they grow very slow. dont know where you got they grow fast at.. 2nd, at most in a 142 gallon i would do is 6 MAYBE 7. 1 male 5 or 6 females, but juvies you could do 12 tell they get to about the 6 inch mark then start thinning them down. with 12 juvies, you got about 10 months for tell you need to thin down the herd.