Adequate space would be about 7-10 gallons of water per angelfish. Sometimes, though, even with the best care and the right amount of space, certain strains of angelfish might take longer to mature.
These tubes are very small, so you will need to look closely to notice them. Catching the fish in a net or putting them in a smaller tank temporarily for observation purposes might help you get a better look, just make sure you handle the fish carefully.
If you happen to have another breeding pair, you can put the angelfish you want to sex in with them. This might encourage them to drop their tubes for you to be able to tell their sex.
This isn’t a sure-fire way to tell the difference between the sexes. In some strains of angelfish, this physical difference might not always be present.
On female angelfish, the line from their dorsal fin to their eyes also tends to be a bit straighter than that of the male’s.
Observe these behaviors carefully, though—sometimes fish of the same sex will try to spawn, unsuccessfully of course. Sometimes spawning pairs of angelfish will “kiss” or lock lips. Sometimes this lip locking can be quick and cute, or even a little aggressive, with the fish chasing one another around the tank. [7] X Research source
You may actually observe a female angelfish laying her eggs with careful observation. Keep in mind, though, that even some of the most experienced angelfish breeders and keepers have trouble distinguishing between the sexes.
