Mark S

Oh, there are so many options! I'll just mention a few I've had success with in that tank size or smaller. Most Corydoras will breed happily in a tank that size. Same for probably just about any Pseudomugil species. I've bred P. furcatus, P. gertrudae, and P. luminatus. I've also bred the dwarf neon rainbow (Melanotaenia praecox) in that tank size. Ricefish haven't been mentioned yet. Just got a beautiful group of platinum Miyuki that are breeding in a 15 gallon. Of course, most "standard" livebearers (guppies, Endlers, platys, mollies). A 20 long has such a great footprint, being long enough for fish to spread out and get away from each other when needed.

I would guess they gave birth and all the babies were eaten. Hard to tell for certain from those photos, but I'd say the females looked pregnant. Four months is plenty of time for them to mature.

I agree, definitely male.

What are your preferred methods for keeping snails at a minimum in your breeding tanks? I've been baiting with green beens or zucchini and removing them, but it is a slow and never ending task.