What kind of fish is this?

Black Mary fish (your fish is called swallowtail black Mary fish), and black Mary is also known as the black Molly family. It is easy to raise and docile. It belongs to pelagic fish, and it can also filter impurities and ink marks on the water surface, and it can also ward off evil spirits in the wind. Very suitable for keeping a few in a small tropical fish tank.

Black Mary fish is viviparous, that is, raw fish can swim for their lives as soon as they come out to prevent being eaten by mother fish or other fish.

Black Mary fish is not strict about water quality, and likes water with trace salt. The suitable water temperature is 20℃ ~ 24℃. If the temperature is low for a long time, it is easy to get sick. For example, when the water temperature is lower than 18℃, it is easy to get water mold. Eating miscellaneous food can scrape off algae and aquatic plants on the aquarium wall, so it has the reputation of "cleaner" of aquarium. Mild temperament, easy to mix. Because black Mary fish likes weak alkaline hard water, it is not suitable to be mixed with aliphatic tropical fish. Young fish can be fed with fresh bait, such as small fleas. Sexual maturity is 5 months and the reproductive cycle is about 35 days. [ 1]?