Look at the mouth. Observe the position of the tropical fish's mouth compared to the centerline of the fish.

1. If the mouth is above the center line of the body, such as guppies, swordtails, and Mary fish, you can see by observation that the mouths of these fish are above the center line. We can see that these fish live in the upper waters, so they can tolerate lower dissolved oxygen and belong to hypoxia-tolerant fish.

2. If the mouth is below the center line of the body, such as sucker fish, rainbow fish, anti-swimming cat, Qingtai mouse, seven-star knife, etc., the mouth of these fish is below the center line. We can speculate that these fish live in the bottom of the water and are generally more active at night, so they need higher dissolved oxygen.

Check your posture. By observing the posture of the fish, you can get a general understanding of the living habits of this fish.

Long-shaped fish, such as pencil fish, large pencil fish, dinosaurs, etc. These fish are fast-moving and require a larger body of rearing water, and shallow water in a long tank is better. Flat shape, such as multicolored fairy, colorful fairy, golden pineapple, silver drum; these kinds of fish are often not very active, do not need large water bodies, like quiet, need large tanks of deep water, and small water circulation can meet its needs . Flat and round, such as black skirt fish; this type of fish is more lively and active. Club type, such as map fish and crown fish; this type of fish is larger and more ferocious, and generally requires a larger aquarium to raise. Bar fish such as guppy, zebrafish, black mary. Most of them are small fish, which can be mixed with fish of similar size, and need a wide water surface for their activities on the water surface.