Paddlefish Summer Fry and Large-Size Fingerling Rearing Techniques
1. Pond conditions for rearing: sandy-bottom earthen pond, area 2-3 mu, water depth 1.2-1.5 m, silt 15-20 cm, water source and water quality up to standard, rectangular, oriented east-west, length-to-width ratio 5:4 to 3:2, flat pond bottom, convenient water inlet and drainage.
Equip with 1 unit of 1.5-2.2 kW single-phase spray-type aerator, and 1 unit of 2.2 kW single-phase submersible electric pump (4-inch outlet diameter) for adding water to raise the pond water level.
2. Pond clearing and removal of wild fish: quicklime, tea seed cake, croton, bleaching powder and derris root, etc. can be used singly or in combination. For ponds with severe fish diseases, use bleaching powder or quicklime, or tea seed cake plus a small amount of quicklime to clear the pond, so as to improve water quality; this has a certain effect on raising the survival rate of fry and fingerlings.
1) Quicklime pond clearing: drain the pond water to about 10-20 cm, evenly splash lime slurry, with a dosage of about 100-150 jin per 1 mu. For fish ponds where the water source is inconvenient, full-water pond clearing can be used, with a water depth of 1 m and a quicklime dosage of about 250-300 jin per mu.
2) Tea seed cake pond clearing: at a water depth of 1 m, use 80 jin per 1 mu, applied 10-15 days before the fry are stocked into the pond. When water temperature is low, the toxicity disappears slowly; when temperature is high, it disappears quickly. First break the tea seed cake into chunks, put them into a wooden bucket or water vat, add water to soak; at a water temperature of 25°C, soaking for one day and night is enough before use. When applying, increase the amount of water and splash evenly over the whole pond.
3) Bleaching powder pond clearing: at a water depth of 1 m, use 25-30 jin of bleaching powder per 1 mu; dissolve the bleaching powder in water and immediately splash it evenly over the whole pond. The chlorine content of bleaching powder should be about 30%. Fish can be stocked 4-5 days after bleaching powder pond clearing. Bleaching powder pond clearing is related to the fertility of the pond water, and its effect on water fertility is poor.
3. Fry rearing (rearing fry of 3-4 cm each into large-size fingerlings of 15-25 cm each):
1) Fertilizing the pond to build water fertility: the role of fertilization is to cultivate various types of plankton in the water and produce natural palatable food for paddlefish fry after they are stocked into the pond.
2-3 days after disinfection and removal of wild fish, apply 500 jin of fermented manure per mu, or use 2,000 jin of green manure per mu, or use 20 jin of urea + 20 jin of phosphate fertilizer per mu to cultivate plankton; 5-7 days after fertilization, the reproduction of rotifers and plankton reaches its peak.
2) Fry stocking: paddlefish fry of 3-4 cm each should be stocked into the pond on the 5th-7th day after fertilization, when rotifers and cladocerans are at their peak occurrence.
Starting from the 2nd day, feed soybean milk; grind 2-3 jin of soybeans into soybean milk per 1 mu of water surface each day, and feed 2-3 times daily.
4. Stocking density: the general stocking density is 10,000-20,000 paddlefish fry of 3-4 cm each per mu.
5. Fry feeding: at first the fry mainly swallow plankton such as rotifers and small cladocerans in the water body, so fertilization should be used before stocking into the pond; apply organic fertilizer before the fry are stocked to cultivate food organisms, then use the soybean milk feeding method, splashing soybean milk into the pond, most of which serves to fertilize the water and reproduce rotifers.
Within 5-7 days after the fry are stocked into the pond, feeding soybean milk is the main method; when grinding soybean milk, the soybeans must be soaked until swollen, and after grinding the soybean residue must be removed. When feeding, splash over the whole pond, and make the splashed slurry look like raindrops and be evenly distributed.
After 5-7 days, feed eel feed or young soft-shelled turtle feed or yellow catfish floating compound feed ground into powder for the fry to eat. If the number of rotifers and red worms in the pond is not large, appropriately supplement fertilizer, and add clean water to increase dissolved oxygen and promote the growth of rotifers and red worms. Feed twice daily, at 8 a.m. and 7 p.m.
6. Fry food organism cultivation: 3 days after pond clearing, apply 500-600 jin of decomposed chicken manure or 400-500 jin of decomposed cow manure and 200-300 jin of green manure per 1 mu, then fill with water to 40-50 cm (to cultivate red worms and rotifers); when filling with water, strictly filter with 80-mesh silk gauze cloth to prevent wild trash fish from entering.
7. Fry stocking: when paddlefish summer fry are transported from the fry hatching base to the rearing pond, the stocking operation requires acclimation——place the packaging bag directly into the water; after 15-20 minutes, use a thermometer to check the water temperature inside and outside the bag; when the temperature difference is within 1-2°C, slowly pour the fry into the pond at the upwind side with the bag opening level with the pond water surface.
8. Water level management of the rearing pond: 5-7 days after stocking, appropriately raise the pond water level every 2-3 days, adding 8-10 cm each time, gradually raising the pond water to 1-1.5 m. When filling with water, use a fine net at the water inlet to filter out wild trash fish and harmful insects, and at the same time avoid the water flow directly hitting the pond bottom and stirring the pond water muddy.
9. Water quality regulation: at stocking, the pond water transparency should be below 30 cm, after which appropriately apply supplementary fertilizer to control the fertility of the pond water. In summer, the pond water transparency should be controlled at about 25-30 cm, and in autumn maintained at about 35 cm.
10. Pond patrol management: after the fry are stocked in the pond, patrol the pond three times a day, carrying out the “three checks” and “three diligent tasks.”
In the morning, check the floating-head condition of the fry and diligently remove frog eggs; in the afternoon, check the activity of the fry and diligently remove weeds on the pond embankment; in the evening, check the water quality, diligently keep records, and arrange the next day's feeding, fertilization and water addition work. At all times pay attention to checking for the occurrence of diseases and carry out timely prevention and treatment.
11. Daily management: the main work is pond patrol, once in the morning and once in the afternoon, observing the activity of the fish in the pond and changes in water color and water quality, taking timely measures and determining the feeding amount when problems are found, timely removing weeds at the pond edge, and also paying attention to cultivating and regulating water quality; through measures such as reasonable water filling and fertilization, make the pond water have both abundant palatable natural food and sufficient dissolved oxygen.
Observe diligently, prevent floating head, prevent fish diseases: paddlefish fry cannot tolerate low oxygen, and the phenomenon of fry floating head due to oxygen deficiency absolutely must not occur; during the fingerling rearing stage, patrol the pond morning and evening. To prevent oxygen deficiency in the pond water caused by weather changes, frequently add new water and turn on the aerator to regulate water quality.
12. Domestication of large-size fry:
a. Guiding fish with flowing water: before feeding, use a water pump to flush water, 1-1.5 hours each time. When flushing water, keep the outlet as level as possible with the pond water surface; the outflow rate depends on the pond area. Fry have the habit of swimming against the current; the main function of flushing water is to gather the fry together to facilitate domestication. The pump outlet should be as close to the pond edge as possible to achieve the best effect of gathering the fish school.
b. Installation of feeding site and feeder: set up a circular or square feeding site where the fish school gathers at the pump outlet. Use four bamboo poles with a diameter of 3-4 cm (each 3-4 m long), connected into a square enclosure; place the enclosure into the pond, with its position matching the feeding area of the feeder, then fix it with anchors or stakes, and install the feeder.
c. Feeding: after 1 hour of water flushing, turn off the water pump and begin manually or mechanically scattering an appropriate amount of artificial feed into the feeding site; the particle size of the feed fed must not be too large, usually below 1 mm.
d. Feeding time: on sunny days, feed 5-6 times daily, about 30 minutes each time. The feeding amount depends on the size of the fish school, and the feed must be cast within the feeding site. Generally after 2-3 days of domestication, fry can be seen feeding in the middle water layer; after 5-6 days, fry can appear snatching food at the water surface, at which point domestication is complete.
e. After domestication is completed, enter the normal feeding stage: feed 2-3 times daily, after 8:00 a.m. and before 5:00 p.m. Feed according to the feeding condition of the fry and the weather; the daily feeding amount is 5-6% of the total fish weight.
13. Daily management of the fry rearing pond: patrol the pond once in the morning and once in the evening, remove debris from the pond. Observe water color and fish activity, pay attention to weather, water temperature, water color, feeding conditions, etc., and keep detailed records.
14. Water quality regulation of the fry rearing pond: before the fry are stocked, control the water depth at about 50-60 cm, and the water quality should be fertile but fresh; after stocking, according to water color and weather, flush water once every 2-3 days, about 8-10 cm each time, and later control the water depth at 1-1.5 m.
On sunny days from 12:00 to 14:00, start the aerator to aerate for 1-1.5 hours to stir the pond water and increase dissolved oxygen. Every 15-20 days, splash 20 kg of quicklime per mu once to maintain pH between 7 and 8. During the entire rearing process, add water 5-7 times, 8-10 cm each time.
15. Catching of paddlefish fry: because paddlefish belong to upper-layer fish and are relatively gentle in temperament, the catch rate by seining is relatively high.
16. Precautions during the summer fry rearing process:
Paddlefish fry like to live in fresh, slightly alkaline water quality with sufficient dissolved oxygen; therefore, during the rearing process, quicklime should often be used to regulate water quality, new water should be added, and the aerator should often be turned on to increase oxygen, so that the pH of the water body is between 7 and 8 and the dissolved oxygen content is above 6 mg/L.