preface
The wild cross-banded bream, also known as the red bream, belongs to the family Snapidae, a fish with a unique appearance and ecological characteristics, being a medium-sized fish with an average body length of up to 30 cm. Its body is oval in shape, dark red on the back and pale silvery white on the belly. The most striking feature is that it has a distinct transverse band on the side of the body that extends from the head to the tail. These transverse bands usually appear bright red or orange.
However, due to the scarcity of wild resources, there is no obvious peak fishing period for cross-banded seabream, so its catch is relatively low, and the market demand is in short supply. To overcome these problems, wild immature individuals under 2 years of age caught by shrimp trawlers can be collected and cultured in captivity until sexual maturity is reached.
During the wintering period, broodstock are intensively bred to obtain sufficient and high-quality breeding broodstock, which increases the survival rate of domestication, obtains farmed broodstock earlier in the life cycle, and reduces dependence on mature broodstock.
Through the artificial breeding and intensive breeding of wild immature individuals, the number of breeding broodstock of the cross-banded seabream has been effectively increased, and the survival rate of domestication has been increased, which will help meet the market demand for this fish and promote its large-scale artificial breeding.
Domestication of wild cross-banded bream
In order to ensure the health of the fish, oxygenated bags are used to ensure that the fish reach the cement tanks of the breeding site quickly and safely.
Before the fish are transported, effective disinfection is carried out, the fish are soaked and disinfected for 10 minutes using 40 mL/m3 of formaldehyde freshwater solution to ensure that any potential pathogens are eliminated, and the breeding pond is covered with a black shade net, covering 50% of the pond area to reduce light intensity and environmental stimuli, creating a relatively quiet breeding environment.
The fish pause their feeding for 1 day when they first arrive, which helps them adapt to their new environment, and from day 2 onwards, a small number of frequent baiting methods are used. A small amount of fresh Kudzu gibbon is used for feeding first, and the feeding amount is gradually increased to promote the appetite and adaptability of the fish.
Once the fish's feeding behavior becomes normal, artificial compound feeds are gradually introduced and vitamin C is regularly added to the feed to improve their immunity and overall health.
In order to stimulate the feeding response of the fish, a sound is made by gently tapping on the wall of the breeding pond during feeding. This sound stimulus helps increase the fish's appetite and concentration, making them more active in feeding. In order to maintain the cleanliness and hygiene of aquaculture waters, bait residues and contaminants are regularly removed to avoid the risk of deterioration of water quality and disease transmission.
It is also necessary to pay close attention to the feeding and activities of broodstock fish, as well as any potential health problems, and once a sick fish infected by injury is found, it will be immediately fished out and cultured in isolation to avoid the occurrence of diseases.
Broodstock breeding
The broodstock pond uses a circular flow tank with a diameter of 3.5 meters and a depth of 1.2 meters. There are 6 oxygenating stones evenly distributed at the bottom of the pond, simulating the artificial reef environment inhabited by broodstock, and 6 white PVC drainage pipes are fixed at the bottom of the pond, with a length of 30 cm and an inner wall diameter of 25 cm.
For daily micro-flow water treatment and to simulate broodstock habitats, these drains are inserted near the drain at the bottom of the pond, which also has a smooth leak 1.2 meters from the bottom of the pool.
When broodstock reach maturity and their gonads begin to develop, the broodstock in domesticated ponds are usually 3 years old and weigh more than 200 grams. After a medicinal bath with a 30 ml/m³ freshwater solution of formaldehyde, the broodstock are placed in broodstock breeding tanks.
Each nursery pond is stocked with 150 broodstock fish, with a male-to-female stocking ratio of 2:1. The water temperature should be kept above 18 °C and the dissolved oxygen concentration (ρ) should be kept above 5 mg/l. 300% water exchange is carried out every day, and ammonia nitrogen is monitored regularly to ensure stable water quality.
Broodstock are fed mussel meat and fresh kudzu gibbon in daily feeding. At the same time, the daily feeding amount includes 1%~2% of the body mass of the fish. The feeding amount in the morning accounts for 40% of the total daily feeding, the feeding amount in the evening accounts for 60%, and 2%~4% vitamin C, 1%~2% vitamin E and 6%~8% immune polysaccharides are added.
Feeding times are 7 a.m. and 5 p.m. respectively. In order to record aquaculture production, detailed aquaculture production records are required on a daily basis. Every 15 days, the broodstock need to be poured into ponds, and the broodstock are soaked in 30 ml/m³ formaldehyde freshwater solution in batches for 10 minutes, and then quickly transferred to new breeding tanks, which can effectively prevent the occurrence of parasitic diseases. During broodstock breeding, it is necessary to stop pouring the pond and carry out medicinal bath disinfection treatment to avoid affecting the natural spawning process of broodstock.
Cross-banded seabream overwintering
1. Regulation of water temperature
In the wintering stage, in order to ensure that the water temperature in the aquaculture pond is suitable, when the natural sea water temperature is lower than 18 °C, it is necessary to warm the aquaculture sand filter water in advance, and adjust its temperature to 18~22 °C for daily water change, such a heating step can prevent fish from being affected by excessive cold, which is conducive to their growth and health.
Also in the breeding tank, a heating rod with a power of 2000 watts is placed and equipped with a thermostat to maintain a constant temperature, setting the temperature at 18 ° C to ensure that the water temperature in the breeding tank is always stable, which not only provides a warm and comfortable environment for the fish, but also supports their metabolism and the normal functioning of the immune system.
During the breeding season, it is necessary to regularly observe the changes in the body shape of broodstock in order to accurately judge their reproductive status. Once the abdomen of individual females begins to bulge, this is usually a sign that they are ready to spawn. In order to promote the spawning process, the water temperature is increased by 1°C month by month until the ideal temperature for broodstock to spawn is reached 22°C, and the temperature is kept stable, which helps to stimulate the reproductive behavior of broodstock and improve the reproductive success rate.
2. Regulation of water flow
A submersible pump with a power of 20 watts is fixed at the bottom of the pool wall, and the outlet is set at a horizontal angle of 30° to the tangent of the pool wall, 40 cm from the water surface. From four months before the breeding period, the water flow at the outlet is set at 800 liters per hour, and when the abdomen of individual females is raised, the water flow is adjusted to 1200 liters per hour.
It is also necessary to continuously stimulate the water flow for 12 hours a day, thus creating different water velocities around the fish pond. In this way, the broodstock will swim against the current to stimulate their gonadal development, increase their movement, and lay a solid foundation for the arrival of the breeding period.
Most importantly, the circulation along the wall of the pond can also collect dirt in the center of the pond floor, which is conducive to the cleaning of the breeding pond. This circulation design can effectively improve the quality of the breeding environment, reduce the dispersion of pollutants, and maintain the cleanliness and transparency of the water body.
3. Regulation of light
When the natural water temperature drops to 18°C, four 200-watt incandescent lamps are installed 1.2 meters above the breeding pond to ensure uniform light. At the same time, the light intensity should also be adjusted to ensure that the light intensity everywhere on the water surface reaches 500lx, in order to effectively block the outside light and insulate, the surrounding area of the breeding pond is fenced, and black curtains are used as shading materials.
The following light time management scheme was adopted: the initial light time was 12 hours, then 20 minutes of light time was increased every three days until the light time reached 16 hours, and this time was maintained, and the light conditions in the breeding pond were always just right by precisely controlling the light time each day using timers.
4. Feeding requirements
When the water temperature drops to 18°C, feeding is performed once a day at 7:00 am and 5:00 pm. At this time, the fish are fed mussel meat and fresh kudzu gibbon, with some beneficial and detailed ingredients. In order to improve the immunity of fish, vitamin C accounting for 2%~4% of the total feed amount, vitamin E of 1%~2% and immune polysaccharides of 5%~6% will be added. The feeding amount will account for 1%~2% of the body mass of fish.
Specifically, morning feeding accounted for 40% of the day's feeding, while evening feeding accounted for 60%. When individual females begin to bulge in their abdomen, they are given some special feeding. Every day at 7:00 a.m. and 5:00 p.m., they are fed mussel meat, oyster meat and silkworm meat.
Some ingredients should be added to meet their needs, including vitamin C accounting for 2%~4% of the total feed amount, vitamin E of 1%~2%, lecithin of 0.2% and immune polysaccharides of 5%~6%. At this time, the feeding volume will account for 3% of the body mass of the fish to ensure optimal growth and health of the fish.
5. Clean water quality
When rearing juvenile wild bream fry, clean and pollution-free sources should be selected, such as groundwater or pretreated tap water. Parameters such as temperature, pH and dissolved oxygen of water quality should be appropriate to meet the growth needs of fish.
During the aquaculture process, water quality should be monitored regularly to ensure that it is in a suitable state, and routine monitoring items include indicators such as water temperature, pH, dissolved oxygen, ammonia nitrogen and nitrite, which can be done by using professional water quality testing equipment.
Juvenile wild bream fry have high water temperature requirements, usually between 18°C and 25°C. In winter, especially in cold areas, measures need to be taken to keep the water temperature stable, such as using heating equipment or setting up greenhouses.
The pH of water quality is also important for fish growth and health, and the suitable pH range for juvenile wild cross-banded bream fry is generally 6.5 to 8.0. If the water quality is acidic or alkaline, it can be adjusted by adding chemicals such as lime or ammonium sulfate.
It is also necessary to maintain a good supply of water oxygen during the culture process to ensure that fish receive enough oxygen, which can be achieved by increasing surface oxygen exchange, adding aeration devices or increasing water flow.
Ammonia nitrogen and nitrite in water quality are common harmful substances, ammonia nitrogen mainly comes from fish metabolism and feed residues, and nitrite is the product of ammonia nitrogen oxidation by bacteria in water, they have a negative impact on fish health, so it is necessary to reasonably control the content of ammonia nitrogen and nitrite in water quality, which is very important for the culture of juvenile wild cross-banded bream fry.
Author's point of view
In order to obtain sufficient and high-quality breeding broodstock, it is necessary to carry out intensive breeding of broodstock during the wintering period, improve the survival rate and reduce the occurrence of fish ulceration disease in the domestication stage of broodstock, regular medicinal bath disinfection treatment and early increase of water temperature are important measures, significantly improving their survival rate.
In the broodstock breeding pond, the wild environment is also simulated, and artificial fishing reefs are put into place, providing a more suitable living environment and helping broodstock better adapt to the artificial breeding environment.
In addition, during the wintering period, attention is paid to providing the right environment and nutrients for broodstock to promote the natural development and maturation of their gonads, thereby increasing their spawning capacity, including providing suitable water temperature, nutrients and other necessary conditions to ensure that the broodstock gonads are fully developed, thereby increasing the success rate of reproduction.
Through these improvements, better results can be achieved in shrimp trawler culture, the quality of cultivation of wild immature individuals can be improved, and the reproductive capacity of broodstock can be maximized.
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