1. Length and weight
Koi fish has a strong physique, bright colors, changeable patterns and beautiful swimming posture, which is of great ornamental and breeding value. Koi fish is a large individual with a body length of 1- 1.5m and a body weight of 10kg or more.
Koi fish's body length is over 90cm, which can be said to be quite large. However, a koi fish of Pinus densiflora with a body length of 125cm appeared at a Japanese oral judging meeting, and what's more, a super giant carp with a body length of 150cm and a weight of 45kg was recorded.
2. Fins
Fish can be divided into pectoral fin, ventral fin, dorsal fin, anal fin and caudal fin. Fin is the motor organ of koi fish. The pectoral fin and ventral fin are equivalent to human limbs. Fins have the ability to regenerate after being removed or broken.
3. Must
The two pairs of tentacles on koi fish's mouth are sensory organs searching for food in the mud.
4. Eyes
Like most fish, koi fish has no eyelids, so his eyes are always wide open and never closed. At the same time, there are no lacrimal glands and no tears. Koi fish's eyes are located on both sides of his head, so his field of vision is very wide, reaching 160 ~ 170 degrees, twice that of human beings. The iris cannot move, so the pupil cannot be adjusted. So koi fish can't tell small things apart, and he doesn't like strong direct light.
5. Ears
Koi fish has no outer ear, only inner ear, no cochlea. So some people say that fish are deaf. But koi fish's inner ear does hear sounds; At the same time, the swim bladder can also play the role of hearing; But what really plays a hearing role is the lateral lines on both sides of the fish.
6. Mouth
Koi fish has no teeth in his mouth, so he can't chew. But there are a pair of throat teeth in the throat to crush food.
7. Leather color
Koi fish's skin color is very ornamental. All colors in koi fish are the result of the contraction and diffusion of pigment cells buried under the epidermis and between tissues under the scales. This cell contains four pigments: melanin, yellow pigment, red pigment and white pigment. The contraction and diffusion of pigment cells are related to sensory organs and nervous system, and they are particularly sensitive to light, which makes koi fish show dazzling colors and stripes.
8. Skin and dermis
The fish body is an outer skin, which is divided into outer skin and inner dermis. Mucus secreted by epidermal mucus cells can effectively prevent parasites from attaching. Below the epidermis is the dermis, which contains blood vessels and nerves, and the base of the fish scales is buried in the dermis.
9. Scale
Fish are covered with scales, which are differentiated from dermal cells and have protective effects. Once scales fall off, they can regenerate. However, the regenerated scales will be disordered. Fish scales have rings like sawn tree trunks, from which koi fish's age can be calculated.