would get intense; water slopping out of the tank; themselves ramming their noses to the outlet for hours on end during the evening and night and that went on for weeks and weeks.
so when september and october come around it's time to go upstream. it was like having your own armourplated salmon as pets.
they also get quite tame; you can with a bit of patience hanndfeed them, wich is unusual. most Dorads are shy and a bit skitterish. this one really loves to eat, so a bit of cucumber or lettuce can get them feeding from the surface. I tried fruits as well but with little success as I couldn't get Amazonian fruits.
they really like unfrozen peas (the tincan variety is way too slimy and polluting), unfrozen spinache, cucumber, any aquatic plant (and I mean ANY, they even feed on Javafern, wich has the nutricial value of plastic leaves with barb wire rootwork), they love floating plants (duckweed, Floating Lettuce/Pistia), zucchini, you name it.
sand is the best choice of substrate. if you seen em dig and swipe those massive tails....well I got the pebbles in there out real quick, I tell you. I could hear stuff rattle against the glass at night......
and no agressive fish. they go nuts when harassed, torpedoe themselves through the tank at high velocity. gentle tankmates is a good idea.
I never ever saw or experienced them feeding on any tankmates, no matter how small. they are completely harmless!
if I ever win the lottery, get a whoppin' big house and an indoor pool this would be one of the fish in there. well worth keeping IMO.
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