Fish don't have eyelids, so they don't blink. The purpose of blinking is to wet the eyeball, fish themselves live in the water, do not need to wet the eyeball, so they will not blink. But cartilaginous sharks have nictitating membranes, or nictitating folds, which resemble eyelids and protect the eyes, which are usually closed when sharks hunt.
1. Morphology: There are many kinds of fish, and there are roughly four kinds of body shapes. The first is the spindle shape, which is the most common shape, especially suitable for swimming in the water. The second type is flat, such as rays, rays and so on, the body is relatively flat, mostly inhabiting the bottom of the water. The third is the stick type, common eels and eels, good at drilling mud. The fourth is the lateral flat type, such as silver pomfret.
2. Fins: Fish have fins, which help them swim better. Fins are divided into pectoral, pelvic, anal, caudal and dorsal fins, some fish have a pair of pectoral and pelvic fins, similar to the limbs of land animals, others have only one, some fish also have special fat fins. In addition, some fish do not have fins.
3. Fish scales: Most fish have fish scales, which are a layer of protection for fish. They can prevent microorganisms in the water from invading the body, and are of great help in resisting diseases. In addition, scales can reduce the resistance of the fish when swimming, so it can swim faster.
4. Habits: Fish live in the water and need to breathe with gills. Some of them also have auxiliary breathing methods, such as breathing with intestines, skin and mouth. Most of the fish live in fresh water or sea water, but some will migrate back and forth, with migratory spawning characteristics.
