Milkfish (Chan0s chan0s), also known as milkfish, common name is fish, sea fish and so on. It is classified in the order of Oystercatcher, Blindfish suborder, Milkfish, Milkfish. Because milkfish has wide salinity, low oxygen tolerance, strong disease resistance, wide feeding and fast growth, it is suitable for artificial breeding. It is the most successful type of pond culture in marine fishes, and it is well known in brackish water culture.
I. Biology of Milkfish (1) Morphology and Distribution Care of the fish body is prolonged and slightly flat, slightly spindle-shaped. Sideline is complete. The head is medium and large, blunt. The mouth is small, the kiss is not prominent, the end position. Eyes are large, fat eyes are thick and well developed, completely covered by the eyes, hence the name. The upper and lower jaws had no teeth, and the maxillary median had 1 depression. The lower sutured site had 1 protrusion and the upper and lower concave and convex were embedded. The body is finely rounded, with no scales on the top of the head, and there is a scale at the base of the dorsal fin and anal fins. The base of the pectoral and pelvic fins has a scale. The base of the caudal fin has two large scales. The pelvic fins are located below the dorsal fins and the caudal fins are deep forked The upper part of the dorsal and lateral side of the body is shiny blue-green, and the lower side of the body to the entire abdomen is shiny silver-white. Each fin is slightly black. Milkfish inhabits tropical and subtropical waters and is widely distributed in the Pacific Ocean, Indian Ocean, Red Sea, and East African coast. Our country is found in the South China Sea and the South China Sea, occasionally seen in the Yellow Sea.
(b) Adaptation to the environment The fish is a warm-water fish, and its optimum temperature range is 15-40°C. The optimum temperature is 28-35C and less than 10°C. Milkfish is widely salty and can live in seawater, semi-water and fresh water.
(3) The dietary milkfish is mainly eaten by plants, mainly feeding at the end of diatoms and organic detritus. Small crustaceans, rotifers. Mollusks, etc. can also be ingested. Under artificial breeding conditions, the milkfish of the milkfish mainly ingested diatoms, cyanobacteria, and green algae. Protozoa and copepods. Small crustaceans such as Ostracoda also feed on some organic debris. The 50-100mm body length of fish species is blue-green algae, protozoa, copepods, small crustaceans and organic detritus. When food is lacking, some filamentous algae are also ingested. Rice bran, bean cakes, peanut cakes and artificial diets can all be used as feed for the growing season.
(d) The growth of milkfish grows quickly and the fry is kept for 1 month, and the body length is 5-7 cm. After 2 months, body length can reach 12-15cm. 8-10 months up to 35-40cm, weight 250-500g, that is up to market specifications. If you keep 5-6 years in a pond, your weight can reach 4kg. The largest individual body of adult fish is up to 150cm in length and 15kg in weight.
(e) Breeding of milkfish has a marked migration habit of landing in the sea. Spawning grounds are usually about 5-15 nil of sandy or coral bottom offshore. Clear waters, water depth 20-30m, salinity 28-34.5 ‰. The milkfish male body is 94cm in length and females begin sexual maturity around 100cm. Sexual maturation age is 6-9 years old, mostly 8-9 mature. The females with about 100cm body length have 3-10 million eggs, and the large individuals can reach 10 million eggs. There are two breeding seasons for milkfish in a year, namely April-June and August-September. During the reproductive season, spawning takes place at the height of the full moon and new moon. Spawning takes place in the middle of the night. Fertilized ovoid, transparent, slightly yellow, with detailed cracking stripes. Egg diameter 1.12 to 1.23mm, no oil balls. It is semi-suspension in seawater with a salinity of 30 , or more and is evenly distributed in surface water. Fertilized eggs can hatch for about 20-30 hours.
In the natural sea area, approximately two and a half days after hatching, the larvae with yolk sac begin to migrate to the coast and arrive at the coast between 10 and 15 days of age. In the shallow marine waters with rich accumulation of bottom layer organic matter and bait organisms (blue-green algae and diatoms), they have developed into juveniles for a period of approximately 4 weeks. Juveniles live in the above-mentioned waters and grow to 1 year of age. When they weigh more than 250g, they swim to the deep sea until they are sexually mature. They then swim to lay eggs in the shallow sea near the shore to breed. Milkfish can grow up to several kilograms in brackish water or even pure fresh water, but the general glands cannot mature and must migrate to higher salinity waters to reach sexual maturity. In the rearing condition, the gonads of the milkfish are not developed. The main reason is that the breeding pond feeds more food containing animal protein, resulting in a higher fish body fat, inhibiting the development of gonads. After switching to bait containing more plant protein, such as algae, the broodstock was found to have gradually enlarged belly and ovulation phenomenon.
With the development of the milkfish aquaculture industry, relying solely on the capture of seed in natural sea areas, it is often impossible to meet production needs. In order to solve the needs of aquaculture production seedlings, Hawaii, Southeast Asia Fisheries Development Center (located in the Philippines) and Taiwan Province of China In other regions, research on the artificial propagation of milkfish was carried out and preliminary successes were achieved, laying the foundation for artificial humanized production of fry.
Natural fish fry in the capture of natural fish fry catch (a) the characteristics of fry morphological characteristics of fry fish farming currently rely on natural sea catch, should first "understand the morphological characteristics of fry in order to be targeted The fish caught on the beach are generally absorbed by the umbilical cysts, and the morphology and size of the fry are also slightly different due to the different collection sites. Visual observations indicate that the fry are almost colorless and transparent. There are two large, dark black eyes and a group of black spots in the center. There are dense melanin clusters behind the eyes of the head, back, dorsal fin base and base of the caudal fin. Commonly known as the “three-point flowerâ€, this is to identify the juveniles of juveniles. One of the characteristics of the fish is that under the dissection microscope, close to the top of the pectoral fin, there is a pronounced splayed radial plume below and a shiny, stellate melanin on the abdominal wall (Figure 2-16). Experienced fishermen identified the milkfish fry with a look at the fish’s unique body colour and swimming habits.
(2) The time and place of fishing, and the time of emergence of fry in the natural sea area are subject to environmental factors such as water temperature, and are slightly different depending on the region. The south is earlier than the north. Fry seedlings appear once or twice a year. The sea area of ​​Hainan Province began to see seedlings after the Ching Ming Festival and was seen from May to September, but there were fewer fry after October. There are more catches before and after the Lunar New Year 15 and less at the beginning and end of the month. Since newly hatched juveniles and juveniles are not yet fully developed and have no ability to swim or swim, and are similar to plankton drifting along with water, the distribution on the shore is affected by wind and currents. In general, the waves and estuaries near the spawning ground at high tide, mangrove swamps and bays, and Hong Kong forks are sites for fishing.
(iii) Fishing Tools and Methods The main gear and fishing methods for catching the shielded fry are:
Bazi-setting network: also known as the trapping network, you can choose the brackish water estuary, Xiaogang Bay and the mangrove swamp area of ​​the Gap crossing and the coastal shore waves, near the edge of the 30 to 40 degrees to bamboo, etc., to form a figure eight frame, The mouth of the network should face the trend, leaving a gap of 0. 8m wide at the angles, and attach the nylon mesh bag and the seedling collection box (fig. 2-17), and use the long strip of freshwater catch fry: About 3 to 5 meters wide and 1.2 to 1,5 meters dense nylon mesh cloth, both ends of a small bamboo basket to wear. The operation of the two is equivalent to a small net lift. At the high tide, the juveniles are caught in the rolling waves on the shore and deep in the chest.
Triangular hand operation net: Take larvae and juvenile fishes on the shore wave during the day.
Trapezoidal hand pushing net: The bamboo is used as a shelf, which is made of polyethylene or nylon mesh cloth, so that it floats on the surface of the water, the mouth is wide and the rear end is narrow, and it looks like a geometric trapezoid.
Small trawls: The nets are hung on the starboard and sideboards of boats or sampans, with the net mouth facing forward, and the seedlings are towed on the surface of the water. The towing speed should be maintained at a stable speed exceeding 20-40% (30-40 cm/s) of the maximum swimming speed of juveniles, not only to prevent fry damage, but also to increase the amount of catching insects.
Regardless of the type of fry collected, the other types of creatures in the mix must be removed. The method is: the fish caught in a 2-3L container, add mixed water (10 freshwater plus 1 serving of seawater), so that the salinity adjusted to 3-4 ‰, milkfish can adapt to sudden changes in salinity , but mantis shrimp and other non-essential creatures die due to inadaptability. Some fish can be removed by hand, but it is difficult to completely remove some predatory fish.
The cultivation of milkfish in milkfish is mainly in the form of saltwater pond cultivation and lakes and bays. The former is the main one.
(A) Breeding facilities Aquaculture ponds should be built at an average annual water temperature of 15. Beaches and mangrove swamps at °C. And there is sufficient fresh water in the sea and the transportation is convenient. The pool bottom elevation should generally be 10-15cm higher than the local minimum tide level. The bottom of the tank should be flat and be inclined toward one end of the drain. There should be a proper amount of fertilizer layer at the bottom of the pool to facilitate the breeding of basic bait. The elevation of the embankment may be 50cm higher than the high tide or high tide line, and the embankment is preferably made of masonry and 65cm high.
According to the characteristics of milkfish can be divided into three types of breeding ponds.
1. The fish fry storage pool is used for raising and catching fry for catching and returning. Smaller area, more than 10 acres. The water depth is generally 15-30cm to facilitate the growth and reproduction of algae, and provide a rich basic bait for fry.
2. The area of ​​aquaculture ponds should be 15 to 30 acres, with a maximum of 100 acres. The water depth is generally 35-100cm, and 1 to 2 gates are set. The rearing pond is used to rear fish and adult fish.
3. The wintering pond has a small area and can be built around a corner of the rearing pond. The pool can be digged with a 2-3m deep ditch, and a grass shed can be built on top and a wind wall can be built behind.
(II) After the ponds are cleaned and inflows are generally harvested, they will be imported into the wintering ponds in the future and the aquaculture ponds will be cleared. Before the spring floods, the drug clears the pool again. To disinfect and disinfect. After the fish ponds in the Qingchi Pond, after the basal fertilizers are applied, the water can be filtered through the nets, so that the basic baits can be properly propagated in preparation for laying seedlings.
(3) Seedlings of fish caught in April to May are generally 12 to 16 mm in length and the fish body is transparent and colorless. It needs to be kept in the fry storage pool for 4 to 5 weeks. After the fish grows, it will be raised in the rearing pool. The rearing ponds can be mainly supplied with large-size over-wintering fish species, but they can also be used in conjunction with part of the fish species in the current year, and the stocking density can be reasonably determined according to the pond's load capacity and the fish specifications of the listed products. Large areas of farming are mostly extensive culture, while small areas of culture are mainly semi-intensive, and they are mostly polyculture. Milkfish can be either polycultured with saltwater fish or mixed with freshwater fish. When stocking alone, it can stock 600-1, 000 or even more. Polyculture can store 400-500 mu per mu while stocking 600-1000 shrimps. If the pond algae thrive, incorporate feeding and fertilization, the conditions for changing the water are good, and the amount of fish stocks can be increased.
In addition to polyculture of fish and wintering fish in the same year, fish of different specifications in the same year can also be polycultured, for example, 200 seeds of 5cm body length can be stocked per mu, and 120 to 150 seeds of 15cm and 18cm seedlings. Gradually sparse feeding is adopted for catching up with large populations. Generally, the yield is relatively high, and the average annual yield can reach 130-200 kg.
(IV) Feeding Management
1. In addition to fertilizing the basal fertiliser before transplanting, the fertilizer should be applied in a suitable amount at the right time in accordance with the fatness of the pool water.
Top dressing is mainly applied to chicken manure, pig manure and a small amount of cow dung, human feces and other organic fertilizers, combined with some chemical fertilizers such as urea. Fertilizer should be timely, fertilizer should be based on changes in pond water color and the density of fish to master. General organic fertilizer such as chicken and pig manure is 20- 25kg per mu and 0,75kg urea. Before topdressing, the fish in the pool can be concentrated in the deep water of the pool, generally concentrated in the wintering pool, and then the water in the pool can be drained. The whole pool can evacuate the fertilizer evenly, and then add a small amount of seawater to make the fertilizer soaked. Add water to normal water several times. Can also be drained, directly fertilize in the pool, but to avoid the bait together. When the water salinity is too high, or when it is rainy or hot, it should not be applied.
2. Feeding If the density of the rearing fish in the pond is high, it is difficult to meet the needs of the fish to feed by fertilizing the cultured bait alone, artificial bait should be fed to the pond regularly to supplement the deficiency of the natural bait. Artificial feed is rice bran, peanut cake, bean cake, corn flour, etc., and it is better to mix and feed. The daily feeding amount is generally 3% of the total weight of the fish body. And according to the weather, water temperature, water color and actual feeding conditions, continue to adjust. After 8 o'clock in the morning or around 3 o'clock in the afternoon, the bait is evenly spread on the surface of the pond to allow fish to feed freely.
3. The water quality regulation pool water should maintain a certain water level, and according to the main water quality factors such as water color, transparency, dissolved oxygen, etc., water should be added and changed in a timely manner.
The salinity of milkfish in pond culture is 16-32‰. Production practices have demonstrated that the pond production is highest in the range of 20 to 22 degrees of salt. Conditions can be adjusted by sea and fresh water so that salinity can be maintained in this range.
4. The patrol pool must adhere to a daily patrol pool to observe the status of water quality, the water's fatness, and the fish's activity. Pay attention to whether there are floating heads, dead fish, diseases, etc., whether there are breaches, leaks, or hidden dangers of fish escape. Once discovered, appropriate measures should be taken at any time to prevent problems.
5. The predators in the anti-fouling fish ponds are mainly harmful fish, such as loggerheads. Tilapia and so on. A scorpion fish with a body length of S to 10 cm can eater 4 to 4 tailfish fry every day; when tilapia grows large in the pond. Not only battling, fighting for oxygen. The space was occupied, and due to frequent digging nests to lay eggs, the bottom algae beds were destroyed and the growth and reproduction of benthic algae were affected. Therefore, it is necessary to clear the pool, select the good seedlings, and prevent the flooding of the gate inlet network. Once it is found that harmful fish enter the pool, it should be removed in time by methods such as net hunting and hook fishing.
Followed by chironomid larvae, polychaetes, snails, etc., of which the largest damage to Chironomidae larvae, can be a large number of ingested benthic algae and organic debris, thus destroying the algae bed, reducing the pond fat. The method of elimination is the application of insecticidal drugs such as safrole and disulfiram, which completely kill the larvae and is harmless to milkfish. The massive growth of aquatic plants in the pond reduces the fatness of the pool water on the one hand, and affects the growth and reproduction of food organisms in the pond, and it also affects the activity of milkfish. Due to the large amount of oxygen consumed by the nighttime respiration of these aquatic plants, causing the fish to float and even cause death, it must be removed at any time. Pond clearing should be rooted.
(5) Overwintering of milkfish When the temperature of the pool water drops below 12°C, the food intake of milkfish is reduced significantly, and even the food is stopped, and it swims in the deep water area of ​​the pool. Afterwards, the milkfish rarely moves into the overwintering stage. The wintering of the milkfish is to bring the listed fish of the end of the year into the wintering pool and allow them to pass through the winter.
During the overwintering period of milkfish, the water temperature can be changed, and a small amount of feed with good nutrition and poor pollution can be found. Since milkfish swim more slowly in the deeper bottom of the pool and breathe slowly, it must be ensured that there is sufficient dissolved oxygen in the pool. In the case of high water temperatures on sunny days, some pool water may be properly drained to improve water quality conditions and ensure the safe wintering of milkfish.
(6) A type of cage culture in the captive breeding line, using polyethylene nets or bamboo curtains to enclose a small area of ​​water in a large body of water and put the fish species of the milkfish for breeding. No fertilizer, no bait, only the natural food in the water body. The position of the captive should be selected in the inner bay where winds and waves are calm, smooth and small, and the water level in the low tide period is not less than 2m. The water quality is clarified without pollution, the sediment quality is relatively flat, and the silt or clay sediment is not too thick. As well.
It is advisable to have a captive area of ​​tens of mu to several hundred mu. Within this range, it is better to use smaller ones. The size of fish species raised in captivity should be larger, generally 400-600 species of 12-15cm fish can be released per acre, and the survival rate of captivity generally reaches 75-80%. The harvesting method is to set 2-3 fish collection bags on the edge of the net. To retrieve fish into bags, or to use nets and gill nets.
(g) Harvesting of milkfish in the same year is about 5-6 months. Generally, the body length can reach 10 to 240 cm and the body weight can reach 30 to 250 g. Each year, the species is 500-1500g long, or even larger. Every year, the fish growth rate is greater than that of the year. Fish weighing 250-300g can be harvested one after another, especially ponds with large and small fish species. Fish that meet the market specifications should be caught in time. When the water temperature fell below 12°C, it would migrate into wintering ponds and continue to breed in the following year.
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