Gold fish was originally a mutant descendant of wild crucian carp. The body color of wild crucian carp is silver-gray, the back is darker, and the ventral surface is lighter. This is a protective color. Therefore, whether viewed from above or below, the protective color of crucian carp makes it easy to mix with the natural environment and can easily avoid water birds. or the predation of carnivorous fish. The body of the wild kingfish is spindle-shaped, and the streamlined sides greatly reduce the resistance, allowing it to move quickly in the water. However, after artificial breeding and evolution, the goldfish I saw today swim slowly, which is purely for viewing and entertainment value. Below, petnet will introduce it to you in detail.

First, the head

The head of the goldfish is small, without scales, and has a pair of eyes without eyelid. There are a pair of nostrils on the upper part of the mouth, the mouth is at the end, and there are no tentacles at the corners of the mouth. Goldfish do not have teeth in their mouths, but they have throat teeth on their throats, which line up to grind food. The gills on the side of the head are used for breathing, and the gills are protected by a strontium cap composed of multiple hard bones. Goldfish rely on dissolved oxygen in the water to maintain breathing, so the water flow must pass through the fish strontium for gas exchange. When inhaling, the mouth opens, water flows into the mouth, and gas exchange occurs between the water and the microfilament blood vessels in the strontium part. The blood in the microfilament blood vessels absorbs the oxygen in the water and releases the dioxide into the water. After the water flows into the mouth, the mouth closes, the strontium flap opens, and the water flows through the strontium wire and leaves the fish.

Second, scales

Goldfish have round scales, and the rear ends of the front scales cover the back scales like tiles front end. Scales streamline the body and protect the skin. There are glands in the skin that secrete mucus to protect the body from bacterial infection and reduce friction. Newborn goldfish do not have scales, and scales do not begin to grow until about a month after hatching, and when scales fall off, they are replaced by new scales. When a goldfish grows, growth rings are formed on the scales, so by observing the distribution and number of growth rings on the fish scales, the age of the goldfish can be inferred. To infer the age of a goldfish, you need to use forceps to remove the scales from the fish and observe them under a microscope.

Three. Lateral line

There is a lateral line on each side of the fish body, extending from the rear edge of the operculum to the caudal peduncle, A tubular sensory organ containing sensory cells with many pores leading out of the body. The lateral line is responsible for detecting the magnitude of the shocks in the water in order to respond appropriately. The sensitivity of the lateral line is very high, and goldfish can also detect slight vibrations in the water. The scales covering the lateral line are called lateral line scales, and each lateral line scale has a fine hole, which enables the lateral line to communicate with the outside world. The number of lateral line scales is very important in the taxonomy of goldfish, and each species has a different number of lateral line scales

four, fins

The body of the fish has fins. The fins are composed of skin supported by hard bones. They are divided into two categories:

Central fins

It grows in the central part of the fish, including the dorsal fin on the back, the caudal fin behind the tail, and the anal fin behind the anus on the abdomen. The dorsal fin has a distinct long spine, the anal fin has a shorter spine, and the posterior edges of both are serrated.

even fins

opposite, there are only two types, namely the pectoral fins behind the operculum and the pelvic fins on the abdomen. In a broad sense, the function of fins is an organ for swimming and balance; if interpreted in a narrow sense, the uses of various fins are different. For example, the role of the central fin is to balance the body of the fish and prevent the head and tail from swinging left and right and rolling left and right. Another example is to stretch the pectoral fins and use the resistance of the water to stop the swimming fish. If only one side of the pectoral fin is stretched, after encountering resistance, the fish will change direction and swim to the side that stretches the pectoral fin. The pelvic fins can also control the body of the fish like the pectoral fins and stop moving. The pectoral and pelvic fins can prevent the head and tail from stopping up and down and stabilize the fish. If you change the angle of the pectoral fins and the horizontal line, you can float and sink. The caudal fin of a goldfish is the main propulsion organ, allowing it to move forward calmly. There are symmetrical muscles arranged on both sides of the spine, the muscles on one side contract and the muscles on the other side stretch, so that the fish body can swing smoothly and the power to move forward occurs.

V. swim bladder

The swim bladder of goldfish is surrounded by many microfilament blood vessels. The swim bladder is a balloon-shaped organ that is located under the spine and above the intestines, and is used for floating and sinking. When floating, the air dissolved in the blood will infiltrate into the swim bladder to form gas. Therefore, the specific gravity of the fish body is smaller than that of water, and the fish will float; increase, so it sinks. These two processes are controlled by the fish's nervous system