What's the name of this little black fish?

Moon fish? This is an important tropical fish. It is as small as guppies, colorful and attractive. Moonlight fish is 4~6 cm long and has strong adaptability and reproductive ability. Its characteristic is that it can cross with swordfish and breed new varieties. Common moonlight fish species are: red moonlight fish, blue moonlight fish, red-finned golden moonlight fish, golden-headed moonlight fish, double-finned moonlight fish, sail-finned moonlight fish, golden-headed sail-finned moonlight fish and so on.