captive bred dels grow a hell of alot faster than wild caught.I had a 4" captive bred catch up to a 9" wild caught in 5 months while the 9" only grew 1" in the same time.
they were both in the same tank. my wild caught laps grew 2" in a year! super slow growers
It depence on the food and the temperature first.
Further on in my opinion they grow if the tank replace some shaddowplaces for our guys and you give them a conditionaly soft stream in the tank.
In my opinion if the stream is too hard and the polys have to swim a lot they put the energy in the swimming instead of the growing