The breeding of A. tilapia requires no artificial aphrodisiac spawning and water stimulation. As long as the water temperature is stable above 18°C, the mature female and male broodstock are placed in the same breeding pond until the water temperature rises to 22°C. Can naturally breed fry. In the case of a water temperature of 25-30°C, hybridization can be performed once every 30-50 days.
(I) Preparation of broodstock breeding pond
1, the choice of breeding pond
The quality of broodstock breeding pools directly affects the broodstock spawning, hatching, and fry survival rates. When choosing a broodstock breeding pond, consider the following aspects:
(1) Location: The breeding pond should be selected where the water quality is good, the water source is sufficient, the water injection and drainage are convenient, and the environment is quiet. Do not have tall trees and houses around the pool.
(2) Area and water depth: The breeding pond area is generally 0.5-2 mu. When a broodstock first enters a breeding pond, the water depth is 1-1.5 meters. When the broodstock is crossbreed, the water depth is 0.8-1 meters.
(3) Shape and soil quality: The shape of the breeding pond is preferably rectangular in the east-west direction. There must be shallow-water beaches along the pool to facilitate digging nests for spawning. Loamy soil or sandy loam soil is better, the bottom should be flat, can not grow aquatic plants.
2, the breeding pond
Before the broodstock is stocked, the breeding pond must be cleaned and disinfected to create excellent living environment conditions for the broodstock, which is conducive to the breeding of broodstock.
The pool water is generally drained in the winter or early spring. Excessive silt is removed, the bottom of the pool is leveled, pool drains and leaks are repaired, and weeds are removed. Then clear the pond again 10-15 days before the broodstock is stocked. The commonly used clear pond medicines include quicklime, bleaching powder, etc., of which the quicklime is best, which can not only kill the wild fish in the pond, but also kill the living organisms and pathogens, and can also play the role of fertilizer and water. Clear ponds should be carried out at noon on sunny days to improve efficacy.
The clear pond method is to discharge the pool water, leaving 5-10 centimeters of water left at the bottom of the pond, and use 60-75 kilograms of lime per acre. The lime is first added into the slurry and then the whole pond is splashed or bleached to clear the pond. In kilograms, the whole pool is splashed immediately after the bleaching powder is dissolved in water. The effect is the same as raw lime.
3, base fertilizer
After clear ponds, 5 to 7 days before the broodstock is stocked, fill the pool with 1-1.5 meters of fresh water. When using water, use a dense mesh filter to prevent wild fish and other harmful organisms from entering the pond. And apply basal fertilizer to cultivate abundant natural food for broodstock feeding. Base manure has manure (pig manure, cow dung, human waste, etc.) and green manure. Generally, 500-600 kg of manure is applied per mu or 400-500 kg of green manure. Manure should be diluted with water after fermentation. Quanchiposa; Green manure piled up in shallow water near the pool, making it rot decomposition.
(B) broodstock rearing
1, broodstock selection
The broodstock used for cross breeding must be carefully selected to ensure good heterosis. The broodstock is generally selected twice a year, and the broodstock is selected once into the overwintering pool. After winter, it is selected once when it is moved into the breeding pond. When choosing broodstock:
The first thing to pay attention to is choosing purebred broodstock. Generally, they can be selected based on their characteristics, body color, and the like. The main characteristics of Nile tilapia and Oriya tilapia are:
Nile tilapia - yellow-brown body color, with nine vertical black stripes on the side of the body, black edges of dorsal fins and caudal fins, 9-10 dark vertical stripes on the tail fins, and gray pelvic and anal fins.
Oreochromis auratus - body color is blue-violet gray, with 9-10 vertical black stripes on the side of the body, the dorsal and caudal fins are red at the end, there are many yellowish squatting spots on the caudal fin, but do not form vertical stripes, pelvic fins Anal fins are dark blue;
The second should pay attention to individuals with good body shape, high back body thickness, normal color, clear markings, and good development.
The third is to choose individuals who grow fast, have large individuals, have strong physique, and have no injury or disease. Generally, the females of Nile tilapia have a body weight of 150 g or more, 250-500 g is better, and Oriya tilapia Male individuals are slightly more important than Nile tilapia females.
Finally, we must also pay attention to the feeding conditions of the broodstock, and use it at low temperatures for winter and culture at room temperature. Breeding at high temperature and constant temperature often leads to degradation of broodstock, slower growth of offspring, and smaller sexual maturity.
2. Difference between male and female
The differences between male and female tilapia are mainly identified from their abdominal reproductive pores. Nile tilapia and Oreochromis niloticus are not easily distinguishable between young and female. After sexual maturity, their reproductive pores can be distinguished with the naked eye (see figure).
Female abdomen has three openings, namely the anus, gonopore and urinary holes. The urinary tract is at the top of the genital process, and the gonopore is between the urinary tract and the anus.
There are only two openings in the male's abdomen, namely the anus and urogenital holes. Its urinary tract and genital hole are combined into one opening, collectively referred to as the urogenital hole. The urogenital hole opens at the top of the reproductive process and is only a small spot, which is not easily visible to the naked eye. During the breeding season, the genital process often droops slightly, and white seminal fluid flows out of the abdomen.
3, stocking time
The broodstock restocking time varies with the climate of each place. The specific restocking time depends on the local temperature and water temperature. As long as the water temperature is stable above 18°C, the broodstock can be put into breeding ponds. The Yangtze River Valley is generally stocked at the end of April and early May, and Guangdong and Fujian are stocked about mid-to-late March, and the north is stocked about mid-May. The stocking of broodstock should be carried out in a sunny and weatherless environment, and once stocking is good, the broodstock can be spawned at a concentrated time, which is consistent with seedlings and is conducive to the cultivation of seedlings.
4, male and female matching group
When stocking broodstock, the ratio of female and male broodstock should be appropriate, generally 3:1 or 4:1; preferably, more females than males.
5, stocking density
The broodstock stocking density is calculated on the female. According to the size of the female fish, 1-2 tails can be placed per square meter. Generally, the female fish of 250-500 g/tail are reared with 600-750 tails per acre. If males and females are grouped by 3:1, 200-250 tails are used for male and female fish. Individuals of broodstock are 150-200 g/tail, and about 1,000 tails per mu can be stocked.
(three) broodstock breeding
After passing through the winter, the broodstock has a weaker constitution and poor gonadal development. It is necessary to strengthen cultivation so as to achieve early egg production and early seedling production.
After the broodstock is moved into the breeding pool, fertilize and feed regularly. Fertilization should grasp the principle of less quantity and more time, generally every 5-6 days per mu of fermented manure 100-200 kilograms or green manure 200-300 kilograms. The weather is clear, the water is lean and the fish activity is normal. Fertilizer can be given as much as possible. Otherwise, it will be less or not applied to control the water quality. If the water quality is too fat, fertilization should be stopped, and new water or oxygen should be added immediately to prevent spawning and spitling caused by broodstock floating heads.
In order to promote the development of gonad gonads, artificial diets should be fed once or twice a day. Commonly used feeds include bean cakes, vegetable cakes, peanut cakes, rice bran, bran, and corn flour. Olivia tilapia is omnivorous. Do not feed a single feed for a long period of time. It is best to mix several types of feed. Feeding amount is generally 3-5% of the total weight of the fish. After the fish is fed, the fish is eaten quickly, and the feed amount can be increased appropriately. Otherwise, feed or feed is stopped.
(four) to grasp the broodstock spawning date
After the broodstock is stocked, when the water temperature rises above 22°C, it begins to lay eggs and emerge. At this time, you should often visit the pond to observe the activities of the broodstock and to know the date of spawning and the emergence of the broodstock.
When the water temperature is around 20°C, the broodstock begins to estrus. It is common for male fish to dig their nests with mud in the shallow water near the pool. When digging a nest, the males pose vertically and open their mouths to bite the mud from the bottom of the pool and land on the sides of the nest. Repeat this several times to dig into a spade-shaped spawning nest. At this time, males often induct sexually mature females into nests. Soon after the females lay their eggs, the males immediately ejaculate. After the eggs are fertilized, the females hatch the eggs immediately. At a water temperature of 25°C, a small flock of small groups of swimming fish can be seen on the poolside about 15 days later.
(five) fishing seedlings
Seedlings are usually taken in the morning or in the evening to see more time.
At present, the better fishing method is to use a net or a small trawl, fishing around the pond. It operates lightly and does not require watering. It can be harvested many times, and has high seedling yield. The fry is not easy to be injured, and it will not affect the broodstock cross breeding due to the water. Remove the fish fry first held in a cage, until a certain amount of fish, you can put a few into the breeding pond for seedling cultivation. The number of fry is generally taken by sampling counting method, that is to choose a representative cup count, and then calculate. The total mantissa = cup number per cup mantissa.
O. tilapia has the habit of large fry to eat small fry, 2-3 cm juveniles can catch fry just out of broodstock, so need to use net to catch fish seedlings in ponds every 10-15 days. .