Detailed Explanation of Paddlefish Farming Methods and Technical Key Points

1. Fry rearing 

 

Generally, the water tank rearing method is adopted. After hatching, the fry are reared in tanks for 30 to 40 days until they reach 3 to 5 cm and are transferred to ponds. This process is key to fry survival. 

 

(1) Tank conditions: an area of about 10 sq m, either rectangular or circular, with no sharp corners, convenient water inlet and outlet, and escape-prevention facilities. The water quality must be excellent, free of pollution and toxic substances, and filtered before use. Water exchange is carried out twice per hour (water is stopped for half an hour during feeding), the water temperature is between 16 and 28°C, and the dissolved oxygen is above 5 mg/L. 

 

(2) Stocking density of paddlefish fry: initially 200 fish/sq m, and when they grow to 5 cm the density is reduced to 100 fish/sq m. 

 

(3) First feeding and feeding: the first feed for paddlefish is zooplankton, and a combination of egg yolk and zooplankton can also be used. The best first feed for paddlefish is the copepod Cyclops. If Cyclops is fed, the timing of introduction must be well controlled, so as to prevent Cyclops from piercing the yolk sac of the fry and causing mass mortality. The daily feeding frequency should be 4 to 8 times, and feeding is also required at night in indoor rearing rooms; the amount should be such that a slight surplus remains. The feed introduced in the early stage needs to be passed through a 60-mesh sieve to screen out large individuals and harmful aquatic insects. In the later stage, after acclimation, they can consume artificial compound feed, with intake of about 30% of body weight. Paddlefish have extremely poor eyesight and do not actively search for food, so losses during feeding tend to be somewhat greater. 

 

(4) Daily management and precautions: daily management requires draining sewage, scrubbing the mesh screens, and keeping detailed records. When the fry grow to 3 to 5 cm, several abnormal situations occur, such as gathering in the corners of the tank, biting and devouring one another, and uneven individual sizes. The causes of these situations are uneven nutrition and excessive density. In addition, due to insufficient nutrition, the fry will also swallow air bubbles on the water surface, causing the digestive tract to swell and bleed until death. Of fry deaths, 80% are caused by biting and devouring one another, and about 20% by congestion of the digestive tract. Therefore, fry after 3 to 5 cm should be transferred to ponds with balanced and sufficient feed and a large water body 

 

2. Pond rearing of fingerlings 

 

Fry of 3 to 5 cm are reared within the same year into large-size fingerlings of 20 to 30 cm in body length and 200 g in body weight, which takes 3 to 4 months. 

 

(1) Pond requirements: ponds with a water surface of 3 to 5 mu, a water depth of 1.5 to 2 m, and convenient water inlet and outlet are better, and each pond should be equipped with a 1.5 kW aerator. Before stocking, the pond must be cleared with water present, using 150 to 200 kg of quicklime per mu to kill miscellaneous fish, aquatic plants and so on. The pond water temperature can be 2 to 37°C, with 25 to 32°C being optimal. 

 

(2) Manuring and stocking: one week before stocking, fertilization must be carried out to cultivate good water quality; the fertilizers are generally night soil (400 to 500 kg/mu) and chicken manure, cow manure, etc. After 3 days, soybean milk is spread into the pond at 5 kg/mu. Before stocking, the pond must be swept once more with a fry net to remove tadpoles and debris, and the temperature difference between the pond water and the water in the container holding the fish must not exceed ±3°C; the operation should preferably be carried out in the evening. 

 

(3) Reasonable sparse stocking: the main farming method is monoculture, and a small number of bottom-dwelling fish and herbivorous fish can be stocked together, but never silver carp, bighead carp or fierce predatory fish. The stocking density is preferably 100 fish per mu. During the farming process, in addition to fertilizing to cultivate the water body, soybean milk (2 kg/mu), oilseed cake meal, floating wheat flour, bran or special pellet feed must also be fed, and the water quality must always be maintained as fertile, lively, tender and refreshing. 

 

(4) Strengthen management: insist on patrolling the pond every day and carefully keep farming records. 

 

(5) Fish diseases and treatment: generally, fingerlings over 10 to 15 cm rarely die, but there have been several reports of parasitic and bacterial diseases. Because paddlefish are very sensitive to drugs, especially to heavy metal salt drugs, caution is required when using medication. Occasional fish diseases are mainly nematodes and trematodes, which can be treated with a medicated bath of 2×10-6 potassium permanganate or less than 75×10-6 formalin. During the juvenile stage, copper sulfate and chlorine-containing drugs are prohibited, and the soaking concentration for antibiotics is about 4×10-6. After being reared into large-size fingerlings of 30 to 40 cm, they can be directly released into reservoirs, or they can continue to be farmed in ponds. 

 

3. Release 

 

(1) The size should be 30 to 40 cm or larger, to ensure their survival ability and defend against other fierce predatory fish.