◎Intern reporter Li Zhaoyu

  Recently, many hairy crabs have been caught and listed one after another. Before the National Day, there will be a peak in bookings. The diners who have been waiting for many days sighed that "I finally waited for you".

Previously, due to the continuous high temperature weather, the listing of hairy crabs in some major producing areas such as Yangcheng Lake and Taihu Lake was postponed.

  So, how does hot weather delay the growth and development of hairy crabs?

Are other aquatic organisms also subject to "roasting" tests?

In this regard, a reporter from Science and Technology Daily interviewed relevant experts.

  Hairy crabs lose their appetite due to heat, and it is difficult to gain weight

  Xu Gangchun, deputy director and researcher of the Freshwater Fisheries Research Center of the Chinese Academy of Fishery Sciences, said: "This year's high temperature weather has had an impact on hairy crabs. Specifically, it is mainly reflected in three aspects: late sexual maturity, slow growth and development, and delayed molting. ."

  Hairy crab, scientific name Chinese mitten crab, is a kind of economic crab widely distributed in my country, also known as river crab and hairy crab.

Hairy crabs generally begin to mature rapidly in late September each year.

The delicious crab paste and crab roe in people's mouth actually refer to the accessory gonads and their secretions of male crabs and the ovaries and digestive glands of female crabs respectively.

Crab paste and crab roe both require hairy crabs to mature before they are suitable for consumption.

"Affected by high temperature, the sexual maturity of hairy crabs is relatively late this year, which largely hinders their timely listing." Xu Gangchun pointed out.

  It is reported that the most suitable temperature for the growth of hairy crabs is 18 to 25 degrees Celsius.

When the temperature is higher than 25 degrees Celsius, the physique of hairy crabs will decline, and their appetite will gradually decrease.

"Generally speaking, when the temperature reaches 30 degrees Celsius, the food intake of hairy crabs will decrease; once the temperature exceeds 35 degrees Celsius, the hairy crabs will stop eating." Xu Gangchun said.

This summer, the temperature in some hairy crab breeding areas in my country is even approaching 40 degrees Celsius, and the hairy crabs are so hot that they don't think about it, and naturally it is difficult to gain weight.

  In addition, the reduced feeding of hairy crabs can trigger a chain reaction of delayed molting.

"Hairy crabs need multiple molts to develop and mature. Once the molting is delayed, its growth period will be extended accordingly." Xu Gangchun said.

  "Although the autumn wind has started, the temperature is not as high as before, but this year's large-scale listing of hairy crabs may still have to wait until October. And everyone must be mentally prepared. Affected by the high temperature, this year's hairy crabs are likely to be smaller than in previous years. Some." Xu Gangchun predicted.

  Aquatic plants hold up "parasols" for aquatic animals

  "In addition to hairy crabs, high temperature will also affect other aquatic products. For example, kelp, sea cucumbers, freshwater fish, etc. that people often eat will grow slowly and even die under the influence of high temperature." Xu Gangchun said, "Affected by high temperature In recent years, cases of aquaculture production reduction or even no harvest are not uncommon."

  Temperature is one of the important factors affecting the content of dissolved oxygen in water, and dissolved oxygen is a necessity for the survival of organisms in water.

High temperature will reduce the dissolved oxygen content in water, leading to suffocation and death of many aquatic organisms including fish and shellfish, resulting in serious economic losses.

  High temperatures also increase water evaporation, leading to increased salinity in rivers, lakes, and seawater.

Once the salinity in the water exceeds what aquatic organisms can handle, they can become sick or even die.

  High temperature will also accelerate the reproduction of various pathogens, and will also reduce the immunity of aquatic organisms, endangering the safety of aquatic organisms.

  "High temperature weather is a problem that contemporary aquaculture must face." Xu Gangchun further said, "At present, methods such as planting aquatic plants are commonly used in aquaculture to deal with high temperature, and they provide a 'parasol' for aquaculture. "

  Aquatic plants can be described as "artifacts" against high temperature. On the one hand, they provide more abundant dissolved oxygen in water for aquatic organisms through photosynthesis, and on the other hand, they can shade aquatic organisms.

"Generally speaking, aquaculture ponds that raise aquatic organisms such as hairy crabs, due to their shallow water depth, usually plant bottom aquatic plants in them; and aquaculture ponds that raise aquatic organisms such as fish, due to their deep water depth, usually plant in them. Plant floating water plants such as hollow lotus seed grass and water spinach." Xu Gangchun said.