a: only during spawning-time they can be vented; and then it's quite visible from the side; the female has a stump protrusion right in front of the anal fin.
after spawnings and between them: impossible!
example: I got a breeding pair, but the
only way for me to tell male from female is
to catch them and view from above in a white bucket.....even then it is NOT easy.
b: No. I can be short about this: it doesn't work. At one time I had 6, 3 males, 3 females; 1 pair formed, but the other four sometimes paired up, sometimes just fought (especially the bigger males), but no spawnings ever happened.
get a group, set up a nice breeding tank, feed small fish and keep the spawning pair (feeding live fish is a trigger for spawning), and put the rest in the showtanks or trade them.
Apart from bulk/size etc the best way to separate the sexes is looking at the head from above; otherwise you can pick up a big male and a small male.
even when sized similar (my breeding pair are equal in length
), the male has a broad snout, the female a more tapering one; the whole head of the male is bigger.
The belly of the male doesn't "stick out" as much, esp when near spawning.
to make a crude comparison:
-males look like very long thin triangles; the widest point is the head
-females look like extremely elongated teardrops; the widest point is the belly