What points should be noted in sturgeon fry rearing?
With the vigorous rise of sturgeon aquaculture, the price of commercial sturgeon keeps falling, and the profit margin is getting smaller and smaller. Improving the survival rate of sturgeon fry and fingerlings is one of the main means of increasing profits in sturgeon aquaculture. Farming sturgeon in the south generally requires southward relocation and acclimation, which places special demands on the ecological conditions of the farming site, the farming facilities and basic operational management. Below, based on the lessons and experience of sturgeon farming in recent years, the author discusses some technical points in the stage of sturgeon fry and fingerling rearing.
Water quality requirements
The basic water quality requirements for sturgeon fry and fingerling rearing are: pH 6.5-8.0, dissolved oxygen greater than 6.0 mg/L, total iron content less than 0.8 mg/L, non-ionic ammonia less than 0.02 mg/L, and nitrite nitrogen less than 0.05 mg/L. Each farm should, according to the condition of its own water source, compare it with the above basic water quality requirements for sturgeon and treat the water appropriately. If the water source is well water, the main thing to monitor is whether the total iron content exceeds the standard; if the water source is river water, especially river water with pollution sources, the main things to monitor are whether suspended solids and ammonia nitrogen content exceed the standard; if the water source is stream water, the main thing to monitor is whether the pH value is too low; if any exceed the standard, well water and river water can be well treated by aeration plus quartz sand filtration; acidic stream water can be adjusted in pH with quicklime.
Production facilities
Newly built sturgeon fry and fingerling rearing ponds are generally required to be built as flowing-water fish ponds, with a pond area of 0.5-2 sq m, a pond depth of 0.8-1.0 m, a circular pond shape, a pot-shaped pond bottom, and a drainage outlet in the middle for sewage discharge; the water inlet is set at the upper part of the pond in the shape of a flute pipe. The bottom of the rearing pond at the yolk-sac fry stage should be smooth; if it is a cement pond, the bottom should be laid with ceramic tiles. If conditions permit, aeration and oxygen-increasing facilities can be set up in the pond.
Yolk-sac fry quality
The quality of yolk-sac fry is one of the factors affecting the survival rate of sturgeon fry and fingerlings. Therefore, when purchasing sturgeon yolk-sac fry, farmers should strictly check the quality of the fry. Good-quality yolk-sac fry should swim actively up and down in the water two days after hatching, with fewer fry lying still in clusters at the bottom of the water for long periods; such sturgeon yolk-sac fry have a high survival rate in transport and a stronger ability to adapt to the environment during the rearing process.
Daily management
1. Stocking density: for sturgeon yolk-sac fry from the still-lying stage to the pre-first-feeding stage, the stocking density in flowing-water fish ponds is generally 3000-5000 fry/sq m, and after first feeding it can be adjusted to 2000 fry/sq m; as the fry and fingerling size continues to grow, the stocking density should be reduced in a timely manner.
2. Sewage discharge: discharge sewage at least once a day; during the larval stage, sewage can be discharged by siphon method with a thin rubber tube; during the juvenile stage, sewage can be discharged automatically by flowing water.
3. Water change: although the rearing pond is designed as a flowing-water pond, the water flow cannot be opened very large during the fry and fingerling rearing stage, so the water still needs to be changed once a day, with the water change amount being two-thirds of the pond water.
4. Feeding: the first-feeding bait for various sturgeons is generally aquatic earthworms, and using brine shrimp as the first-feeding bait also gives good results. Before feeding, aquatic earthworms should be rinsed clean with water, then disinfected with furazolidone (3 ppm) or potassium permanganate (10 ppm), chopped and fed. The feeding frequency is 6-8 times/day, and the feeding amount is 40%-50% of the fish body weight.
5. Water temperature: the water temperature for sturgeon fry and fingerling rearing is best controlled at 18-25°C.
Prevention and treatment of common diseases
1. Gas bubble disease: the main symptom of this disease is that the abdominal cavity of the fry swells with gas and expands, and they float on the water surface making irregular movements; it will not cause large-scale death. The treatment method is to splash salt into the water so that the pond water reaches a concentration of 0.5%.
2. Enteritis disease: the main symptoms are that the fish body turns black and swims alone away from the group; dissection shows congestion of the intestine and anus, with no food in the intestine; if not treated in time, it can cause large-scale death. For treatment, furazolidone (10-20 mg per kg of fish per day) can be mixed into the food and fed for 3-5 consecutive days.
3. Red mouth disease: the main symptom is red swelling around the fish's mouth, making it difficult to eat, and it very easily causes death. Enrofloxacin can be splashed over the whole pond so that the pond water reaches a concentration of 1 ppm, with good results.
4. Tail rot disease: the main symptom is that the tail fin of the diseased fish becomes rotten, sometimes accompanied by ulceration of the pectoral fins; the infection rate is high and death occurs easily. For treatment, furazolidone can be splashed over the whole pond so that the pond water reaches a concentration of 3 ppm.