How long did it take to reach his max size ?
Did you find females grew faster than males ?
Your old congi (male) is definitely growing slower than ghost congi
She grew from 18" to 25" in about 1-1.5 years. I had her for awhile when she was smaller til about 14"-15". Sold her and got her back at 18". Total about 3 years for 7"-9" to 25".
My other congicus took a total of 4 years to grow from 18" to 24".
I don't think bichir gender has anything to do with growth rate but definitely female bichirs get more massive from my experience.
I sold one of my friend a 16" Nigerian Lap and possibly half a year later it was 20"-21".
Someone in Japan grew their Congicus from 7" to 24" in one year.
Bichirs growth rate are not linear. It's very random. I've heard they don't stop growing, they are constantly growing. (not sure if its true) but in my experience some just grow REALLY slow compared to others.