Overwintering Management Techniques for Rana Chensinensis in Enclosed-Gully Farming

Rana chensinensis has the habit of hibernating and overwintering underwater. From late September each year to mid-to-late April of the following year, a period of up to 6 months, the overwintering management of artificially enclosed-gully frog farming consists of selecting and creating suitable overwintering sites and aquatic environments according to the characteristics and needs of Rana chensinensis during this period, so as to ensure their safe overwintering.

I. Construction of Overwintering Ponds

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

1. Site selection: choose a place at or near where Rana chensinensis gathers and descends the mountain in autumn, select a spot beside a river channel (stream), keep 5-10 m away from the river channel, and choose a flat area with clay soil as the site for building the overwintering pond.

2. Specifications and quantity of overwintering ponds: when building 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 a normal year. Where the terrain is flat and open, large overwintering ponds can be built, with a single pond area of 800-1000 sq m; where terrain conditions are poor, small and medium-sized overwintering ponds can be built, with a single pond area of 200-300 sq m. The number of overwintering ponds is determined as appropriate according to the number of overwintering frogs raised in a normal year; generally, the overwintering density is 80-100 adults per sq m for mature breeding frogs and 200-300 per sq m for young frogs. Building 3-4 small and medium-sized overwintering ponds on one frog farm can accommodate 20,000-30,000 breeding frogs and 150,000-300,000 young frogs for overwintering. When building multiple overwintering ponds, the spacing between them should reach 500-1000 m, with separate irrigation and drainage for each.

II. Preparation Before Use of Overwintering Ponds

Overwintering ponds that have been used in cycles for many years have relatively thick sludge 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. Desilting: release the pond water, remove the sludge at the pond bottom, and restore it to the original bottom layer.

2. Sun-drying the bottom: after removing the sludge, control the water inflow and let the pond bottom be exposed to the sun for 20-30 days, which can kill some pathogens and pests.

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

4. Laying concealment 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-sand; these concealment materials help Rana chensinensis lurk and hibernate underwater.

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 temperature drops below 10 degrees C, Rana chensinensis begins to migrate down the mountain to water sources. It first enters shallow-water areas and lurks there; from early November to mid-November, when the temperature drops below 5 degrees 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 dispersed 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 onto land at night. The management focus during this period is: separate the captured Rana chensinensis into commercial frogs, breeding frogs and one-year-old young frogs, and send the 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 hatching ponds and tadpole rearing ponds. If the river water on the frog farm is sufficient, overwintering ponds can also be temporarily used instead, that is, keeping the overwintering pond water depth at 50-80 cm. Put in the overwintering frogs, and before Rana chensinensis enters hibernation in early November, promptly replenish the overwintering pond water to a depth of 2-2.5 m. Around the storage pond, a fence 50-60 cm high should be made with plastic sheeting, with the bottom compacted with labor to prevent Rana chensinensis from escaping. Because Rana chensinensis concentrates 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 concentrates in deep-water areas, crowding together, not eating or moving, in a state of deep hibernation. The key management points during this period are:

(1) Promptly send the overwintering frogs in the storage ponds to the overwintering ponds. The frog stocking density in overwintering ponds is 80-100 per sq m for breeding frogs and 200-300 per sq m for young frogs, maintaining overwintering with flowing water. Winters in Northeast China are cold, and after winter begins many rivers and streams in many farms become frozen and stop flowing; for such overwintering ponds, the overwintering density of Rana chensinensis should be appropriately reduced by half.

(2) During the overwintering period, frequently observe the water flow conditions and keep the water level under the ice no lower than 1.5 m.

(3) After snowfall, promptly clear the accumulated snow on the ice surface or sweep out snow paths to enhance the light transmittance of the pond water.

(4) Place mousetraps and rat poison at fixed points around the overwintering ponds to prevent harm from rodents and other carnivorous natural enemies.