How to improve the overwintering survival rate of forest frogs? These measures must be mastered

The forest frog, also known as Hasma, is mainly represented in China by the Chinese forest frog (Rana chensinensis) and the Heilongjiang forest frog (R. amurensis), which are widely distributed across the three northeastern provinces of China. Because of the forest frog's unique nutritional and medicinal value, especially its frog oil, it is highly sought after in domestic and international markets, with a huge gap between supply and demand. Zhao Zhenhuan of Shanghai Fisheries University first proposed the idea of relocating Chinese forest frog breeding southward in the 1950s, and conducted growth and reproduction experiments under the natural conditions of the northern suburbs of Shanghai at 31°N latitude and 122°E longitude. Over the years many people have conducted basic research in this area. Wang Shoubing of Fudan University studied the effects of temperature changes on the embryonic development of the Chinese forest frog, and the results showed that the Chinese forest frog has strong tolerance to temperature changes during embryonic development, and spring temperature changes in the south will not seriously affect its embryonic development. Jiang Chaoguang of Fudan University studied the nutritional requirements of the Chinese forest frog during the tadpole stage, and preliminarily determined the feed formula for the tadpole stage of artificial breeding of the Chinese forest frog. The above research results provide a theoretical basis for artificial breeding of the Chinese forest frog in the south.

1. Medicinal value

Hasma oil is the oviduct of the female forest frog and is a precious traditional Chinese medicinal material, especially that of the Chinese forest frog and the Heilongjiang forest frog, which are large in size and high in oil content. The protein content of Hasma oil is 76%, containing more than 20 kinds of amino acids, followed by fat and carbohydrates. It also contains a variety of minerals: calcium 5.75%, phosphorus 0.052%, iron 1.465%, potassium 16.52%, sodium 3.56%; it is rich in vitamins A, B, C and a variety of hormones, and contains 347 kcal/100g of energy. The main active ingredient of Hasma oil is frog alcohol, which has the effect of “tonifying the kidney and replenishing essence, moistening the lung and nourishing yin.” It specifically treats kidney deficiency and weak qi, energy depletion, memory loss, obstetric and postpartum hemorrhage, postpartum lack of milk, and neurasthenia. Chinese traditional medicine believes it can treat “infantile red qi, swollen sores and umbilical injury, pain relief, insufficient qi, removal of fatigue, relief of toxin, diuresis and swelling reduction, consumptive cough,” and has a special effect of nourishing the lung and moistening the kidney.

2. Nutritional value

The forest frog can be considered a delicious delicacy, and is truly an animal resource of high economic value for both medicinal and food use. Its products are extremely popular in international markets, especially enjoying a very high reputation in Hong Kong, China and Southeast Asia, and sell at high prices. It is one of the important commodities among China's exported medicinal animals. The main product of the forest frog is Hasma oil, currently priced at 2000-3000 yuan/kg in the domestic market. The by-products of the forest frog - frog meat and frog roe - are delicacies on the dining table, and its internal organs and bones can be used as feed.

3. Ecological benefits

According to statistics, 1 forest frog can prey on more than 30,000 various pests in 1 year. It specializes in eating moving insects or worms. Through stomach examination, it was found that the food types appearing in the forest frog's stomach reach nearly 60 species across 6 classes and 13 orders, among which the class Insecta is dominant. These are mainly Coleoptera, Orthoptera, Homoptera, Diptera, and Hemiptera, followed by Arachnida, Araneae, and mollusks such as river snails and snails. The forest frog mainly lives under coniferous and broad-leaved mixed forests, and forest pests can satisfy the large amount of food needed for its growth. The forest frog is insatiably greedy and captures almost without selection all insects within its reach, so the forest frog is also known as the famous “forest guardian,” and especially for the control of larch caterpillars in forest areas, it has important ecological significance.

How to improve the overwintering survival rate of forest frogs

Winters in the north are long and cold. Under harsh environmental conditions, the overwintering of the Chinese forest frog in northern mountainous areas mainly occurs in water bodies. During overwintering, the metabolic intensity of the forest frog decreases, the number of respirations decreases, the heart rhythm slows, and blood vessels and microvessels contract and other physiological changes occur, causing the oxygen consumption of the forest frog to decrease month by month, which helps the forest frog survive the severe winter in water. However, there are also many unfavorable factors affecting the safe overwintering of the forest frog. Under long-term ice-sealed conditions, the interior of the water body must undergo changes completely different from those before freezing. As the air temperature drops and the ice layer thickens, the water temperature gradually falls to 0°C; due to freezing and seepage, the amount of water decreases. Due to the decomposition of organic matter and the respiration of frogs, fish and other organisms, the oxygen content in the water continuously declines, while the carbon dioxide content continuously rises. These changes in environmental conditions pose a serious threat to the overwintering of the forest frog. Therefore, efforts must be made to improve the overwintering survival rate of the forest frog.

First, the preparatory work before the forest frog's overwintering must be done well. For example, when newly building overwintering ponds, or using original pond dams and water pits for overwintering, the pond dams should be enlarged and deepened, and silt and weeds should be removed as much as possible to reduce organic oxygen consumption and prevent the occurrence of harmful gases.

Second, the demand of the forest frog for dissolved oxygen during overwintering must be met. There are two sources of dissolved oxygen in water: one is oxygen from the air dissolving into the water, and the other is oxygen produced by photosynthesis of aquatic plants. However, after the water surface is sealed by ice, the contact between water and air is cut off by the ice, oxygen in the air cannot dissolve into the water, and the source of oxygen replenishment from the air is cut off. Many overwintering ponds have no aquatic plants. Even if there are aquatic plants, due to the thick ice layer and dark ice in mountainous areas, the photosynthesis of aquatic plants is directly affected, and it is also unlikely that oxygen will be produced by aquatic plant photosynthesis. Therefore, the main cause of forest frog death during overwintering is death by hypoxia and suffocation.

According to many years of observation, flowing-water overwintering ponds have little problem, because natural flowing water is continuous and dissolved oxygen in the water is replenished in time. Therefore, mass frog deaths will not occur in winter.

At present, most overwintering ponds for frog farming are still-water (also called stagnant-water) overwintering ponds. In winter the water source dries up, and no flowing water passes through the overwintering pond, so dissolved oxygen cannot be replenished, and the decline rate of oxygen content in the water accelerates month by month. By January the oxygen content in the water is only about 4 mg/liter of water (the normal requirement for forest frog overwintering is 6 mg/liter of water). In particular, frogs overwinter at the bottom layer of the water, while oxygen deficiency in pond water often begins from the bottom layer, and the dissolved oxygen content in the water is greater at the top and less at the bottom, posing a very great threat to the frog during overwintering.

To solve the problem of insufficient dissolved oxygen in overwintering ponds, the following three methods can be adopted: First, the water storage capacity of the overwintering pond must be sufficient, and it must be filled with water around the Autumn Equinox, with a water depth not less than 2.5 m. According to the requirement of 150 overwintering frogs per sq m, the water surface area cannot be too small. How large the water surface should be can be estimated based on putting in 1000 egg masses per year and an overwintering pond water surface area of about 1 mu. Second, when frogs and fish overwinter in the same pond, because frogs and fish compete for oxygen, the amount of overwintering fish should be controlled at 0.2 kg per 1 cubic meter of water, half of the normal amount. Wild miscellaneous fish should also be removed as much as possible to reduce oxygen-consuming factors. Third, throughout the overwintering period, careful management is required, and the overwintering condition of the frogs must be observed at regular times. Because aquatic animals are very sensitive to hypoxia, when hypoxia is severe (for example, when dissolved oxygen drops below 3 mg/liter of water), aquatic insects such as cyclops, water boatmen, water scorpions, and aphids can be seen near the ice holes. Therefore, when opening ice holes, observing whether aquatic insects swim upward can serve as an indicator for inferring how much dissolved oxygen is in the water.

In cases of severe hypoxia, the following measures can be taken:

First, add water to supplement oxygen. Draw nearby water sources (well water, river water, reservoir water, spring water) and inject them into the overwintering pond. Second, make ice holes to supplement oxygen. Ice holes should be made in deep water, with one ice hole 1.5 m wide and 3 m long per 1 mu of water surface. Arrange them along the main wind direction, and use the effect of wind to form water waves, accelerating the dissolution of oxygen into the water to improve the oxygen supplementation effect. To prevent the ice holes from freezing again, they can be covered with straw curtains at night.