The relationship between the daily average temperature change and breeding of Chinese river crabs was sorted out through the daily average temperature change of Chinese river crab cultured in the pond of Xinghua area. It was found that the temperature change between the four crusts and the five crusts had a greater impact on it, and the corresponding treatment of the pond was made in advance for the change of temperature, and the effective measures could be taken to alleviate its impact after the temperature change.
The Chinese river crab (Eriocheir sinensis) is commonly known as the Chinese river crab. In 2019, the national output of Chinese river crab was 778,000 tons. In recent years, the level of Chinese river crab breeding technology has been improved, and the breeding output has gradually increased to about 300 kg /mu, and the output of farmers with high breeding level can reach 400-500 kg/mu. Molting is an important physiological phenomenon of Chinese river crabs. After hatching, the larvae of the Chinese river crab in the Yangtze River system need to undergo a total of 21 molting hulls in their lifetime, including 5 molting at the nursery stage, 11 molting shells in the crab breeding stage, and 5 molting in the adult crab breeding stage. In the process of adult crab farming, there are more problems and greater impacts at the stage of four-shell and five-shell molting, which will determine the efficiency of breeding in this season.
Chinese river crab molts four and five shells, generally in July four shells, August molt five shells. During these two hulls, farmers have taken many measures to improve the success rate of molting, increasing the amount of water exchanged at high temperatures, filling well water, opening aerators, increasing the configuration of oxygenators, and even so, there is always a unsatisfactory place in annual breeding. Sort out some relationships between temperature changes and aquaculture in Xinghua area in the past three years, and provide some new ideas for aquaculture practitioners.
First, the chinese river crab is the most suitable growth temperature
The suitable growth temperature of Chinese river crab is 22-30 degrees. When the ambient temperature of its survival is higher than 30 degrees, it will have an impact on its growth rate, and the high temperature will be accompanied by a serious excess of the pH value, and the pH value will usually reach more than 10, which will have a huge impact on the gills and liver and pancreas of the Chinese river crab. When the temperature of the water body is higher than 33 degrees, the growth and feeding of Chinese river crabs basically show stagnation, and prolonged in the environment with high water temperature will weaken the constitution of Chinese river crabs, which may lead to disease outbreaks and increase mortality.
High temperature and breeding in Xinghua area in 2002 and 3 years
We count that the overall breeding of Chinese river crabs in 2019 is 8-90% profitable, and only 4-5% profitable in 2020. The most important four-hulled and five-shelled Chinese river crabs are basically between July and September. During this period, the cultivation is most prone to problems such as dead grass, low oxygen and high pH.
July to September entered the high temperature period, the average daily temperature in July 2020 was higher than 30 degrees for 1 day, the daily average temperature in July 2019 was higher than 30 degrees for 11 days, and the average daily temperature in July 2021 was higher than 30 degrees for 6 days. Meanwhile, there were 16 days of southerly winds in July 2020, 25 days in 2019 and 20 days in 2021 (see Table 1). It also means that the less weather appears in the south wind, the fewer the number of high temperature days, and the rainy days continue to be more, which means that it is easy to be low oxygen for breeding, and the larger loss of Chinese river crabs in 2020 has a great relationship with low dissolved oxygen.
<col>
month
category
2019
2020
2021
7
The number of days that the south wind appears
25
16
20
The number of days when the average daily temperature is higher than 30 degrees
11
1
6
8
14
4
■ List of climate and high temperature days in July and August in three years (Table 1)
According to the statistics of 40 ponds in Taizhou in 2019 and 2020 for two consecutive years, according to the daily average, the dissolved oxygen in 2020 was lower than in July (see Figure 1), the number of southwinds in July 2019 was 9 days more than in July 2020, and the high temperature of more than 30 degrees in July 2020 was only 1 day. Rainy rain, low temperature, low oxygen, and molting have a great influence on the growth of Chinese river crabs.
■ Average dissolved oxygen of aquaculture water in Taizhou from July to August 2020-2019 (Figure 1)
Between July and September 2021, the average daily temperature is higher than 30 degrees for 6 days, but there are 20 days in the south wind day in July, and the situation of low oxygen has improved greatly compared with 2020, and through online monitoring facilities, it has also been found that low oxygen in 2021 is 1mg/L higher than in 2020 (which may also be related to increasing the configuration of the aerator).
Third, the optimal temperature and breeding
The optimal growth temperature of Chinese river crab is between 22-30 °C, and the cumulative temperature of the average daily temperature in April-August of 2019, 2020 and 2021 in this range is found that the optimal accumulated temperature in 2021 reached 2448 °C on August 26, 2020 at the same time 2137.5 °C in 2020, and 2061.5 °C in 2019 (see Table 2). It is speculated that the overall size of the Chinese river crab will be large in 2021. The effective accumulation temperature is high, the growth rate of Chinese river crab is fast, the resistance of the body needs to be strengthened, and the body will be more sensitive to the stimulation of the external environment, especially in the case of less south wind in August 2021, changes in the water environment will affect the Chinese river crab. Nutritional supplementation in the culture process becomes a limiting factor.
2021（℃）
2020（℃）
2019（℃）
714.5
344
608
684.5
701
515
713.5
657.5
675.5
5
335.5
409
263
26
Product mild
2448
2137.5
2061.5
■ The accumulated temperature of the average daily temperature in three years is between 22-30 (Table 2)
Fourth, the impact of high temperature on aquaculture in 2021
From July 10 to July 16, 2021, there was a daily average temperature of more than 30 degrees for 7 consecutive days, which was the highest temperature between 2014 and 2021 (see Figures 2 and 3). The second 10 days of July coincide with the critical stage of the four-shell molting of Chinese river crabs, which will be a great test for Chinese river crabs (22-30 °C accumulation temperature and 2448 degrees) that grow faster in the suitable range. High temperature is accompanied by high pH, at this time, a part of the Chinese river crab will be affected, the body's immunity will be reduced, the recovery after molting will slow down, and the phenomenon of intermittent death will occur.
(Looking back at the overall farming situation of these eight years, there was a deflation disease in 2014, and this year continued to be low in August (see Figure 3).) In 2015 and 2016, the water trap appeared and continued to be affected by the water stammer. In 2017, there was an ultra-high temperature that lasted for 35 days in July and August, and the maximum temperature in July reached 38-39 degrees Celsius and lasted for 6 days (see Table 3), which was the largest loss of Chinese river crab in 8 years. In 2018 and 2019, the overall breeding production specifications were higher, and the overall incidence rate was not high, and the benefit was better. The phenomenon of water deflation rarely occurs, and some breeding experts have analyzed that it may be affected by the high temperature of 2017, and the crab species have been reshuffled. In July 2020, the precipitation continued, and the Chinese river crab was also larger in size, due to severe losses due to low oxygen). At present, the specifications should have an advantage over 2020, but there is still the problem of low oxygen.
date
Maximum temperature
Minimum temperature
average
Weather
Wind
2017-07-21 Friday
38
29
33.5
clear
South wind 3-4
2017-07-22 Saturday
Southwest winds are 3-4
2017-07-23 Sun
39
34
2017-07-24 Monday
2017-07-25 Tue
Northeast winds 3-4
2017-07-26 Wednesday
28
33
Dongfeng class 3-4
■ Data table of the maximum temperature in Xinghua area in 2020 above 38 degrees (Table 3)
After the four-shell in 2021, it began to enter rainy days, the requirements for pond management increased, and there are currently more soft-shell crabs, and it is not easy to cure. Rainy days, rotten grass, low oxygen. After the autumn, the temperature difference between morning and evening becomes larger, the surface water temperature decreases, and the convection up and down the water body also occurs from time to time, and the pressure of the Chinese river crab is further enhanced.
■ 8-year-old July daily average temperature trend chart (Figure 2)
After entering August, the temperature trend in 2021 is similar to that in 2019, the temperature is slowly decreasing, the overall situation is relatively stable, the most important thing at this time is dissolved oxygen and the body's energy and protein supplementation, whether the nutrition is sufficient will determine the quality and market time of Chinese river crab. The fast-growing Chinese river crab is more sensitive to external stimuli, and it must be paid attention to maintaining the continuous stability of the water environment.
■ Daily average temperature trend chart for August in 2018 (Figure 3)
V. Suggestions for the management of the late stage of Chinese river crab breeding in 2021
1. Morning market and improve quality
The morning market and high quality are very advantageous to the price of Chinese river crabs, And the price of more than 175 grams of male crabs in Figure 4 is counted from 2013 to 2020, and it is found that the price before September 22 every day is the highest in the year (the data comes from the transaction price on the Xinghua area network).
For the Chinese river crab with relatively fast growth rate in 2021, supplementing sufficient and high protein and energy baits such as the special functional materials for Chinese river crabs will not only help chinese river crabs to be listed in advance, improve quality and improve efficiency, but also help reduce diseases in the later stage.
■ 8 years 175g or more of crab prices (Figure 4)
2. Replenish sufficient minerals
Replenishing with sufficient minerals will help the Carapace of Chinese River Crab to be healthy, gain weight, and restore aquatic plants. Through the monitoring of the total alkalinity, calcium and magnesium ions in the ponds of the main breeding areas in the country, it is found that the total alkalinity and minerals in the water body are at a low level in August every year (see Figure 5), which is not conducive to the stability of the water environment. Chinese river crab needs to absorb minerals from the water body, supplement sufficient minerals, help Chinese river crab molt after molting, is conducive to the stability of aquatic plants and algae.
■ Trend chart of pond data change from March to August (Figure 5)
3. Enhance dissolved oxygen
In the late stage of breeding, the situation of water weed reduction is very common, when the constitution and immunity of Chinese river crab are low, the toxins caused by low dissolved oxygen and rotten grass will be more likely to make Chinese river crab soft shell, poisoning, death and so on. By adding sufficient aerators, fertilizer and water to cultivate algae and grass, the dissolved oxygen of the water body can be improved as much as possible, providing a high-quality environment for the digestion and absorption of nutrients for the Chinese river crab.
bibliography:
1. Yang Yong. The harm of high temperature on the cultivation of Chinese river crab and its control[J]Farming and Feed, 2020(3):52-54.