How to Raise Sea Bass Healthily? Master These Technical Key Points

Sea bass, also known as Japanese sea bass or seven-star bass, belongs taxonomically to the order Perciformes, family Lateolabracidae. Because it breeds and grows in coastal waters, unlike the largemouth bass and Mandarin bass that grow in freshwater, it is also called sea bass. Sea bass is a fierce carnivorous fish that naturally feeds on small fish and shrimp. In artificial breeding, high-grade extruded pellets are the main food, with a small amount of fry fish. Sea bass is a euryhaline fish with characteristics such as fast growth, wide adaptability and strong disease resistance. The healthy breeding techniques are introduced as follows.

I. Pond Requirements and Preparation for Releasing Fry

1. Pond. The area of each pond should be 8-12 mu with a water depth of about 2 m. If the pond is too small, the water body is narrow, dissolved oxygen is insufficient, and high yield is difficult to achieve; if the pond is too large and too deep, production operations are unfavorable. The pond should preferably have inlet and outlet sluice gates leading respectively to the inlet and outlet rivers, so that the aquaculture water is not reused, thereby avoiding secondary pollution.

2. Machinery configuration. One aerator should be equipped for every 1.2-1.5 mu of water surface; this is the basic condition for high-yield farming. The pond needs a water pump to ensure that new water can be replaced at any time, which is even more necessary for ponds without inlet and outlet sluice gates; in addition, a diesel generator should be equipped to prevent oxygen deficiency in the pond during power outages.

3. Pond clearing. Ponds used for raising sea bass must undergo drying, sludge removal and sun exposure, especially old ponds that have been used for many years. Half a month before releasing fry, disinfect once, applying 150 jin of quicklime per mu or using 20 ppm bleaching powder with an appropriate amount of pond water for disinfection. If the pond has not been dried and sun-exposed, tea seed cake should also be crushed, soaked in water and splashed over the whole pond to thoroughly eliminate wild and miscellaneous fish.

4. Net installation. Use fine nets to divide the pond into smaller sections to facilitate feeding of the fry.

5. Water cultivation. After disinfection, fresh water is introduced into the pond through a filter net (about 80 cm), and some compound fertilizer is applied to cultivate plankton.

II. Fry Selection and Cultivation

1. Fry selection. The fry release period is from early December each year to March of the following year. The fry needed for sea bass farming in Guangdong are basically hatched and desalinated in Fujian and then transported directly to Doumen, Zhuhai for temporary rearing in cages for sale, generally 2-3 cm in size. When selecting fry, pay attention to uniformity and do not necessarily go for large ones; also pay attention to “black body” fry, which have a low survival rate due to transport stress.

2. Fry stocking. The general stocking density is about 8,000 fry/mu. It is generally best to release fry at noon on a sunny day (at this time water temperature and dissolved oxygen are relatively high, which can reduce discomfort of the fry). After disinfection with water, the fry are placed into the prepared net pens. Because high-density farming involves heavy feeding, and sea bass rarely search for leftover feed at the pond bottom, after removing the nets, a small number of crucian carp, tilapia or bream (omnivorous) should be stocked per mu, together with a small number of bighead carp (filter-feeding), to reduce water pollution and increase farming benefits.

3. Fry cultivation. After releasing the fry, turn on aeration fully (preferably using air diffuser stones for bottom aeration). Generally no feed is given on the first day; after one day, feeding and feeding training begin gradually, requiring fixed locations and fixed times, generally four meals. The best initial feed is water fleas (Moina), or fish paste mixed with part of eel feed can also be used as the initial feed. When the fry reach 5-6 cm, extruded pellets can gradually be fed. During the fry stage, enteritis-prevention drugs should be appropriately added to the feed. As the fry gradually grow, the nets are gradually removed.

III. Management and Disease Control

1. Daily management

Feeding: Sea bass easily overeats, so the feeding amount should be properly controlled, which helps reduce costs, reduce the occurrence of gastrointestinal diseases and reduce water pollution. Feeding should be done at fixed locations, fixed times and fixed amounts, generally 2 meals a day, respectively at 6-7 in the morning and 6-7 in the evening. Generally a feeding bridge is built in the pond, and each meal should normally be fed until about 80% full. In case of high temperature or changing weather, the feeding amount should be appropriately reduced. Each feeding should be accompanied by observation of the fish school's feeding and health status so that responsive measures can be taken in time.

Water quality management: High-yield sea bass farming means high-density farming, so maintaining fresh water quality and sufficient dissolved oxygen is very important. The main methods are:

Change water frequently, especially in the middle and later stages;

Aerate frequently. During the fry stage, aerators can be turned on appropriately. As the fish grow, the frequency of turning on aerators increases, especially in high-temperature weather and in the later stage of farming, when all aerators should be turned on to maintain sufficient dissolved oxygen in the pond water;

Apply biological agents. High-density farming brings a large amount of residual feed and excrement at the pond bottom. The decomposition concentration of harmful substances is high and consumes a large amount of oxygen in the water, especially serious in high-temperature weather. Proper application of biological agents can effectively degrade ammonia nitrogen and nitrite and maintain good water quality. This point is most easily overlooked by farmers.

Do a good job in disinfection and insect removal. Generally disinfect once every 15 days, with frequency depending on the fish's feeding condition.

Pond inspection: During the day, mainly observe changes in feeding to judge the health status of sea bass. Generally, when fish are unwell, the first reaction appears in feeding. In addition, inspect whether any fish are swimming at the surface. Before a large outbreak of disease, generally a small number of fish swim at the surface. This is the best and also critical period for diagnosis and medication. At night, especially from 2-3 in the morning, inspect the operation of the aerators.

Anti-theft: Fish theft occurs every year, so anti-theft must be emphasized in the middle and later stages of farming. The usual methods are to keep sufficient lighting around the fish pond at night, set up fences around the pond, and install monitoring equipment if conditions permit.

2. Disease control

(1) Ammonia nitrogen and nitrite poisoning: In high-temperature weather, ammonia nitrogen in the water is high, and nitrite may even be produced, causing oxygen deficiency and poisoning in sea bass, reduced feeding and, in severe cases, dead fish. Main symptoms: gill filaments dark red, reduced feeding. Control methods: apply flocculants to adsorb ammonia nitrogen in the water, apply bottom sediment treatment agents to reduce ammonia nitrogen; release part of the old water and inject new water. When injecting water, avoid directly stirring up bottom sediment, which accelerates fish death; pay attention to preventive use of biological agents before the disease occurs.

(2) Enteritis disease: The abdomen of diseased fish is swollen, the anus is red and swollen, and pale yellow mucus flows out when the abdomen is pressed. The main cause is feeding spoiled feed or overfeeding. For treatment, first reduce the feed (preferably stop feeding for one meal), and feed broad-spectrum antibacterial drugs mixed with bait for 3-5 days, which generally can cure the disease.

(3) Hemorrhagic disease: The bases of the pectoral fins and dorsal fin of diseased fish are red and swollen and congested. Diseased fish move slowly and feeding decreases. This disease is caused by a virus and is highly contagious. For treatment, ribavirin and norfloxacin can be mixed with bait and fed continuously for 6 days. At the same time, the pond can be splashed throughout with strong chlorine powder once a day for 3 consecutive days.

(4) Saprolegniasis: This disease mostly occurs in winter and spring when water temperature is relatively low. Gray-white cotton-like mycelium attaches to wounds on the body surface of diseased fish. The fish body is weak and powerless and slowly dies. After infection, this disease spreads relatively quickly. For prevention, part of the groundwater can be pumped to maintain salinity, and more water can be added to maintain water temperature. This disease is likely to occur under specific environmental conditions. Changing the pond water environment and keeping the fish body nutritionally sufficient to improve disease resistance are the most effective control measures.

(5) Trichodiniasis, Chilodonelliasis and Epistylis disease: These mostly occur on the body surface and gill filaments of fish during the intermediate cultivation stage. Symptoms include emaciation, darkened body color, and erosion at the mouth end. They can occur in all four seasons. For prevention, water changes and water quality improvement are mostly used. For treatment, a mixture of copper sulfate and ferrous sulfate (5:2) at 0.77-1 ppm can be evenly splashed over the whole pond, or formalin at 20-25 ppm can be splashed over the whole pond. Parasites generally easily cause secondary bacterial infection, so disinfection is generally required after insect removal.

(6) Hepatobiliary syndrome: The main manifestations are reduced feeding, gradually some fish swimming at the surface and unexplained deaths. The main causes are frequent application of drugs under high-density farming, chronic accumulation of toxic and harmful substances in the fish body, leading to organ dysfunction and tissue damage; and long-term overfeeding, causing long-term overload of the fish liver leading to metabolic imbalance or even metabolic disorder. Prevention and control mainly involve regulating the water environment well, scientific feeding, and regularly feeding some liver-soothing and gallbladder-benefiting Chinese herbal medicines mixed with feed, which has a certain preventive effect.

IV. Current Breeding Misconceptions

Some farmers mistakenly believe that “the more feed, the more fish produced”, but do not know that overfeeding leads to a decline in feed digestion and absorption rate, and over time may even cause disease, so excessive feeding causes waste. We suggest that farmer friends using extruded pellets must control feeding to about 70% to 80% full (when the fish's feeding speed noticeably slows and 70%-80% of the fish only rush for food but do not eat). We might as well calculate: generally one pond of new fish yields 28,000 jin, uses 1,000 bags of feed (20 kg/bag), and is farmed for 10 months. If the user feeds 10 jin more feed per day, the result will be as follows:

Feed conversion coefficient under normal feeding: 28 jin/bag;

Feed conversion coefficient with extra feeding: 28000/(1000+0.25×30×8)=26.4 jin/bag;

Waste: 140×60=8400 yuan.

In short, only by selecting good fry, regulating water well, using good feed and preventing diseases well can sea bass be raised well and money be made in healthy sea bass farming.