The cage material with stocking density requires good ventilation and water permeability, and generally plastic nets or screens can be sewn. The specifications and shapes of cages should be adapted to local conditions, generally rectangular, and the volume should not exceed 10 cubic meter. After sewing the net, bamboo pieces or wooden strips can be tied into a box frame, and the net can be fixed or completely opened. When installing a cage in a pond, you can tie a foam board or floating objects at the place where the cage enters the water 30 cm to ensure the stability of the water level in the cage, and pull it along the coast with ropes to prevent strong winds from blowing. The cage culture of bullfrog should make full use of the water in the cage for high-density culture, and the size of the cage where bullfrog hatches is 120? 80? 40 cm, 40 mesh nylon net, fixed with wooden frame, about 6000 fertilized eggs per square meter (about a nest). Generally, the density of tadpoles is 300-500/m2, young frogs are 50-200/m2, and adult frogs are 80-0/00/m2. Because bullfrogs are kept in cages with high stocking density and concentrated frogs, preventive disinfection should be done in advance. Generally, every 10 day, spray box with L international unit bleaching powder solution for disinfection. After the bullfrog is put into the cage, it should be divided into boxes and graded according to the growth rate to avoid unnecessary losses caused by cannibalism of the same kind.
In estrus management, bullfrogs are hermaphroditic. When breeding, mature individuals dives into the water to get a suitable pair. The female ovulates and the male ejaculates in the water for in vitro fertilization, which is a typical representative of frog breeding. The gonad development of bullfrog usually takes about 8 ~ 9 months from tadpole hatching to sexual maturity. The sexual maturity of bullfrog varies greatly with temperature, food and feeding methods, and it can be fed in pairs at the ratio of 2: 3 per 10 square meter or 1: 1. The female frog weighs about 350 grams, and the male frog weighs more than 300 grams. Sexually mature male and female bullfrogs have obvious estrus behavior under the influence of external environmental factors such as temperature and light. In the early estrus, the behavior of the male frog is to constantly call the female frog, with an average of more than 100 times per hour, and there is chasing behavior. The male frog grabs the female frog and touches her submandibular chest with his fingers, and the left and right forelimbs will quickly close and hug together. It can be seen that the medial marriage tumor at the base of the first limb of the forelimb is particularly obvious and is flesh red. The female frog in estrus does not eat food, but jumps into the male frog's song, and sometimes clicks in response, indicating that the female frog has a courtship request. At this time, the female frog let the male frog jump on its back and hug it. When estrus reaches its climax, men and women embrace each other, usually in the middle of the night, and the hug time is usually as long as 1 ~ 2 days. The breeding season of bullfrog is from April to September, which varies from early to late in different regions. The external conditions for spawning are not high, and the key is temperature. As long as the water temperature reaches 20℃ ~ 30℃, both ponds and rivers can give birth smoothly. The ideal environment requires quiet, leeward, few pedestrians and aquatic plants on the shore. At the end of the hug, the female frog is stimulated by a foreign body, which is transmitted to the central nervous system through the sensory organs and then reaches the pituitary gland, prompting the pituitary gland to secrete hormones. Under the action of sex hormones, the female frog pushes back hard, the abdomen contracts with the help of the male frog's breathing and cuddling, and the eggs are excreted. At the same time, the male frog excretes semen for in vitro fertilization.
The fecundity of bullfrog managed in egg period is the strongest among frogs. The absolute number of pregnant eggs of one-year-old bullfrog is about 6.5438+0.5 million, which increases with the increase of age, body length and weight. Except for age and weight, there are great individual differences in the absolute number of pregnant eggs, and females with good nutrition and normal development are relatively better. Therefore, in order to obtain greater fecundity, we must pay attention to the purification and cultivation of farmed frogs. Bullfrogs lay eggs many times a year, and naturally lay eggs 3 ~ 5 times a year. Under the condition of artificial feeding, if the temperature can be controlled at 25℃ ~ 30℃, eggs can be laid all year round. Ovulation time every time 10 ~ 20 minutes, the average individual ovulates 20 ~ 30 thousand, up to 50 thousand. Bullfrog eggs are round and divided into two poles. Animals are extremely black and plants are extremely gray. Some newly laid animals and some newly laid plants are at the top of the world, so the newly laid eggs are black and white and numb. About 30 ~ 60 minutes after laying eggs, all animals face up, which is called automatic transposition of eggs. If there are white plants on the egg after 2 hours, it is an unfertilized egg. According to this, the fertilization rate of bullfrog after spawning can be calculated, and the general fertilization rate is above 90%.
There are many reasons why bullfrogs are not fertilized when laying eggs, mainly because the water temperature is too low and the water quality is not clean; The male frog is too old, too weak, too old. Generally, the second-year-old frog has the highest fertilization rate, while the third to fourth-year-old frog has a lower fertilization rate. The imbalance between men and women, too many or too few men, all have an impact. The normal sex ratio is 1∶ 1, and the fertilization rate is over 90%. The fertilization rate of 2∶ 1 is 75% ~ 80%, and that of 3∶ 1 is only 40% ~ 50%. The water surface is too wide for spawning. There are many ways to improve the fertilization rate, and artificial fertilization is an effective shortcut, and the fertilization rate can reach 90% ~ 95%. Fish out the egg pieces in time, usually 30 minutes after spawning, to avoid the egg pieces softening for too long and sinking into the bottom of the pool to reduce the hatching rate, or animals such as frogs and fish disperse the egg pieces or swallow the frog eggs. Appropriate environmental conditions can improve the hatching rate of tadpoles, otherwise it will reduce the hatching rate. The suitable water temperature for incubation is 25℃ ~ 30℃, and should not be lower than 16℃ or higher than 34℃. Tadpoles can hatch at 19℃ ~ 27℃ for 3 ~ 4 days. Tadpoles can hatch for two and a half days at 25℃ ~ 30℃.
Disease control aquatic insects larvae and adults are the main natural enemies of bullfrog eggs and tadpoles in the early stage; Young frogs and birds are the main enemies of tadpoles in the later period; Animals and reptiles are the main enemies of adult frogs. As long as you pay attention to food hygiene and water quality hygiene, you are generally not easy to get sick. Common diseases are as follows:
Wheel disease. The disease is caused by rotifer, a protozoan, and often occurs in ponds with high density and slow development of tadpoles. The sick tadpole is covered with rotifers. With naked eyes, tadpoles' tails are white and often float on the water. In order to reduce the stocking density and expand the water body where tadpoles move, the whole pond should be covered with a mixture of copper sulfate and ferrous sulfate of 5: 2, so that the concentration of pond water can reach 1.4 international units.
Foam disease. The diseased tadpole swelled, lost its balance and swam back to the surface. Anatomy shows that the intestine is full of gas. During the high temperature period, fresh water should be replenished every 2 ~ 3 days, and a shed can be set up to shade and cool down; Take out the sick tadpoles and put them into cooler water, sprinkle with 20% magnesium sulfate solution, and put them into the tadpole pool after 1 ~ 2 days.
Gastroenteritis. The disease is rapid and harmful, which is caused by bacteria or indigestion. The sick tadpole has gastrointestinal inflammation and congestion, and the anus is red and swollen; Young or adult frogs are weak and can lead to death. Can be soaked in 0.05% ~ 0.0 1% salt solution. Before stocking, the tadpole pond should be cleaned and disinfected, with 75 kilograms of quicklime per mu, and moldy and deteriorated feed should not be fed. The residual bait on the bait table is cleaned up and the bait table is scrubbed every day. In addition to keeping the water fresh, the whole pond is sprinkled with bleaching powder once a week, so that the bleaching powder content in the pond water is 1 ~ 2 international units.
Red leg disease. The disease mostly occurs in ponds with high density and poor water quality. The skin between the thigh and abdomen of the sick bullfrog is red, the hind limbs are weak, and the head is prone on the ground, so it can't eat. Death after 3 ~ 4 months is the most common and dangerous disease in bullfrog breeding. Frog ponds should be disinfected regularly with quicklime or bleaching powder to keep the water clean, so as to improve the water quality, appropriately reduce the breeding density and isolate sick frogs in time. The diseased frog can be cured by soaking in 20% sulfanilamide solution for 24 hours, or soaking in 2% ~ 5% salt solution 15 minutes, once a day 1 time for 3 days.