Dick,
Impoundment Barra growth rates are directly influenced by a number of factors. Without getting too technical,the ones below are just a few.
1. Water temperature.
2. Availabilty of digestable energy
3. Stocking rate.
Once released (@55mm) fish take roughly 12 months to gain an average weight of 2.5kgs and legal size.
From here on in each fish will have individual traits but on average 2.5kg - 3kg body mass per year thereafter.
Some metre class impoundment barra make the magic metre mark at around 4 years old, depending on strain, brood stock quality, availabilty of food and good water temps, 28 degree's being optimum.
Wildfish by comparison are much slower therefore much more valuable in the sustainability stakes.
It can take a wild barramundi 8+ years to reach the meter mark, from memory around 3 years to reach minimum legal size.
Hope this helps.
Cheers
Jas