Key Technical Points for Monoculture of Mandarin Fish in Ponds

Mandarin fish, also known as osmanthus fish, has a lower yield per unit area compared with ordinary "domestic fish", but its output value is high. In recent years, it has been highly favored by the vast number of farmers and has become a hotspot in the culture of famous, special and superior fish. The key technical points for monoculture of mandarin fish in ponds are as follows.

1. Pond conditions. Choose a sheltered, sunny site with abundant water, fresh and pollution-free water quality, and convenient drainage and irrigation to build the mandarin fish pond; a pond with loam soil, little silt, or newly excavated is relatively ideal. An area of 600-3000 sq m and a water depth of about 2.0 m are suitable. Equip with an aerator and a bait fish rearing pond, and plant some submerged aquatic plants around the pond, such as Pontederia vaginalis and Hydrilla verticillata, as hiding places for mandarin fish and to absorb excess nutrients in the pond.

2. Stocking size. The suitable size of mandarin fish fingerlings is 5-6 cm. Because mandarin fish have the habit of cannibalism, the stocked fingerlings are required to be uniform in size.

3. Stocking density. The stocking density is closely related to the pond environment, the supply of bait fish and the culture technique, and is generally 800-1200 fish/mu.

4. Bait fish rearing. For monoculture of mandarin fish in ponds, a dedicated pond is needed to rear bait fish, and the area ratio of the mandarin fish pond to the bait fish pond is about 1:4. For bait fish, it is advisable to adopt the culture method of using multiple ponds, rearing at different densities, harvesting in batches, and gradually thinning out, so as to ensure that the bait fish and mandarin fish grow in sync. Generally, crucian carp, common carp, bighead carp, etc., which are easy for mandarin fish to catch and are favored as food, are selected as bait fish; at the same time, the uneaten carp and crucian carp can consume residual bait or decaying matter at the bottom of the pond, preventing water quality deterioration and benefiting mandarin fish culture. To ensure that the size of the bait fish fed is suitable, the feeding and growth of mandarin fish should be checked frequently. The growth and size of bait fish are controlled by adjusting density and feeding amount; the rearing density is 6-8 times that of conventional fish, usually about 1 million fish/mu, and artificial feed can be put in.

5. Feeding. 15-20 days before stocking mandarin fish, rear early-stage bait fish in the pond so that suitable food is available when the fingerlings are put in. After stocking, bait fish should be put into the pond in a timely manner. The suitable length of bait fish swallowed by mandarin fish is 1/4-1/3 of its own length, and the body height should be smaller than the mouth gape of the mandarin fish. Mandarin fish generally prey on active prey by ambush at night, and the amount swallowed is largest at around 8 p.m. Feed once a day, and the feeding amount should be sufficient to meet the food requirement of mandarin fish for 4-5 days; otherwise, the fish are prone to disease and mass death. July-September is the peak growth season for mandarin fish, when the food intake is large, so the feeding amount should be increased timely and appropriately; in winter, the feeding intensity and growth rate of mandarin fish slow down, so the feeding amount can be appropriately reduced. It is best to regularly measure the growth rate of mandarin fish month by month, and if insufficient or unsuitable bait fish are found to affect the growth of mandarin fish, timely adjustments should be made. The ratio of mandarin fish to bait fish in number is 1:5-10. To ensure that the uneaten bait fish can grow normally, an appropriate amount of rapeseed cake should also be fed.

6. Water quality management. Mandarin fish has poor tolerance to low oxygen and a relatively high requirement for dissolved oxygen in the water. According to measurements, under the same conditions, the suffocation point of mandarin fish fry is 3.1 times that of silver carp, 5.1 times that of common carp, and 12.5 times that of crucian carp; once the water is short of oxygen and the fish gasp at the surface, mandarin fish will die first. Therefore, the water used for mandarin fish culture is best fresh, pollution-free, high in dissolved oxygen, and low in pathogenic organisms, such as water from rivers, lakes and reservoirs; if other water sources are used, they must be settled and filtered to prevent harmful organisms from damaging the pond. During the culture process, good water quality can be ensured by measures such as controlling stocking density, adding water, running aerators, and regularly splashing quicklime. It is best to maintain the pond water in a slight flow state. If the dissolved oxygen is above 6 mg/L, the transparency is 30-40 cm, and the pH is neutral or slightly alkaline, etc., this can play a positive role in the growth of mandarin fish and disease prevention.

7. Disease prevention and control. As with other aquatic products, disease prevention and control of mandarin fish must implement the policy of "prevention first, prevention more important than treatment, early treatment of disease, and prevention before disease occurs". Requirements: (1) Before stocking fingerlings, strictly clear the pond by conventional methods; the stocked fingerlings (including bait fish) are required to be healthy and disease-free, and may enter the pond only after being soaked in 2% salt water for 10 minutes; (2) Try to avoid injuring the fish when moving fingerlings; (3) When patrolling the pond, if mandarin fish are found to feed and act abnormally, immediately check and take corresponding measures; (4) During the fish disease epidemic season (May-October), measures such as regularly splashing 30 mg/L quicklime or feeding medicated bait can better prevent the occurrence of fish diseases. For bacterial and parasitic diseases, symptomatic choices include 0.7 mg/L copper sulfate and ferrous sulfate preparation (5:2), 0.2-0.4 mg/L B-type deworming agent, 1 mg/L bleaching powder or 10 mg/L formalin, etc.