They'll breed by 4-5" if they have anything to say about it, lol. When I had my first jag, it averaged 1-1.25" a month but that was because I was doing 50% water changes about twice a day and fed it guppies and worms on top of the basic pellets that he was getting. Got him as a 1" fish and the boss of his brood and grew him out to 6" sl in 4 months before I had to give him away to a friend with a bigger tank. I was growing him out in a 10 gallon, thus the major water changes.
Funny thing is, when I finally got a bigger tank, 55 gallons, including an outdoor summer pond, I got another jag. The second one, despite having more space and with me having more experienced, grew only .5-.75" a month. He was killed by another fish while they were in the pond despite it being over 1k gallons.
