Choose good water quality, smooth tides, smooth water flow, moderate flow rate, avoiding wind and waves, no pollution of the bay to set up nets, the flow rate of the tide for 5cm/s ~ 15cm / s, dissolved oxygen 5ml / l is appropriate. The optimal water temperature for the growth of seabream feeding is 18-28℃, the appetite decreases below 15℃, basically no feeding below 10℃, and the seabream will die gradually below 6℃. When the water temperature is lower than 12℃ in the northern sea area, it should be moved indoors to warm up for the winter. The sea bream prefers higher salinity and water transparency in the sea area. The water depth should be more than 7m at low tide. It is necessary to choose the sea area with convenient bait supply and transportation and good security at sea as much as possible. A good sea area is the first condition for the success of net-pen culture of real seabream. Therefore, before aquaculture, it is necessary to choose the aquaculture sea area on the basis of wind conditions, water depth, flow rate, water color, water temperature, transparency, specific gravity, PH value, pollution sources and other factors.
1. Wind conditions: must be able to withstand typhoons of more than 12 and their waves.
2. Water depth: in general, the aquaculture sea area of the depth of water than the wind box to try to double the depth of water, that is, 3 meters deep nets, the lowest tide level to have 6 meters of water depth, 5-meter-deep nets, the lowest tide level to have 9-10 meters of water depth, the depth of the net box is determined by the depth of water, there is no certain depth of water can not guarantee the normal color of the water and transparency.
3. The flow rate of the net box culture sea area is generally 5-15 cm / s, the most suitable flow rate of 6-8 cm / s. If there is no flow rate, the bottom is easy to silt. If there is no flow rate, the bottom is easy to silt residual bait and fish excreta, destroying the environment of the fish farm and insufficient oxygen, affecting the growth rate of fish. On the other hand, if the flow rate is too high, although there is enough oxygen, the energy consumption of fish is high, which will also affect the growth rate of fish. In addition, if the current is too high, the fish netting will be easily damaged and the safety coefficient will be low.
4. Water color. between 13-15.
5. Transparency: more than 1 meter. Poor transparency of fish nets are easy to attach mud and other debris, not conducive to the growth of fish.
6. Salinity: the true sea bream is a wide salt fish, there is no major flooding invasion of the No. District are able to adapt. The suitable salinity of culture is 17-30‰. When the salinity is lower than 16‰, it is unfavorable to the growth of the sea bream.
7. Water temperature: water temperature range between 9-32 ℃, the most suitable 20-28 ℃, below 13 ℃, the sea bream is basically in a dormant semi-dormant state.
8. pH: The pH value of seawater is an important factor that directly affects the physiological condition and growth and development of the seabream. The best requirement of PH value is 7.6-8.4, which is lower or higher than this range will affect its normal growth.
9. Dissolved Oxygen: Dissolved Oxygen in seawater should be kept above 4mg/liter. If the dissolved oxygen drops below 3.5 mg/liter, it will make the fish feel uncomfortable or stop feeding, and even appear floating head death. Mako is also known as red plate, Gala, and Wangshan fish. It is rich in nutrients, especially fresh flavor, colorful and beautiful, known as "sea chicken". Japanese people in the birthday and wedding used to use the sea bream banquet, in order to express the meaning of good luck, therefore, the sea bream in the Japanese market is very popular, the price per kilogram are up to 22 U.S. dollars, the product demand exceeds supply, every year from China and North Korea and other countries to import a large number of sea bream. Mako is also popular in Hong Kong, Macao, Mainland China and Southeast Asia. Artificial propagation of seabream seedling has been successful, and the feed is also very rich, which is very suitable to use the vast shallow sea in our province to carry out net-pen culture. Now the artificial breeding of seabream and net culture technology is introduced as follows:
Seedling production Seabream breeding seed production process is: parental fish breeding → egg harvesting → hatching → fish rearing → sea rearing. Parental feeding is dominated by floating netting. There are two ways of breeding: one is to catch natural fish from natural sea area, inject hormone and collect eggs artificially. The second is to make the gonads of the parents mature through artificial feeding, and fertilize the eggs naturally, so as to carry out large-scale seedling production. In land-based heated circulating pools, the parents can be made to spawn 1 to 2 months earlier. The quantity and quality of spawning of Mako is highly related to the bait for the parents. The feeding of the parents is based on artificial bait, frozen fish and shrimp meat. The minimum protein content of the bait should not be less than 50%. Parental fish in the land-based spawning pool (50 to 70 tons) in the natural spawning, spawning parents for 1 to 1.5 kg (tail fork length 35 to 42 cm) is more appropriate, each spawning pool parent density of 1 to 1.5 kg / m 3. Spawning season, if each spawning pool to host 1 kg of male and female parents of each 40 tails, each day can be obtained from 4 to 5 million fish. Under the specific gravity of 1.0213, fertilized eggs generally float in the middle and upper layers of water, while unfertilized and dead eggs sink. Fertilized eggs collection, is set up in the spawning pool outside a sieve silk fishing net (mesh diameter of 0.5 mm), floating fertilized eggs with the water from the outlet into the fishing net, counted for hatching. General use of indoor fiberglass tank (50 tons) static water aerated incubation. Fertilized eggs at a water temperature of 15.3 to 16.8 ℃, incubation time of 58 hours. Seedling cultivation is divided into two stages, using two methods: indoor tank nursery and floating net box nursery on the sea surface. First stage. After the fry come out of the membrane, the first to two days rely on the body of the yolk to supply nutrition, after the second day, the true seabream fry digestive system is sound, began to feed. The main baits are rotifers, larvae of the fungus worm and artificial matching bait. In the early stage of rearing, the feeding density of the young fish is 1.5~50,000 per cubic meter, and the survival rate is about 50% when they are raised to 10 millimeters (30 days old). Subsequently, the stocking density was reduced to 10-15,000 fishes/m3 in order to avoid the same kind of fish. the second stage of cultivation was carried out in the floating net box. After the fry come out of the membrane, after 40 days of cultivation, the body length can reach 15～20 mm, at this time, it can be moved from the land tank to the sea floating net box rearing. Siphon method can be used, with a diameter of 50 mm, 300 meters long hose, the fish fry from the land tanks into the floating net box, while counting the number of fish fry. The mesh of the small net box is 0.5 to 0.7 mm, the specification is usually 6 to 24 m 3, the stocking density is about 2000 fishes/m 3, and animal bait (with nutritional additives) and artificial bait are fed. The growth rate of fry varies greatly in different areas, and is related to environmental conditions and bait, especially the changes in water temperature have a greater impact on the growth rate of juvenile and adult fish. Large-scale intermediate brooding of juvenile fish. Construction of a natural nursery for juvenile fish, i.e., selecting a semi-enclosed inner bay and using a network of electrodes to intercept the mouth of the bay to form a natural net box. The juvenile fish are stocked in the waters of the inner bay surrounded by the electrode network and fed with automatic baiting machines four times a day. And according to the principle of conditioned reflex, acoustic domestication baiting, that is, set up a loudspeaker underwater, release a special frequency sound wave (50-200Hz), the fish can be heard within a radius of 1 kilometer, the baby fish hear the sound wave began to ingest, so as to achieve the use of acoustic management of the fishery. At the same time, automated management is carried out in the monitoring room on the shore using microcomputers. This intermediate cultivation method is more effective, which can fully utilize the natural productivity as a bait source, and the seedling is close to naturalization. Cultivation of biological bait. The bait for the early stage of the fry is mainly wrinkled brachyuran rotifers, the unsegmented larvae of Toyotomi and Japanese tiger fleas. At water temperature of 30-33°C, rotifers can produce cysts after 48 hours of incubation and it is easy to cultivate because of its high nutritional value. The nutritional value of rotifers depends on the content of unsaturated fatty acids. Cultivating rotifers with brewer's yeast only, rotifers lack unsaturated fatty acids. Cultivating rotifers with Chlorella is more effective. Generally 1 ton of seawater (each milliliter containing cells 500 ~ 1000 Chlorella) can cultivate 5 to 600 million rotifers, the need for static water aerated culture. In addition, the use of lactic acid bacteria, squid liver oil on the rotifers and the second nutrient-enhanced culture, culture for 1 hour, and then feed the rotifers to the true seabream fish, you can get the best growth rate.
Adult fish culture There are two ways to culture adult seabream, one is to culture in floating net box on the surface of the sea; the other is to build up a pool culture. At present, floating net tanks are commonly chosen for adult seabream culture. The specifications of floating nets are shown in the table.
Specifications of the net box
The mesh of the net box varies with the growth of the fish, such as raising up to 3 years of fish (1 to 1.5 kg), the mesh is about 14 to 50 mm. So prepare several types of nets. Stocking density is 7 to 10 kg per cubic meter. Bait and growth. It generally takes 1 to 2 years to raise commercial fish from 500 grams to 1 kilogram. Mainly feed frozen minced fish (raw bait) and with bait. If raw bait is fed, the meat gain coefficient is 11.3 during 16 months from fry to adult fish. it is determined that the meat gain coefficient of real seabream is different in different growth stages, 5.1 for the current year fish and 9.7 for 2-year-old fish. body color adjustment. In order to make the artificial breeding of real seabream body color peach bright, when sold to obtain a higher price, generally in the sale of 2 months before, in conjunction with the bait to add 1 to 2% of astaxanthin diester (purified from krill oil) feeding real seabream, or with Antarctic krill to add to the fishmeal bait, can prevent real seabream fish body discoloration. Shading the pool or netting with black polyethylene sheets to avoid direct sunlight can also prevent discoloration. Its basic structure is mainly composed of frame, float, net coat and sinker. Frame: Mostly wooden frame, generally made of planks about 8cm thick and 25cm wide connected with iron plates and screws to form a 3m×3m or 4m×4m combined conjoined frame, with 50cm×90cm foam floats (buoyancy 150kg) fixed on all sides. This kind of net box is suitable for the sea area with smooth wind and waves.
Nets: mostly made of chemical fiber materials, the shape of 3m × 3m × 4m and 4m × 4m × 4m with the frame to match the bottom of the nets by the rock or the bottom of the frame fixed formation. The mesh of the netting and the body length of the farmed fish points.
The growth temperature of real seabream is 17～28℃. feeding stops below 13℃. Generally speaking, the death of the water temperature is 5 to 8 ℃ below, in the static sea water, the water temperature slowly down to 5 ℃ will not die; if the sea water flow fast, the water temperature down to 7 ℃ or so, the true sea bream will die. If the water temperature drops to 7℃, the seabream will die. Above 29℃, the intake changes greatly, and physiological disorders are likely to occur. Therefore, it is better to overwinter in water temperature above 12℃.
The sea bream has a weak adaptability to low specific gravity seawater. When the specific gravity is below 1.020, the oxygen consumption of the fish decreases significantly and the feeding is not vigorous. A specific gravity of 1.020 or more is ideal for aquaculture. The relationship between oxygen consumption and seawater flow of real seabream, tail weight of 500 grams of real seabream hourly flow (dissolved oxygen 5 ml / liter) 10.7 liters, the safe flow of 15 liters.
The sea area suitable for sea bream culture must have the following conditions:
1. the depth of the water is generally more than two times the depth of the net box
2. the seawater flow is slow, and the exchange of tidal currents is smooth
3. the annual change of the water temperature in the range of 12-28 ℃
4. there is no large amount of freshwater injection, as well as the industrial sewage discharged into the
5. the sea is not affected by the platform and the rapids
5. the sea is not affected by the platform and the rapids, and the sea is not affected by the sea. Not affected by platforms and rapids
6. Convenient source of bait and convenient transportation of adult fish for sale
7. No influence of theft and shipping
8. No occurrence of red tide.
The relationship between the size of the fish and the mesh, stocking quantity is as follows: fish body 1 ~ 1.5 cm in length, mesh 1 ~ 2 mm (window screen), stocking quantity of 3,000 tails / cubic meter; the fish body more than 5 cm, mesh 1 cm, stocking quantity of 500 tails / cubic meter (mesh box specifications of 3 × 3 × 3 meters); weight more than 25 grams of stocking quantity of 6 ~ 8 kg / cubic meter in general (see table).
The bait for real seabream culture can be divided into fresh bait and artificial feed. Fresh bait commonly used are sardines, mackerel, mackerel, small stripers, yuzu fish and small mixed shrimps.
When using fresh bait, attention should be paid to the freshness. To prevent easy to cause nutritional diseases. The use of cold cross-frozen fish should be fully thawed, washing with seawater can accelerate the thawing, but also wash away the fat and dirt on the surface of frozen fish. Artificial bait has two categories: hard pellets and wet soft pellets. The common ingredients of commercially available hard pellet feeds are 45% crude protein, 3% crude fat, 15% crude ash, more than 1.8% calcium, 1.2% phosphorus, and a variety of vitamins.
The daily baiting rate of real seabream culture is directly related to the change of water temperature and fish size. The change of daily baiting rate mainly depends on the water temperature, followed by the difference of fish size. The baiting rate is expressed as the ratio of the daily baiting amount to the weight of the farmed fish. The baiting rate for juvenile fish weighing about 2 grams is 20%; the baiting rate in winter is 1 to 3%; for fish weighing more than 85 grams, the baiting rate is 5 to 8% in the moderate temperature period.
The true sea bream is an omnivorous fish, can be used in net box culture, 10 kilograms per cubic meter of water culture, feeding fresh mixed fish 1 to 2 times a day. The speed of baiting should be slow. Eat up and then cast, so as not to waste bait. Can also be used with artificial bait and fresh fish cross-feeding.
With the growth of the fish body, about 20 days to change the net, mesh gradually increase. Pay attention to the frequent washing and brushing of the net clothes, so as not to clog the mesh.