Sure you can tell the sex. Easy Peezy. Easiest was is to see if it has white spots on its gills like little white heads. If so, these are breeding tubercles which indicate it’s a male and ready to breed. If I can get a clear side view of the anal vent I can tell you too. A male is concave and a female has a little “v” shaped vent. Male also has a dark line running down it. The female also has the line but also has a line crossing it like a “T”. When they start breeding, the male will be the one chasing the female and bumping her. Good luck!