What feeding techniques can increase bullfrog yields?
The rearing of commercial frogs refers to the process of raising metamorphosed juvenile frogs into commercial frogs. It is the last stage of the entire bullfrog farming process and the most critical production procedure determining success or failure. At present, commercial frog farming can be divided into two methods: intensive farming and extensive farming. Extensive farming means enclosing a relatively broad area with escape-prevention facilities, in which juvenile bullfrogs are placed in this natural environment to feed on natural prey and grow naturally until they reach commercial size, when they are caught and sold; intensive farming, by contrast, requires digging smaller artificial ponds and using artificial feeding for high-density, fully artificial culture. This farming method achieves high yields and survival rates and is currently the more commonly adopted method, and it is described in detail below.
I. Construction of the rearing site
1. Frog-rearing ponds: For commercial frog rearing ponds, earthen ponds are generally dug; to save farmland and costs, they can be made by slightly renovating and modifying pond embankments, lotus ponds and small water-collection pools. The site should be chosen in flat terrain with abundant water, with an area of 100 sq m to 300 sq m, a pond depth of 0.8 m to 1 m, capable of storing 30 cm to 40 cm of water. The earthen pond must be enclosed with netting all around to prevent frogs from escaping; for high-yield intensive farming, special cement ponds can also be built, with an area of 15 sq m to 30 sq m. The pond depth is 1 m, and the water storage depends on the size of the frogs. It is made of poured concrete, with the pond bottom and walls smoothed with cement. The slope of the pond bottom should be relatively steep to ensure that one end is deep when rearing frogs, which is the main habitat of the frogs, while the other end is shallower and often exposes the pond bottom, making it convenient for frogs to come here to feed and rest; the pond bottom should also slope toward the drainage outlet to ensure the pond water can be drained dry. To prevent frogs from escaping, the top of the pond walls all around should be poured or built with an inward 10 cm lip. Cement ponds give high yields. At present, in China each sq m can produce 15 kg of frogs, making them suitable for intensive high-yield frog farming.
2. The micro-environment of the frog-rearing pond: To ensure that bullfrogs can grow and develop well, a good ecological environment should be created for them. Some aquatic plants such as lotus, arrowhead and sweet flag can be planted in the frog pond, which is suitable for bullfrogs to inhabit; on the land and slopes in the frog pond, flowers, grass and shrubs should be planted to facilitate bullfrogs resting here and to attract insects as frog feed; to prevent the impact of high summer temperatures on bullfrogs, a half-pond shade shed should be built on the south bank of the frog pond in spring, and some climbing plants such as pumpkin, loofah and grape should be planted to climb onto the shade shed, allowing bullfrogs to come here to rest during the hot season. Through such arrangements, the ecological environment of the entire frog-rearing pond becomes more suitable for the life and growth of bullfrogs.
3. Cleaning and disinfection of the frog-rearing pond: Newly built cement ponds should be filled with water and soaked for 15 days before use to remove alkalinity; when juvenile frogs are to be stocked, the old water should be drained and replaced with new water before stocking. For earthen ponds, if newly dug, they should also be filled with water and soaked for 5 to 7 days before use to remove excess heavy metal salts. Before stocking, cement ponds should also be disinfected by brushing the pond bottom and walls with bleaching powder at a concentration of 1 mg per liter or quicklime solution at a concentration of 20 mg per liter; earthen ponds should be disinfected by dissolving 90 g to 110 g of quicklime per sq m or 7.5 g to 15 g of bleaching powder in water and splashing it over the pond.
II. Stocking of juvenile frogs, feed and rearing management
The stocking density of juvenile frogs should be determined by multiple factors such as frog size, feed conditions and the level of rearing management. Earthen ponds generally stock newly metamorphosed juvenile frogs (4 g to 5 g): 100 to 120 per sq m; cement ponds can increase the stocking density by 1 to 2 times.
1. Artificial feed for frogs: In high-density intensive farming, natural prey alone can no longer meet the needs, so artificial feed must be provided. The artificial feeds currently used in frog farming mainly include insects attracted by light; live feeds such as artificially cultured earthworms and fly maggots; and artificially produced compound pellet feed. Artificially compounded pellet feed can be formulated into different specifications of particle size according to the different developmental stages and sizes of frogs. The feed conversion ratio and cost are relatively low, and in addition, some drugs can be appropriately added during formulation, which can also play a role in preventing and treating diseases. Experiments show that as long as starting from newly metamorphosed juvenile frogs, live feeds such as earthworms and small fish and shrimp are used together with static feeds such as pellet feed, so that the static feed is activated by the live feed, juvenile frogs can eat static feed, with very good results, which solves the key problem for intensive bullfrog farming.
Under artificial rearing conditions, the food intake of bullfrogs varies with temperature, frog size and feed type, and the feeding amount is roughly controlled at between 5% and 15% of the total body weight of the frogs.
2. Rearing management: Under artificial intensive farming conditions, bullfrogs eat a large amount and produce a lot of feces, which easily pollutes and deteriorates water quality, thereby causing disease. This phenomenon is more prominent when rearing in cement ponds. Therefore, cement ponds should be scrubbed frequently, the pond water should be replaced regularly, and from mid-April to mid-to-late October, disinfection should be carried out every 15 days with quicklime at a concentration of 20 mg per liter or bleaching powder at a concentration of 1 mg per liter. When the water temperature rises above 32°C, bullfrogs show reduced appetite, and if it continues to rise to 35°C, death may occur. At this time, in addition to shading with climbing plants, new water at a lower temperature from an external river should be added when necessary, and all measures should be taken to keep the water temperature in the pond below 32°C, ensuring the normal life and growth of the frogs.
Because of the high density of frogs, after a period of rearing, juvenile frogs will show differences in individual size due to uneven feeding and differences in physical strength among individuals. Bullfrogs have the bad habit of eating smaller ones, so they should be promptly divided into separate ponds according to size to increase the survival rate of the frogs. When the size reaches 25 g to 50 g, adjust to 60 to 80 per sq m; when the size reaches 100 g, adjust to 30 to 40 per sq m; when the size reaches 150 g, adjust to 20 to 30 per sq m.
Bullfrogs are good at climbing and jumping, so escape-prevention facilities should be checked frequently, and any damaged parts should be repaired promptly. Watch frequently for enemies such as snakes and rats, and once found, kill them promptly to ensure the safe growth of the frogs.