Detailed Explanation of Key Sea Bass Farming Techniques and Management Methods
Sea bass is one of the common economic fish species and also a species developed for marine aquaculture. At the same time, sea bass is also one of the important economically valuable fish species that grows naturally. Artificial farming has a history of nearly twenty years. In recent years, driven by the market economy, sea bass farming techniques have made relatively major breakthroughs.
Pond Farming of Sea Bass
1. Pond conditions and preparatory work: The pond area should preferably be 3300 sq m-6600 sq m, with a water depth of more than 2 m, abundant water sources, non-polluted water quality, relatively good water inlet and drainage facilities, and convenient transportation. Before stocking, the pond needs to be dried, silt removed, and slopes leveled and protected. Use 750 kg-1050 kg of quicklime per hectare, maintain the pond water at 10-20 cm, and sprinkle it as a slurry. After 7 days, add water to a depth of 1 m. To keep the water quality in good condition, apply 75 kg/hm2 of diammonium once, and after two days, when the pond water turns oily green, stocking can begin.
2. Temporary rearing and stocking of fry: Sea bass fry are currently mostly caught at sea. In spring, sea-caught fry are about 2.5 cm-4 cm. After capture, transfer, and handling, the fish bodies will be injured to varying degrees. To improve the survival rate of farming, intermediate temporary rearing can be carried out first. For temporary rearing, it is relatively convenient to set up 40-mesh cages in the farming pond. Stock 2000-3000 fry per cubic meter of water, splash with 1×10-6-2×10-6 chloramphenicol for disinfection, and after they feed on minced fish, use furazolidone. In the first 10 days, feed brine shrimp larvae or marine and freshwater cladocerans and copepods, and then feed fresh minced fish. When the fry are cultivated to about 10 cm, stock them into the grow-out pond at 1.5 fish/m2.
3. Grow-out management
① Feeding: The bait is mainly low-value trash fish, supplemented by artificial compound feed. Sea bass grab food quickly and eat in large amounts, so feeding at fixed times and in fixed quantities is very important. When feeding, it is necessary to ensure the fish eat their fill without wasting bait. For each feeding, first feed a small amount to attract the fish to float up and compete for food, then increase the feeding amount. When the fish sink and no longer compete for food, stop feeding. The number of daily feedings and the feeding amount vary with the season. In the suitable temperature season for rapid growth of sea bass, feed 4-5 times per day, with the feeding amount at 10-30% of fish body weight. In the low-temperature periods of early spring and late autumn, feed 2-3 times per day, at 1-10% of fish body weight.
② Pond patrol inspection: Observe during morning and evening pond patrols, and handle any abnormalities promptly. The contents of pond patrol observation include fish activity, changes in pond water color, odor, and transparency, as well as pond escape-prevention facilities and predators.
Cage Farming of Sea Bass
1. Farming conditions: Good ventilation is required, water depth should remain more than 5 m at low tide, water flow should be unobstructed, preferably 0.3 m per second, the bottom should have no obstacles, water quality should be fresh and pollution-free, and salinity variation should be small.
2. Cage structure: Sea bass farming cages include the fixed pipe-frame type and the type with sandbags hung at the four corners of the net body. The fixed type uses metal pipes to make a frame slightly larger than the cage, and the cage is tied inside it to hold its shape. The sandbag type hangs a 4 kg sandbag at each of the four corners of the cage body to fix the net shape. In the south, wooden boards are mostly connected to make qualified fish rafts, which float on the water surface with buoyant balls and are positioned with anchor ropes, and cages are hung in the raft grids. In the north, single-net single-float frames are more common, and each floating cage is connected to positioning float ropes in the sea area. The opening size is usually 3×3 m and 4×4 m. The net depth depends on the water depth of the sea area at the time, generally 4-6 m. The mesh size depends on the fish body size. The principle for choosing mesh size is that even if one mesh is broken, the fish will not escape, and the mesh should be smaller than 1/2 of the fish body height.
3. Fry stocking: For sea bass to be raised to market size in the same year, the fry should first be temporarily reared to more than 10 cm before being counted and placed into cages. It is appropriate to stock 20-30 fish per cubic meter of cage water volume. The specific stocking density should also be determined according to fry specifications, seasonal timing, sea area conditions, bait reserves, and farming technique factors.
4. Feeding: The bait is mainly low-value trash fish, and pellet feed can also be fed. For each feeding, feed less first and then more. After attracting the fish to float up and compete for food, increase the feeding amount. The daily feeding amount should be based on eating their fill without waste, and feeding should stop when the fish no longer compete for food. Feed 4-5 times per day. In early spring and late autumn when water temperature is low, feed 2-3 times per day.
5. Daily management: Frequently wash and brush the net, and remove attachments, generally once every 10-15 days. Replace with new cages when necessary, frequently inspect cages, and strictly prevent escape and leakage. Pay attention to fish conditions, water conditions, and the occurrence of diseases.
Sea Bass Disease Prevention and Control
1. Eye opacity disease
[Symptoms] Mostly seen in the fry stage in spring and summer. White spots appear on the eyeball, gradually expand to cover the entire eyeball, and in severe cases the eyeball protrudes and falls off. This disease can be caused by stale bait and vitamin deficiency.
[Prevention and control] Renew the farming water body, feed fresh bait, and add vitamins to the bait (especially add VB).
2. Saprolegniasis
[Symptoms] Cotton-like bacteria appear on the fish body. Sick fish float to the water surface and swim slowly, have poor appetite, become emaciated, and die. Most cases are caused by infection after injury to the fish body.
[Prevention and control] Replace with new water, maintain good water quality, and bathe with 6×10-6 malachite green for 5-10 min.
3. Skin ulcer disease
[Symptoms] More commonly seen in high-temperature seasons. Local scale loss, congestion, and ulceration occur on the fish body. It is mostly caused by bacterial infection after injury to the fish body. Sick fish have poor appetite, float up and swim slowly, become emaciated, and die.
[Prevention and control] Bathe with 20×10-6 chloramphenicol (or furacilin) for 4 h-5 h.
4. Enteritis disease
[Symptoms] Sick fish have abdominal distension, red and swollen anus, yellow mucus flowing out, emaciation, poor appetite, and death in severe cases. It is caused by spoiled bait and high bait fat content.
[Prevention and control] Prepare furazolidone medicated bait at an addition rate of 0.1%, and feed continuously for 5-7 days.
5. Fish louse disease
[Symptoms] Fish lice parasitize on the fish body. Sick fish are restless, rub against the pond walls, and in severe cases the fish become emaciated and die.
[Prevention and control] Splash crystal trichlorfon over the whole pond so that the pond water reaches a drug concentration of 0.25×10-6-0.3×10-6. Apply the drug again after 3 days. Generally, two treatments can cure it. Pure freshwater immersion for 2-3 minutes can also be used, and the fish lice can also fall off on their own.