Thats very interesting.. the slowest I ever had a TSN grow was about 1.5" a month but it was already 12" long. Whatre you feeding yours? I power feed them high protein foodIn my experience, don't expect anything like the growth rate of an Achara. If you had this fish in a tank full of guppies (which I do not condone) you could expect maybe 1" per month, however that's when he can eat till he's full whenever he wants. More likely to be 1 /2 to 3/4" per month under a usual feeding regime and good water quality.
Very true tsn genes go down every year in the farmed hobby. Couldn’t say it better myself tho about setting the tone for the fishes life during the first foot or soAt that size they were on bloodworm and high protein sturgeon pellets.
The biggest issue we face nowadays is poor genes as Victor mentioned above and getting them from 3" to 12" is the hardest part until you try to get from 24" + (if they live that long!)
Just remember that whatever you do 3" to 12" is the basis for how they develop, so space and good water are as essential as good food.