Male jags can get to around 14-16 inches in captivity. Maybe a little more. Females are smaller hitting around 12-14 inches.
A single male jag should be kept in a tank size of around 6ft x 2 x 2 as a bare minimum. Maybe a 5x2x2 if you were to get a female.
I had a male as a juvenile in my 5ft 450 litre (125 US gallons) tank for a while. He was only around 2 inches and lived happily with a 5 inch red devil, 4 inch texas and 2 red jewel cichlids. Then as the jag got bigger his aggression started to show so i had to rehome him. He was around 6-7 inches at this point.
And what i meant was a 6x2x2 would be ok as a minimum for a single male jag for life obviously i would of had to moved my male into a bigger tank as he grew but as mentioned, his aggression got a bit much and i didnt really want to have to get a 6x2x2 or bigger for just 1 fish.... so he had to go
From the LFS. They have a breeding pair for sale and they bred. Since they didn't want to raise them I asked them if i could have a few, so they netted me a few. Just about in time, since the day after the parents ate all the ones that were left.
This is what they look like at the moment