When will external gills fall off?

[D12DetroitD12]

Ive had my Delhezi for about 4 months now and hes just about 6 1/2'' now and he still has his external gills. Out of all the bichirs Ive ever had Ive never had one that has kept their external gills till they were 6 1/2''. This doesn't really seem normal but maybe im wrong so does anyone know when they will lose their external gills?

 

[Cholly]

It varies some by species and even individuals but that does seem a bit long.

 

[peewee]

delhezi in particular. their external gills tend to stay quite long.

 

[ancientfins]

what was its size the time you bought it?