Why did you cut the cadual fin? Torn fins will heal, but if you cut the fin, the regenerated fin rays will never be the same as the original and often times will grow back unevenly.
the longest longnose i have kept was probably around 18" long...maybe a bit larger. it was kept in general isolation while i had it and released back into our research area. i raised it from about 2.5" all the way up to ~18". they grow extremely fast in their first year. the quickest i have grown one up was from 3" to 10" in 21 days.
all but the longnose in the headshot image i posted were wild caught as they are quite plentiful in our research area. these two little ones will hopefully be powerfed and released into a private pond to help control some centrarchids