Key Points on Breeding and Hatching Techniques for Southern Farming of the Chinese Brown Frog

Breeding and hatching technology is one of the key techniques for southern farming of the Chinese brown frog. Generally in early March, before the water temperature rises to 10°C, preparations for breeding must be made: disinfect the constructed spawning pond trenches and hatching ponds (the original hibernation ponds, spawning ponds, hatching ponds, and rearing ponds can be used), and fill them with clean water, adjusting the water temperature by regulating the water level and light. Once everything is ready, the Chinese brown frog breeding frogs can be placed into the spawning and hatching ponds.

Getting the Chinese brown frog to spawn and hatch tadpoles is relatively easy, but without good farming techniques, it is difficult to achieve the ideal result of both the spawning rate and hatching rate exceeding 90%. Therefore, the issue of breeding and hatching technology must never be neglected.

1. Breeding Techniques

(1) Disinfection and pairing: After moving the Chinese brown frogs out of the overwintering pond, first give them a medicinal bath in a potassium permanganate solution at a concentration of 5×10-6 for 5 minutes, then move them into the spawning pond. The stocking density of breeding frogs in the spawning pond is generally about 30 pairs/sq m, the water level is maintained at 10-15 cm, and the water temperature at 10-15°C. After the Chinese brown frogs pair up in amplexus, if the weather suddenly turns cold, spawning will be delayed, and the Chinese brown frogs that have already paired may hibernate again together. Also, because this is southern farming, and in order to strive for a high maturity rate of marketable frogs within the same year, the earlier the spawning the better. Therefore, it is best to spawn inside plastic greenhouses.

(2) Spawning: When introducing breeding frogs in spring, under normal conditions, the breeding frogs will pair in amplexus and spawn within 3-5 days after entering the spawning pond. When the temperature is relatively high, they often all finish spawning within 1-16 hours after the breeding frogs enter the spawning pond. Therefore, when introducing breeding frogs in spring, one must always be ready to place the breeding frogs into the spawning pond, so as not to miss the spawning opportunity, which would cause premature spawning or difficult spawning in the Chinese brown frog.

After the Chinese brown frog is moved south, due to insufficient overwintering depth, relatively large temperature changes in spring, or human disturbance, difficult spawning often occurs. That is, the female frog can normally release eggs, and the female and male frogs can normally pair in amplexus, but the female frog cannot lay the eggs due to endocrine disorder, and most will die as a result. At present, there is no good remedy.

(3) Post-spawning dormancy: Under normal conditions, the Chinese brown frog mostly spawns in the early morning. The newly laid egg mass is about the size of a chicken egg; at this time, do not rush to scoop it out. Before the egg mass has absorbed water and expanded, scooping it out too early will affect fertilization and hatching. However, the breeding frogs can be scooped out after spawning, separated by sex, and placed in a post-spawning dormancy site with a good ecological environment, protected from light, moist, and with hiding places. Otherwise, because of the high temperatures in the south, the frog's dormancy period will be short or it may not even become dormant, resulting in an excessively high mortality rate. At this time, dead frogs should be promptly removed, the rearing site should be disinfected, and sufficient bait should be supplied.

(4) Ratio of female to male breeding frogs: According to natural conditions and usual farming practices, the pairing ratio of female to male frogs is 1:1, and it is required to add 10% more males. Based on many years of Chinese brown frog spawning experiments, Fengkang Company has demonstrated that the ratio of female to male frogs can be 70:30. Because spring temperatures in the south are relatively warm, after the female frog's eggs mature, stimulated by the croaking of the paired male frogs around it, it can spawn alone even without pairing in amplexus. At this time, as long as the sperm released by the male frog is normal and healthy, within the 10 hours of sperm survival, the eggs laid by the unpaired female frog can combine with the sperm in the water, completing external fertilization and proceeding to hatching. Because one female frog can lay 1,300-2,300 eggs, while one male frog releases millions to tens of millions of sperm, far more than the number of eggs, and moreover the paired breeding frogs in the spawning pond cannot all spawn at the same time, since there is always a sequence, the number of female frogs in the spawning pond can be increased to ensure there are sufficient eggs to combine with sperm, producing as many fertilized eggs as possible.

The conditions for the success of this experiment are: the spawning pond is level, the water temperature is 10-18°C, and the water body is absolutely clean and not flowing. This 70:30 female-to-male ratio exactly coincides with a 70% female induction rate and 30% male rate, which helps to fully implement female induction in the future for large-scale spawning and hatching without worrying about the proportion of male frogs being too low.