Detailed Explanation of the Key Breeding Techniques for Rana chensinensis Farming

The breeding techniques for Rana chensinensis are a major part of production, and the level of breeding technique directly affects the profitability of artificially farming Rana chensinensis. The breeding techniques for enclosed-gully frog farming mainly include seed selection, egg laying, hatching and rearing.

Seed eggs and seed frogs

At present, frog farming production is mainly based on seed eggs, with seed frogs as a supplement; most are collected from the wild, either by catching (collecting) them oneself or by buying them. 1. Collection and transport of seed eggs. Collecting seed eggs in spring saves time, effort and cost, and is currently the method commonly adopted by farmers. In static water areas such as natural ponds and marshy wet meadows, use a scoop net to gather egg masses. In principle, the earlier the collection time, the better. Newly laid egg masses are small in size, highly elastic, not easy to break apart, and convenient to transport, because the peak egg-laying period of Rana chensinensis is from 5—8 a.m., so the best time to scoop frog eggs is from 6—11 a.m. Buckets can be used as transport tools for seed eggs. For long-distance transport or for frog eggs that were laid a relatively long time ago, a small amount of water should be sprinkled into the bucket to prevent the egg masses from sticking to one another.

2. Collection, transport and selection of seed frogs. 1. Spring collection. Rana chensinensis generally emerges from the river from early April to mid-April each year, and from mid-April to the end of April, when the water temperature is 10—11°C, it begins to lay eggs. Therefore, spring collection of seed frogs should be done promptly, catching them in rivers, marshes or natural ponds in the field.

2. Autumn collection. From mid-September to mid-October each year is the time when Rana chensinensis comes down the mountain and enters the river; during this period, large numbers of seed frogs can be caught. Seed frogs should be caught by netting, hand-catching and trap-pot catching; it is strictly forbidden to catch them by methods such as chemical agents or electric shock.

3. Buying. At present, many frog farming households adopt the method of buying seed eggs and seed frogs. This is an important way to solve the problem of seed sources and can supplement the insufficiency of self-caught amounts, but attention should be paid to timing when buying seed frogs in spring. Female frogs after ovulation prepare to lay eggs the following year; because the recapture rate is low, the results are not great.

4. Transport of seed frogs. No matter what method is used to obtain seed frogs, injury must be avoided. Seed frogs must be packed in gunny sacks or baskets, and must never have thread, wire, etc. passed through the eyes, nostrils or upper and lower jaws. For long-distance transport, they should be held in cages or baskets, with coverings such as rice straw added inside the cage, and water sprinkled frequently to maintain humidity; midway, they must be rinsed with clean river water to avoid death caused by drying of the frog bodies. When transporting seed frogs, it is not necessary to transport them with water. In spring transport, timing must be well controlled and long-distance transport should not be undertaken; if it exceeds 5—6 days, the seed frogs will discharge unfertilized eggs without “amplexus”.

5. Selection of seed frogs. At present, there are still no selection standards for seed frogs. Based on the growth cycle of Rana chensinensis and practical experience in recent years, seed frogs should be selected at 3—4 years of age, robust in constitution, weighing about 50 grams, and with a standard body color, that is, dark brown is better.

Egg-laying methods

Artificially constructed egg-laying sites differ greatly from natural egg-laying sites, and the density of artificially bred seed frogs is high, so Rana chensinensis is unwilling to lay eggs in the egg-laying site. Therefore, under artificial control, they must be forced to lay eggs in the egg-laying site. The egg-laying methods can use the cage-type egg-laying method and the enclosure-type egg-laying method.

1. Cage-type egg-laying method. Use fine wire or branches to weave a cage, place good seed frogs into it at a male-to-female ratio of 1:1, then place the cage into the egg-laying pond, and properly adjust the water depth so that the water depth in the cage remains at about 15 cm. The egg-laying cage should be placed in a static water area, far from the outlet and inlet. After the seed frogs pair up, when the water temperature is about 10°C, they can lay eggs in 7—8 hours. Attention should be paid to accurately grasping the time, promptly moving the frog eggs to the hatching pond, and taking out the seed frogs after egg laying and sending them to the dormancy site. If the egg-laying pond, hatching pond and rearing pond are built according to unified standards, several ponds in the middle and upper reaches can be selected as egg-laying ponds.

2. Enclosure-type egg-laying method. Surround the egg-laying pond with plastic film or wire mesh. The plastic film or wire mesh is 1—1.5 m high, inclined inward at an angle of 45—60°, or folded inward at a right angle at the upper end, with the lower end compacted with soil. Place seed frogs at a male-to-female ratio of 1:1, with a density of 10—15 pairs per sq m as appropriate. In order to increase the pairing speed, about 10—20% more male frogs can be added. After egg laying, egg masses and seed frogs should also be moved promptly. If the egg-laying pond, hatching pond and rearing pond are built according to unified standards, the entire breeding site can be enclosed, which facilitates management and is extremely convenient and feasible.

III. Hatching methods

Practice has proved that using the natural hatching method is relatively good. Natural hatching means frog eggs rely on natural water temperature to hatch, basically similar to the hatching method of natural wild frogs, namely: place the eggs in the hatching area at a quantity of 15 masses per sq m and let them hatch and grow naturally. During the hatching process, several issues should be noted: First, during hatching, place the egg masses in shallow water, and after the egg masses expand, move them to deep water. If they are placed directly in deep water, because the egg masses have not expanded, their buoyancy is small and they easily sink to the bottom and become polluted; in addition, the water temperature in deep water is low, hatching speed is slow, and frog eggs are easily damaged and wasted. Second, in the early stage of hatching, adopt same-side water intake, outlet and closed (semi-closed) irrigation methods to maintain stable water surface and water temperature. The water depth in the pond should be about 20 cm—30 cm, and at night, because the air temperature is lower, covering is required. Third, attention should be paid to preventing egg masses from being polluted by mud. Use wormwood stalks, branches, etc. to build small squares on the pond surface, controlling the egg masses in a certain area to avoid drifting to the pond edge and becoming polluted. Fourth, attention should be paid to preventing harm from natural enemies, and domestic poultry should be driven away promptly, especially natural enemies such as domestic ducks and frogs. Fifth, during the hatching period, attention should be paid to maintaining a quiet environment, avoiding vibration of the pond ridge, and not stirring the stored water in the hatching pond. Sixth, during the hatching period, the water temperature should be controlled at about 10—15°C. Expert experimental research results show that at this water temperature, the proportion of female frogs can be increased by 20—30%.