The species of the order Milkweed (Oceanoptera), Blindidae, Milkfish, Milkfish. In Taiwan, it is known as Milkfish, Scaly larvae, Anping fish, National holy fish, Harbour fish, and Mackerel. This genus is only one species in our country. Milkfish is a broad-salt fish with fast growth, large individuals, and a wide range of food habits. It is one of the fish cultured in Hong Kong and it is the main breeding target in the coastal areas of Southeast Asia. As early as the 17th century, Taiwan began to breed in China, and the scale of development was relatively large. Milkfish breeding conditions are simple, but there are insufficient sources of nursery. One of the keys to the breeding of milkfish is how to solve the supply of seed. Natural fishing is mostly in the spring and autumn. Hong Kong fish rearing will be seeded in spring and caught in late autumn. Two ways to obtain mature broodstock are to capture sexually mature broodstock directly from the sea or hormone-induced induction of immature fish. First, the time and method of catching broodstock fish caught in non-breeding season can be used as a back-breeding broodstock, when harvesting more than 3 kg in weight is better. In the breeding season, broodstock with better sex gland maturity can be harvested. Milkfish of the milkfish have a monthly cycle, for example, more mature wild broodstock can be caught one week before the full moon, while in the Philippines, broodstock have the largest number of eggs laid around the moon. Fishing broodstock can use gill nets, fences and custom nets. Gillnets can be applied to any water area; seine nets are suitable for shallow water bodies and partially or fully enclosed water bodies; various custom nets can be used for deeper open waters. Second, the transport and handling of broodstock Short-distance transportation of milkfish can be carried out by hand-cutting nets or plastic bags filled with water. Long-distance transport uses transport barrels that can be manually controlled. 177 6- to 8-year-old broodstock are transported in a 52-meter-wide water tank with a depth of 0.6 meters, with an average weight of 2.16 kg, 20 barrels per barrel, and a salinity of 7 to 10, cooled by ice packs, filled with oxygen and transported for 18 to 28 hours. The survival rate after transportation was 85%. The fat eyelids of milkfish are often injured and turbid during transportation. They often recover from symptoms when they are light, and they can lose sight and die when symptoms are heavy. Can be treated with antibiotics such as nitrofurazone. The use of anesthetic agents or HCG administered to fish at a dose of 555 IU/kg body weight after transportation can effectively prevent degeneration of the gonads due to broodstock stress. Before oxytocin, the female broodstock should be gradually overgrown with a salinity gradient of 1 to 4 to a salinity of 35. Third, the broodstock to cultivate gonads mature and spawning conditions bait must contain 32% to 40% of the protein can promote gonad maturation. The feed can be gluten, wheat flour, soy flour, squid compound feed, squid feed, squid feed, shrimp granule feed, and mixed fish, crustaceans and the like. In high-salinity ponds, Artemia is an essential feed for sexual maturity of milkfish. The amount of food fed is 2% to 5% of the fish's body weight. 1. The minimum water temperature for sexually mature fish is 20 °C, and the minimum temperature for spawning is 24 °C. Mature broodstock can be obtained at 25-31, 21.4- 30.7, and 24-26. With the method of implanting LHRH-A particles, broodstock can mature at 20°C to 22°C. 2. Salinity Milkfish can mature within a wide range of salinity, with a minimum salinity of 8 and natural maturation at salinity of 39. Vesselfish spawning can only be at or above standard seawater salinity. And may be inhibited by drastic changes in salinity. Milkfish can be laid in inland salt lakes with a salinity of up to 13. 3. Illumination intensity of light stimulates the maturation of the gonads of the milkfish, but it is not a determinant factor for maturity and oviposition. Fourth, the broodstock feeding facilities broodstock can be matured in the earthen pond, and can be combined with hormones and photoperiod treatment. The broodstock ripening facilities also include outdoor and indoor round and square earthen ponds, concrete pools, fiberglass weeds and canvas pools, with water change and air supply systems. 1. Density and sex ratio The broodstock stocking density is 20 cubic meters/tail to 40 cubic meters/tail and 2.3 cubic meters/tail to 5.7 cubic meters/tail. The ratio of female to male is generally 1:1 to 1:2. 2. Induction of mature milkfish. The time required for the fish to reach sexual maturity under stocking conditions is long and it is difficult to achieve natural maturity. Artificial induction of maturation is required. Induction usually takes place two months before the start of the breeding season. More effective induction methods include hormone treatment, control of photoperiod, hormone treatment and control of photoperiod combined with three methods. The hormone treatment method was to implant 200 μg LHRH-A pellets once a month and one 250 μg 17-methyl testosterone capsule once every 3 months. 3. The photoperiod rule is that light is applied every 6 months for 6 hours per day, 18 hours dark to 12 hours light, 12 hours dark to 18 hours light, and 6 hours dark. With the above methods, both male and female broodstocks can be matured and spawning can be induced. V. Spawning 1. Induced spawning Under artificial breeding conditions, female fish rarely reach natural spawning. Therefore, hormone injection is required to induce spawning. The broodstock is also induced by hormones and can also spawn naturally, but this opportunity is also very rare, and it is often unsufficient or the fertility rate is low. In most cases artificial egg fertilization is used. Before inducing spawning, the oocyte diameter must be above 660 microns. A single injection of 10,000 international units of HCG/kg of body weight or a single injection of 250 micrograms of LHRH-A/kg of body weight 1 to 5 times. The ovulation tube was used to check the development of the egg and the male abdomen was gently pressed by hand to observe the sperm maturation. If the female gonad reaches the final maturity, the sperm and egg can be extruded to perform artificial insemination. 2. Spermatozoa Preservation of milkfish serum is the best preservation solution for cryopreservation of milkfish, while dimethyl sulfoxide is a better antifreeze than glycerol. The milkfish stock preserved in liquid nitrogen has a higher fertilization rate and hatchability and a higher survival rate of larvae than fresh semen and semen kept at near zero degrees. 3. Egg characteristics, egg formation and embryo development Eggs are transparent round, no oil globules, egg diameter 1.2 mm, yellow. Fertilized eggs sink to the bottom of the sea in salinity of 30. When the salinity is higher than 34, fertilized eggs float on the surface of the water. The fertilized eggs were inflated in seawater with a salinity of 30 to 34 and a water temperature of 26.4 to 29.9°C. After hatching from 25 to 28.5 hours, the hatching rate could reach more than 80%. After hatching, the eggs were transferred to seedlings for cultivation. When the salinity is less than 5, the eggs are not refined. When the salinity is less than 16, it can be fertilized but cannot hatch. Therefore, when the salinity is less than 16, the milkfish cannot breed.
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