1. Fish: The fresh fish scales are intact and close to the fish body, not easy to fall off, the mucus is transparent and has no odor, the eyeball is full and transparent, the lid is closed, and the color is bright red. The muscles are strong and elastic, and the fingers are pressed against the muscles without depression. When the fish body is held, the tail does not hang and the anus is closed. When the fish leaves the water, a mucus is secreted from the body surface. After the fish dies, the mucus is first decomposed under the action of bacteria to produce an odor, and then gradually deepens into the body to continue to decompose the tissues, causing the scales to fall off due to decomposition of the tissues around the eyes. The eyeball is sunken, chaotic and dull; the sputum changes from bright red to dark brown, and there is odor; the microbes in the intestine grow and multiply and produce gas, causing the abdomen to swell, the anal canal protrudes from the anus, and when the degree of corruption is severe, the fish is broken, the fish Bone detachment.
2. Shrimp: Fresh shrimp head and tail are intact from the shape, with a certain degree of curvature, and the shrimp body is quite strong. Non-fresh shrimp, the head and tail are easy to fall off, can not maintain its original curvature. From the color, the fresh shrimp skin is bright, green or blue. The non-fresh shrimp shells are dark and change from gray to red or gray-purple. On the flesh, the fresh shrimp is firm and tender, and the flesh is soft when not fresh.
3. Crab: It is better to live, if it is dead, it should not be eaten. The fresh crab legs are firm and fat, with a hard feel by hand, the umbilicus is full, and the weight is heavy. The buckle can be flipped over on the ground. The shell is cyan, bright, and the abdomen is white. The "umbilical cord" has crab yellow and tender meat. The fresh crab legs are loose and thin, the action is not lively, the weight is light, the back shell is dark red, the meat is soft and the taste is not delicious.
Why do some fish or meat shine at night?
In 1985, a family in a city bought two river fish from the market. After removing the internal organs, it was placed in the basin because it was too late to cook. When it came back at night, the fish suddenly saw a light blue light in the dark. I don’t know. What is the reason? Can fish still be eaten?
Why does the fish shine at night? According to the freshness of the fish, there are different types of bacteria on the fish, the most common ones are Pseudomonas, Yellow Bacillus, Alcaligenes, Vibrio albicans, Aeromonas Etc., these bacteria can multiply on the surface of fish at suitable temperatures, some of which can produce yellow-green or blue fluorescence. Fluorescence is a substance that emits light in the dark after exposure to sunlight. Some bacteria can also produce phosphorescence, which can be illuminated in the dark, commonly known as "ghost fire" is phosphorescence. Therefore, the luminescence of the fish is related to the growth and reproduction of these bacteria. It can also be produced under normal conditions, and is not caused by any radioactive substances. Can the radiant fish be eaten? This depends on the extent of the bacteria's pollution and the freshness of the fish. If the fish has been spoiled and deteriorated due to the proliferation of bacteria, it should not be eaten again; if the fish body does not show significant deterioration, then Still edible. But be careful to wash it before cooking.
In addition to fish, meat may also have this luminescence, which is caused by some bacteria that produce fluorescence. These bacteria are non-pathogenic bacteria, generally do not cause human diseases, but only cause animal tissues to produce spoilage and deterioration, so these bacteria are called spoilage bacteria.