1. Guppies: Guppies are common small tropical fish. Its body length is only about 5 cm, but its tail accounts for one third of its whole body. This kind of fish has strong adaptability to the environment, can endure dirty water, has low oxygen consumption and miscellaneous feeding habits, and as a tropical fish, can endure water temperature below 20 ℃.

2. Black Mary: Black Mary is an artificially cultivated ornamental fish with a body length of up to 8 cm. It has lax requirements on water quality and can even live in salty water. It is an omnivorous fish. Because it eats algae, it can also be used as a clean fish. In addition, because it likes weakly alkaline hard water, it cannot be mixed with lipid tropical fish.

3. Red swordfish: Red swordfish is a kind of swordfish, which is completely red, and the tail side of male fish extends out like a sword. Its body is strengthened, easy to raise, not picky about food, can eat earthworms, red worms and artificial feed, and the feeding water temperature should be controlled at about 24 ℃.

The most accurate way to judge an upper fish is to look at the water layer where it lives. If it spends most of its time in the upper layer, it is naturally an upper fish. But if you don't have a chance to observe it like this, you can look at its lips. Usually, the lower lip of the upper fish is longer than the upper lip, while the upper and lower lips of the middle fish are as long, and the mouth of the lower fish grows downward.