Detailed Explanation of High-Yield Artificial Farming Techniques for Sea Bass

Sea bass, also known as Japanese sea bass or seven-star bass, belongs taxonomically to the order Perciformes and the family Moronidae. Because it breeds and grows in coastal waters, unlike the freshwater largemouth bass and mandarin fish, it is also called sea bass. The sea bass is a fierce carnivorous fish that naturally feeds on small fish and shrimp; in artificial farming, it mainly eats high-grade extruded feed with a small amount of small fish. The sea bass is a euryhaline fish with characteristics such as fast growth, wide adaptability, and strong disease resistance. The farming techniques are described below.

Pond Requirements and Preparation for Stocking Fry

1. Pond. Each pond should preferably have an area of 8 to 12 mu and a water depth of about 2 m. If the pond is too small, the water body is narrow and dissolved oxygen is insufficient, making high yield difficult; if the pond is too large and too deep, production operations are inconvenient. The pond should preferably be provided with inlet and outlet sluice gates, leading respectively to inlet and outlet rivers, and the farming water should not be reused, so as to avoid secondary pollution.

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

3. Pond clearing. Ponds used for farming sea bass must undergo drying, dredging, and sun exposure, especially old ponds that have been used for many years. Half a month before stocking fry, disinfect once, applying 150 jin of quicklime per mu or using 20 mg/L 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 entire 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 fertilization. After disinfection, filter fresh water into the pond (about 80 cm), and apply some compound fertilizer to cultivate plankton.

Fry Selection and Rearing

1. Fry selection. The stocking 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 holding in net cages for sale, generally at a size of 2 to 3 cm. When selecting fry, pay attention to uniformity and do not necessarily seek large size. Also pay attention to “black body” fry; such fry have a low survival rate due to transport stress.

2. Fry stocking. The general stocking density is about 8,000 fry per mu. Stocking is generally carried out at noon on a sunny day (at this time water temperature and dissolved oxygen are relatively high, which can reduce discomfort to the fry). After disinfection with water, the fry are placed into the prepared grid. Because high-density farming involves heavy feeding, and sea bass rarely seek leftover feed at the pond bottom, after removing the net, 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 rearing. After stocking, turn on aeration fully (preferably bottom aeration with air stones). Generally no feed is given on the first day. After one day, gradually begin feeding and training to eat, requiring fixed locations and fixed times, generally four meals. The best opening feed is water fleas, but fish paste mixed with part of eel feed can also be used as opening feed. When the fry reach 5 to 6 cm, extruded feed can gradually be given. During the fry stage, feed should be appropriately supplemented with drugs for preventing enteritis. As the fry gradually grow, the grids should be gradually removed.

Management and Disease Control

1. Daily management

(1) Feeding: Sea bass are prone to overeating, 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 carried out at fixed locations, fixed times, and fixed amounts, generally 2 meals per day, respectively at 6 to 7 in the morning and 6 to 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 observing the fish school's feeding and health status, so that responsive measures can be taken in time.

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

① Change water frequently, especially in the middle and later stages;

② Aerate frequently. During the fry stage, the aerator can be turned on appropriately. As the fish grow, the frequency of turning on the aerator should increase. Especially in high-temperature weather and in the later stage of farming, all aerators should be turned on to maintain sufficient dissolved oxygen in the pond water;

③ Apply biological agents. High-density farming brings large amounts of leftover feed and excrement at the pond bottom. The decomposition concentration of harmful substances is high, consuming large amounts of oxygen in the water, especially seriously in high-temperature weather. Appropriate application of biological agents can effectively degrade ammonia nitrogen and nitrite and maintain good water quality. This point is most easily overlooked by farmers.

④ Do a good job of disinfection and insect removal. Generally disinfect once every 15 days; the frequency depends on the fish's feeding condition.

(3) Pond patrol: 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. Also inspect whether any fish are swimming at the surface. Before a large disease outbreak, generally a few fish swim at the surface; this is the best and key period for diagnosis and medication. At night, especially from 2 to 3 in the latter half of the night, inspect the operation of the aerators.

(4) Anti-theft: Fish theft incidents occur every year, so anti-theft measures must be taken in the middle and later stages of farming. The general methods are to maintain sufficient lighting at the pond at night and set up fences around the pond; if conditions permit, monitoring equipment can be installed.

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 death. Main symptoms: gill filaments dark red, reduced feeding. Control methods: apply flocculants to absorb ammonia nitrogen in the water, apply substrate 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. Before disease onset, pay attention to prevention with biological agents.

(2) Enteritis. Diseased fish have a swollen abdomen and red and swollen anus; pressing the abdomen causes pale yellow mucus to flow out. The main cause is feeding spoiled feed or overfeeding. For treatment, first reduce feed (preferably skip one meal), and feed with broad-spectrum antibacterial drugs mixed into bait for 3 to 5 days, which generally can achieve recovery.

(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 into bait and fed continuously for 6 days. At the same time, splash the pond with strong chlorine preparation over the whole pond once per day for 3 consecutive days.

(4) Saprolegniasis. This disease mostly occurs in winter and spring when water temperature is relatively low. Grayish-white cotton-like mycelia attach to wounds on the body surface of diseased fish; the fish body is weak and gradually dies. After infection, this disease spreads relatively quickly. For prevention, part of the groundwater can be pumped in to maintain salinity, and more water can be added to maintain water temperature. This disease easily occurs under specific environmental conditions. Changing the pond water environment and maintaining sufficient nutrition in the fish body to improve disease resistance are the most effective control measures.

(5) Trichodiniasis, chilodonelliasis, and vorticellosis: These mostly occur on the body surface and gill filaments of fish during the intermediate rearing 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 to 1 mg/L can be evenly splashed over the whole pond, or formalin at 20 to 25 mg/L can be splashed over the whole pond. Parasites generally easily cause secondary bacterial infections, so disinfection is generally required after insect removal.

(6) Hepatobiliary syndrome: The main manifestations are reduced feeding, and gradually some fish swim at the surface and unexplained deaths occur. The main causes are frequent drug application 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 the liver to be overloaded for a long time, resulting in metabolic imbalance or even metabolic disorder. Prevention and control mainly involve properly regulating the water environment, scientific feeding, and regularly feeding Chinese herbal medicines for soothing the liver and promoting bile secretion mixed into feed, which has a certain preventive effect.

Current Farming Misconceptions

Some farmers mistakenly believe that “the more feed put in, the more fish produced,” not knowing that overfeeding leads to a decline in feed digestion and absorption rate, and over the long term may even cause disease, so excessive feeding causes waste. We suggest that farmer friends who use extruded feed must control it to preferably 70% to 80% full (the fish's feeding speed noticeably slows, and 70% to 80% of the fish only compete without eating). We might as well calculate: generally, one pond of new fish yields 28,000 jin, uses 1,000 bags of feed (20 kg per bag), and is farmed for 10 months. If the farmer feeds 10 jin more feed per day, the result will be as follows:

1. Feed conversion coefficient under normal feeding: 28 jin per bag;

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

3. Waste: 140×60=8,400 yuan.

In short, only by selecting good fry, regulating water well, using good feed, and preventing diseases well can healthy sea bass farming raise good fish and make money.