Iâm gonna guess thatâs the height rather than the length.
A lot of people think they can sex the domestic Angel varieties but they canât, because theyâre hybrids between two species, one that has a concave head and one which has a convex head. This makes the domestic Angel shape quite variable, and the âmale getting a hump on the headâ thing doesnât apply. If you grew a few of either species (wild caught) youâd be able to tell male from female once they started to mature, and if you grew several domestic ones up together the females would usually be fatter in the belly when theyâre mature and growing eggs, but with immature fish you simply canât tell. Even with mature fish itâs just guessing.
The only sure way is to see a femaleâs egg tube fully extended, or eggs, to be sure you have a female, and you can only tell if you have a male if the eggs are fertilised (often two females will âspawnâ together, with one just going through the motions with a breeding tube that looks like a maleâs because it isnât fully extended).