[DJRansome]

Of course there are exceptions because as you state, it depends. If you said auratus the number would be different for example.

Oh and that is for a mixed-gender tank with 1m:4f of four species, no look alikes and no duplicates on genus.

An all-male tank would be different.

 

[DJRansome]

Somewhere between 18-20 seems like a good answer to me. 8)