Detailed Explanation of Key Technical Points and Methods for Turbot Farming
Turbot, also known as southern flounder, Atlantic summer flounder, and American summer flounder, belongs to the class Osteichthyes, order Pleuronectiformes, suborder Pleuronectoidei, family Paralichthyidae, subfamily Paralichthyinae, genus Paralichthys. It is a deep-sea benthic fish and is the largest individual among the many flounder species in the Americas. Its natural distribution ranges from North Carolina to the southern Gulf of Florida in the United States, with populations also found along the southern straits of Texas.
The turbot's morphology is similar to that of China's olive flounder, with a laterally compressed, oval body, both eyes located on the left side of the head, and the left side of the body being light brown with irregular spots. The abdominal area is lighter in color and can change with the surrounding environment to conceal the body and evade predators. Turbot is a euryhaline fish and can typically survive in both seawater and freshwater. Females grow faster than males and can reach sexual maturity at two years of age. Males typically have a lifespan of two years; according to reports, the longest-lived males in South Carolina can reach over 3 years. At the same age, females are significantly heavier than males, and a three-year-old female adult can reach approximately 25 cm. In natural waters, adults can grow up to 75 cm. Females grow faster than males; at sexual maturity, two-year-old males can reach 20 cm to 25.5 cm, while females can reach 30 cm to 35.6 cm. Under artificial farming conditions, the growth period is significantly shortened, results are achieved more quickly, and benefits are greater. In natural waters, turbot has the ability to ambush prey. Larvae mainly feed on crustaceans, and as the fish continues to grow, they gradually feed on various fish species. Typical prey includes spotted mullet, striped mullet, white mullet, and grass shrimp.
Turbot has characteristics such as fast growth, superior quality, wide adaptability, and strong stress resistance, along with delicate meat and rich nutrition, making it a recognized excellent farmed fish. The United States began researching turbot breeding and farming techniques in the early 1990s and has made breakthroughs in physiology, ecology, artificial propagation, and farming technology. Turbot farming has become a rapidly developing emerging aquaculture industry in the United States. After this species was introduced to China, it has shown great development value and broad prospects.
Turbot Farming
1. Selection of Fry and Seed Stock
(1) Size: Turbot and olive flounder are relatively similar in farming techniques and are easy to manage in production. Generally, when the fry grow to over 5 cm, they can be stocked in large ponds. Stocking is best when the size is over 8 cm, as the fry's constitution is stronger, disease resistance is improved, adaptability after stocking is greater, and the survival rate is easier to improve.
(2) Fry selection: When purchasing fry, pay attention to selecting fish that have complete body shape, normal body color, no deformities, no albinism, no damage to fin rays, and swim swiftly. They should be uniform in size, free of disease, and have no parasites on the gills.
(3) Stocking time: For outdoor farming, stocking begins when the water temperature is above 18°C, preferably from April to May each year. If too early, the low water temperature makes it difficult for the fry to adapt and may even reduce the survival rate; if too late, it affects their growth into market-size fish that year.
(4) Stocking density: For pond farming, stock 500 to 800 fish per mu; for pond cage farming, stock 100 to 200 fish per 3 m × 3 m × 1.5 m cage; for sea cage farming, stock 300 to 400 fish per 3 m × 3 m × 3.5 m cage; for industrial greenhouse farming, stock about 20 fish per sq m.
2. Pond Selection
Existing shrimp ponds can be used with slight modifications for turbot farming. A water depth of about 1.5 m is required, with sufficient water supply, fresh and pollution-free water quality, and good water inlet and drainage facilities. Before stocking, pond bottom treatment must be carried out: dry the pond, remove sludge, loosen the pond bottom, and expose to weathering and sun for over 10 days. Fill with 30 cm to 50 cm of water and disinfect with bleaching powder. The effective chlorine content in the pond water should be above 10 ppm. For bleaching powder containing 25% to 30% chlorine, apply generally more than 40 g per cubic meter of water.
Grow-out Management
1. Water Quality and Water Exchange
The quality of farming water determines the success or failure of farming. Throughout the entire farming process, carefully observe changes in water temperature and water quality, and regularly measure water temperature, dissolved oxygen, salinity, pH, ammonia nitrogen, sulfide concentration, etc. For pond farming, water regulation can be controlled by adjusting the water exchange volume. The water exchange volume is directly proportional to the water temperature.
2. Feed Nutrition and Processing
Turbot is a carnivorous benthic fish. Mix vitamins and flour evenly, then mix with fish meal and yeast powder, then add fish oil and mix evenly. Add fresh miscellaneous fish and fresh miscellaneous shrimp (or crushed frozen fish and shrimp). Place all the above mixtures into a pelletizer and stir to make pelleted feed. The main raw materials for processing moist pelleted feed are Spanish mackerel, sardine, chub mackerel, noodlefish, scaled sardine, and other miscellaneous fish. Freshness must be good; those with poor freshness or excessively long freezing time cannot be used. During the farming process, vitamin C, vitamin E, and multivitamin complexes can be added to the feed to strengthen the fish's nutrition and prevent disease caused by nutritional deficiency. Note that processed feed should be fed on the same day, and any remainder should be properly frozen for storage. The maximum storage time must not exceed 2 days to prevent spoilage.
Commercial feed meeting nutritional requirements can be used. Note that when water temperature is low or high, the number of feedings and the amount fed can be appropriately reduced. In principle, there should be no residual feed, and no feeding should be done before medicated baths.
Turbot Disease Prevention and Treatment
1. Understanding the Causes of Fish Diseases
(1) Water temperature changes: Fish are poikilothermic animals and cannot regulate their body temperature. Their body temperature changes with the rise and fall of the ambient water temperature. Sudden changes in water temperature can cause fish death. Generally, when the body temperature fluctuation exceeds 2°C for larvae and juveniles or 5°C for adults, the fish are in a state of stress, and this is when they are most susceptible to death.
(2) Dissolved oxygen content in water: Fish have a relatively high oxygen consumption. The dissolved oxygen in the fish's living environment is often in a less-than-sufficient state, especially under high-density farming conditions, where oxygen deficiency frequently occurs, making fish prone to disease. Therefore, taking aeration measures according to actual conditions is very important. Suitable dissolved oxygen is generally 4 mg/L to 12 mg/L, with the most suitable being 8 mg/L to 9 mg/L.
(3) COD: Less than 3 mg/L. If ammonia nitrogen and COD levels in the water are too high, water quality deteriorates, and diseases are likely to occur.
(4) pH: 6.0 to 9.5 is suitable, with the optimal range being between 7 and 8.2. As long as regular observation and testing are carried out during the farming process, it is relatively easy to manage.
(5) Salinity and temperature: Strong environmental adaptability is a distinct advantage of turbot compared to other fish. Its suitable salinity range is 0 to 60, with the optimal being 5 to 35; it can even grow in freshwater. Its survival temperature range is 1°C to 35°C, and the suitable farming range is 18°C to 30°C.
(6) Feed: Fish also often suffer "illness entering through the mouth," so choosing the right feed is very important. In preparing live feed and compound feed, attention must be paid to both nutritional balance and freshness, while avoiding contamination during processing. Feed protein requirement is 32% to 48%, with the optimal being 38% to 48%. After 8 to 12 months of farming, fish generally reach about 600 g to 800 g.
2. Fish Disease Prevention Measures
(1) Stocking density: The stocking density of fry should be appropriate. Excessive stocking density increases the amount of feed and fish excrement, reduces dissolved oxygen, and deteriorates water quality.
(2) Water exchange volume and waste removal: As the fry grow, gradually increase the water exchange volume. Generally, for 5 to 10 days of age, exchange water once daily at 30% to 50%; for 11 to 20 days of age, exchange water twice daily at 40% to 60%; for 20 to 30 days of age, exchange water twice daily at 50% to 70%. Siphon waste once every 1 to 2 days. Ponds should have their bottom sludge cleared annually, and indoor concrete tanks should have their bottoms siphoned promptly to remove impurities.
(3) Filtration and purification: Water used for greenhouse farming must at least undergo sand filtration and purification. The fine sand for sand filtration should have a particle size of 0.15 mm to 0.25 mm and a thickness of about 60 cm.
(4) Strengthen feeding management: During the farming period, the nutritional requirements of larvae, juveniles, and adults must be met. Feed freshness must be good and nutrition complete. When necessary, add multivitamins, vitamin E, vitamin C, and minerals. Biological feed used for fry rearing must be rinsed clean with fresh seawater before feeding. If miscellaneous bacteria are present, antibiotic disinfection treatment must be applied. The number of daily feedings is determined according to the fish's needs. Feeding should be done with consistent quality, quantity, timing, and location. In principle, there should be no residual feed.
(5) Drug prevention and treatment
① Fish body disinfection: Purchased fry must undergo medicated baths regardless of whether they have diseases or injuries. After sorting and tank transfer during the fry rearing stage, medicated baths should also be carried out. Commonly used disinfectants include formalin, copper sulfate, ferrous sulfate, etc. Formalin at a concentration of 1×10-4 to 2×10-4 for a 60-minute to 120-minute bath can prevent bacterial and parasitic diseases; copper sulfate at 5×10-7 to 7×10-7 plus ferrous sulfate at 2×10-7 to 3×10-7 can prevent ciliates. Among drugs for preventing and treating turbot diseases, potassium permanganate must be strictly prohibited, because the respiratory system of Paralichthys species is very sensitive to potassium permanganate. There have been many cases of flounder death caused by the application of potassium permanganate.
② Pond disinfection: Regularly disinfect water bodies. The most commonly used method is splashing quicklime. For a pond 1 m deep, use 10 mg to 20 mg per mu, which can sterilize and improve water quality. In addition, bleaching powder at a concentration of 5×10-7 can be used for sterilization and disinfection.
Estimated Farming Benefits (Calculated at 200 yuan/kg)
1. Pond farming: Stock 500 to 800 fish per mu, with a survival rate of 80%. After 6 to 12 months of farming, the average weight reaches 0.5 kg to 0.8 kg per fish. Income per mu can reach 60,000 yuan to 100,000 yuan.
2. Pond cage farming: Stock 100 to 200 fish per 3 m × 3 m × 1.5 m cage, with a survival rate of 80%. After 6 to 12 months of farming, the average weight reaches 0.5 kg to 0.7 kg per fish. Income is 8,000 yuan to 20,000 yuan.
3. Sea cage farming: Stock 300 to 400 fish per 3 m × 3 m × 3.5 m cage, with a survival rate of 80%. After 6 to 12 months of farming, the average weight reaches 0.5 kg to 0.7 kg per fish. Income is 20,000 yuan to 40,000 yuan.
4. Industrial greenhouse farming: Stock 20 fish per sq m, with a survival rate of 80%. After 6 to 12 months of farming, the weight reaches 0.5 kg to 0.8 kg per fish. Income is 1,600 yuan per sq m to 2,500 yuan per sq m.