Key Technical Points for Overwintering Management in Enclosed-Ravine Rana chensinensis Farming

    Rana chensinensis has the habit of hibernating underwater for the winter. From late September each year to mid-to-late April of the following year, a period of up to 6 months, overwintering management in artificial enclosed-ravine frog farming means, according to the living characteristics and needs of Rana chensinensis during this period, artificially selecting and creating suitable overwintering sites and water environments to ensure their safe overwintering.

    I. Constructing Overwintering Ponds

    Overwintering ponds, also called hibernation ponds, are places where Rana chensinensis gathers to hibernate. Some natural pools, deep pools in mountain streams, or reservoirs with good conditions within the frog farm can be used as natural overwintering ponds for Rana chensinensis, but most frog farms need to construct overwintering ponds artificially.

    1. Site selection: Choose a location at or near the place where Rana chensinensis gathers and descends the mountain in autumn, select the side of a river channel (stream), keep 5-10 m away from the river channel, and choose flat terrain with clayey soil as the site for constructing the overwintering pond.

    2. Specifications and number of overwintering ponds. When constructing overwintering ponds, the pond depth is required to be 3-4 m, the water depth 2-2.5 m, the pond bottom flat, and the surrounding slopes at 70-80 degrees to prevent collapse after water immersion. If the pond bottom is sandy and loose, it must be padded solid with clay to prevent seepage. The area and number of overwintering ponds are determined according to the terrain conditions of the frog farm and the number of frogs overwintering in normal years. Where the terrain is flat and open, large overwintering ponds can be constructed, with a single pond area of 800-1,000 sq m; where terrain conditions are poor, small and medium-sized overwintering ponds can be constructed, with a single pond area of 200-300 sq m. The number of overwintering ponds is determined as appropriate according to the amount of overwintering frogs raised in normal years; generally, the overwintering density of adult breeding frogs is 80-100 per sq m, and that of young frogs is 200-300 per sq m. One frog farm constructing 3-4 small and medium-sized overwintering ponds can provide overwintering for 20,000-30,000 breeding frogs and 150,000-300,000 young frogs. When constructing multiple overwintering ponds, the spacing between them must reach 500-1,000 m, and each pond must have separate irrigation and drainage.

    II. Preparation Before Use of Overwintering Ponds

    Overwintering ponds that have been used in cycles for many years have relatively thick silt at the bottom, which affects water storage capacity and accumulates large amounts of pathogenic bacteria and natural enemy pests of Rana chensinensis; therefore, careful repair and treatment must be carried out before the overwintering period arrives.

    1. Silt removal: Release the pond water and remove the silt at the pond bottom, restoring it to the original bottom layer of the pond.

⟧    2. Bottom drying: After removing the silt, control water intake and let the pond bottom be exposed to sunlight for 20-30 days, which can kill some pathogens and pests.

⟧    3. Pest killing and sterilization: 20-30 days before filling with water, spread quicklime on the pond bottom and surrounding pond walls for disinfection. This method can effectively kill pathogenic bacteria of Rana chensinensis and natural enemy pests such as leeches and parasites.

⟧    4. Laying hiding materials: Before filling with water, first lay a layer of broadleaf tree leaves about 5 cm thick on the pond bottom, or grass bundles tied from gramineous weeds, then cover them lightly with crushed stone and mud or sand. These hiding materials help Rana chensinensis lurk underwater for hibernation.

⟧    5. Filling with water: In late October, before Rana chensinensis enters the overwintering pond to hibernate, fill the pond with water to a depth of 2.5 m and keep it clean.

⟧    III. Overwintering Management

⟧    In mid-September, when the air temperature drops below 10°C, Rana chensinensis begins to migrate toward water sources at the foot of the mountain. It first enters shallow water areas and lurks there. From early November to mid-November, when the air temperature drops below 5°C, Rana chensinensis enters deep water areas to hibernate, until the end of March to early April of the following year.

⟧    1. Management during the scattered hibernation period: Mid-September to early November, 45-50 days. The characteristic of this period is that most Rana chensinensis lurk separately and scattered in shallow water areas, in an unstable hibernation state, and can still move on land at night. The management focus of this period is: separate the captured Rana chensinensis into commercial frogs, breeding frogs, and one-year-old young frogs; send breeding frogs and young frogs to storage ponds respectively. The water depth of storage ponds is 40-80 cm, and the storage density is 500-800 per sq m of water surface. Storage ponds can also use incubation ponds and tadpole rearing ponds. If the river water within the frog farm is sufficient, overwintering ponds can also be temporarily used instead, that is, keep the water depth of the overwintering pond at 50-80 cm. Put in the overwintering frogs, and before Rana chensinensis enters hibernation in early November, replenish the overwintering pond water in time to a depth of 2-2.5 m. The surroundings of the storage pond must be enclosed with plastic sheeting to form a fence 50-60 cm high, with the bottom compacted with tools to prevent Rana chensinensis from escaping. Because Rana chensinensis gathers and lurks in shallow water areas, management and protection must prevent human theft and predation harm from various carnivorous animals.

⟧    2. Management during the concentrated hibernation period: Early November to the end of March of the following year. The characteristic of this period is that Rana chensinensis gathers in deep water areas, crowding together, neither eating nor moving, in a deep hibernation state. The key management points of this period are: