Is a shark a fish or not?

Sharks belong to cartilaginous fish, a subclass of vertebrates, and live in the ocean. A few species enter fresh water, which is a group of medium and large marine fish with fast swimming speed. ?

The endoskeleton of sharks is completely composed of cartilage, which is often calcified, but there is no real bone tissue. The exoskeleton is not developed or degenerated. The body is often covered with skin teeth (thin-walled scales), with various teeth and hard muscles, but the membranous bone never exists and the skull is seamless. The upper forehead is composed of palatal cartilage and the lower forehead is composed of Mayer cartilage.

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The growth habits of sharks

1, growth rate. When food is sufficient and ecological factors such as temperature are suitable, freshwater sharks grow rapidly, and their weight and body length can be multiplied. Growth is mainly affected by temperature, food, age and physiological conditions. The growth law is that the body length of young fish increases rapidly and the weight increases relatively slowly;

When the body length increases to a certain length, the growth rate begins to slow down, while the body weight increases rapidly. The data show that freshwater sharks can generally grow at an average speed of more than15g per day during the suitable growth time from June to June. Freshwater sharks raised for 2 years can grow to more than 2 kilograms.

2. Temperature and growth. The suitable water temperature for growth is 20℃~33℃, and 28℃~30℃ is the most suitable. Therefore, the growing season is from late April to early and middle June 10, and the difference between north and south of China is about 20 days.

3. Bait and growth. In the case of artificial feeding, the quantity and variety of bait will directly affect the growth of freshwater sharks. When the specifications, stocking density and environmental conditions of fish species are similar, whether it is individual growth or population yield, feeding concentrate is better than coarse feed;

Fish meal, silkworm chrysalis powder and other mixed feeds containing certain animal protein grow fastest in concentrated feed. Therefore, it is feasible to cultivate plankton by artificial fertilization in aquaculture to promote its growth.

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