Venting and male Mbamba

[Steve]

Okay I need some help. I asked about venting fish a bit ago, and appreciate it advice, but here's what.

I lost my really nice Male Mabamba about a month ago. I still feel bad about losing him because I really liked him I still have 3 Mbamba's in the tank, I "thought" all three were females, but now after venting (for my first time) I "Think" one of the three may be Male.

So my question, if it is Male, that gives me 1 male and 2 females in a 55g...but Blair has a male I would like to take. Would I be okay to add it and have 2 males and two females in my 55? As of now aggression is maybe zeros to 15% at most.

[Steve]

BTW since this is my first time venting. I thought the first time they were both the same. But after looking, the two spots are the same size, but I "think" the one(upper) is a bit different shape. So that means its a male??

[Michael Zebrowski]

I always assume when both openings are the same size, it's female; noticeably different sizes, male.  Not concerned with the shapes, just the relative sizes.