Techniques for Rearing Yellow Catfish Summer Fry and Food Habit Domestication
1. Pond conditions: area 3-5 mu, water depth 1.2-1.8m, mud 15-20cm, water source and water quality up to standard. The pond is rectangular, running east-west, with a length-to-width ratio of 5:4 to 3:2, and convenient water inlet and drainage.
2. Pond clearing and disinfection: Use quicklime or bleaching powder to clear and disinfect the pond, using the dry method, leaving 10-15cm of water in the pond. 7-10 days before stocking, use 150-200 jin of quicklime or 25-30 jin of bleaching powder per 1 mu to clear and disinfect the pond.
3. Fertilizing to cultivate natural bait: From the time yellow catfish fry are put into the pond until they reach a total length of 3cm, their food consists of rotifers, nauplii, cladocerans, copepods and benthic animals.
Before the fry are put into the pond, sufficient base fertilizer must be applied to cultivate suitable natural bait, so that as soon as the fry are stocked they can promptly and fully prey on suitable natural bait, which helps increase the survival rate of the fry.
3-5 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 mu, then fill with water to 40-50cm to cultivate red worms and rotifers. When filling with water, filter it through 80-mesh silk gauze to prevent wild miscellaneous fish from entering. One day before the fry are stocked, pull an empty net once to remove frog eggs and tadpoles.
3 days before the fry are put into the pond, soybean milk must also be splashed over the whole pond, using 2-3 jin of dry soybeans per mu per day, soaked and then ground into soybean milk and splashed over the whole pond.
4. Stocking the fry: Generally, purchased fry are smaller in size. After buying them back, they must first be intensively reared for 2-3 days in a small cement pond or net cage, and once they reach more than 1.2cm (preferably around 1.5cm), they are then put into earthen ponds for fry rearing, which helps increase the survival rate.
5. Method of stocking the fry: Stocking yellow catfish fry should be done on a clear morning around 9 o'clock, because the air temperature is relatively high during the fry emergence stage, while at 9 o'clock in the morning the temperature is still acceptable and the oxygen conditions in the water are gradually improving. Stocking at this time helps the fry adapt to the water temperature and other environmental conditions, and their vitality is also stronger.
When stocking the fry, they must be spread out and released, and must not be allowed to pile up, otherwise it will cause large-scale death and thus affect the survival rate of the entire fry rearing.
6. Fry stocking density: The stocking density for yellow catfish fry rearing is lower than that of other conventional fish. Usually, stocking about 80,000-100,000 fry of around 1.5cm per mu is sufficient; excessive density instead has a negative impact on the fry rearing effect, and management difficulty will also increase accordingly.
7. Precautions for fry stocking: In the operation of stocking newly hatched fry, temperature acclimation must be carried out——first place the packaging bag directly into the water, and after 15-20 minutes, use a thermometer to check the water temperature inside and outside the bag. When the temperature difference is within 0.5-1 degree C, slowly pour the fry into the pond from the bag mouth at the upwind end of the pond, level with the pond surface.
8. Fry bait feeding: On the 2nd-3rd day after stocking, check the number of rotifers and red worms in the water. Use 3-5 jin of soybean milk per mu per day, splashed to cultivate rotifers and red worms, splashing twice a day in the morning and evening. During the fry rearing process, if rotifers and red worms are not replenished in time, the fry cannot get bait and will quickly become emaciated and convulse to death, directly affecting the fry rearing survival rate.
9. Fry food habit domestication: 3-5 days after stocking, appropriately increase the amount of eel feed or young soft-shelled turtle feed ground into powder (crude protein content 42-46%) 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.
Domestication steps: Domestication can begin 3-5 days after the fry are put into the pond. First, select about 10 feeding points per mu of pond for fixed-point feeding, using minced fish or soft-shelled turtle feed or eel feed made into balls, and put them at feeding points about 40cm below the water surface after 4 o'clock every afternoon.
After 4 days, reduce one feeding point, and thereafter reduce one feeding point every 3-4 days, until finally two feeding points remain. Build the feeding platform, and change from feeding once a day to feeding twice a day.
The feeding platform must be about 40cm below the water surface, which is favorable for yellow catfish feeding. The fry are finally domesticated to concentrate on eating artificial compound feed, which makes it convenient to check the fish's feeding situation and to prevent and treat diseases.
10. Water level management of the fry rearing pond: 5-7 days after stocking, appropriately raise the pond water level every 2-3 days, adding 8-10cm each time, gradually raising the pond water to 1-1.2m.
11. Exercising and pond division: After 20-25 days of rearing, when the yellow catfish have grown to about 2.5-3cm, sorting and separate rearing should be carried out. Before the summer fry leave the pond, they must be exercised by netting 2-3 times. This enables the fry, during the crowding process, to increase their body's ability to adapt to hypoxia, makes the fish body "seasoned" and sturdy, able to withstand out-of-pond division and rearing, and avoids producing large amounts of mucus and feces during transport that pollute the water quality, thus increasing the transport survival rate. Netting exercise can also remove harmful organisms and estimate the number of summer fry.
1) First netting: Gather the summer fry in the net, check their physique, then immediately release them back into the pond. The operation must be careful.
2) Second netting: After an interval of 1 day, carry out the second netting exercise. After the fish are gathered, let them swim against the water automatically into the net cage. At this time, a fry sieve can be used to screen out female and male fry, and after 2-3 hours release them back into the pond.
3) Third netting: After the second netting, wait another 1 day, then carry out the third netting. Put the fry into a net cage in a pond with clearer water and "hang-rear" them for 1 night. At this time, a fry sieve can also be used to screen out female and male fry, and the next morning they can be loaded for long-distance transport.
For exercising the fry, be sure to choose clear, fine weather, and carry out the work in the morning when the fish are not surfacing for air. The operation of netting and driving the fish must be slow, so as not to injure the fry. When closing the net, the fish must not be allowed to press against the net. After the fish enter the cage, the cage should be washed once immediately, to wash away the sticky excrement and dirt on the mesh, so that the water inside the cage flows freely with the outside, preventing fry death caused by hypoxia inside the cage.
12. Methods for domesticating the food habits of yellow catfish fry:
a. Reduce the total amount of animal bait in the water body: During the early fry stage of yellow catfish, methods such as splashing soybean milk and applying biological fertilizer are usually used to cultivate animal bait. Before food habit domestication of yellow catfish, these operations must be stopped to reduce the total amount of animal bait in the pond. For ponds relatively rich in animal bait, necessary measures must be taken to kill the bait animals.
Specific method: At the downwind place where zooplankton gather, covering 1/5-1/3 of the pond area, splash crystalline trichlorfon so that its concentration reaches 0.01-0.02ppm.
b. Seize the timing and choose the appropriate size: Begin artificial domestication when the yellow catfish reared in the pond reach a size of about 3cm. For domesticating yellow catfish, artificial bait of a certain particle size must also be prepared according to the size of the yellow catfish.
c. Attracting fish with flowing water: For 1 week before feeding, use a water pump to flush water twice a day, in the morning and evening, for 2-3 hours each time. When flushing water, keep the outlet as level as possible with the pond water surface; the water output is determined by the pond area. Yellow catfish have the habit of swimming against the current; the main effect of flushing water is to gather the yellow catfish together, which facilitates domestication. During the fry stage, yellow catfish generally gather at the pond edge, so the pump outlet should be as close to the pond edge as possible to achieve the best fish-gathering effect.
d. Installation of feeding ground and feeder: Set up a round or square feeding ground where the fish gather at the pump outlet. Use four bamboo poles with a diameter of 3-4cm (each 3-4m long) connected into a square enclosure, place the enclosure into the pond at a position matching the feeding area of the feeder, and then fix it with anchors or stakes. The feeding ground can also be made from PVC pipe or 40-mesh netting cut into narrow strips.
e. Starvation feeding: 2-3 hours after flushing water begins, start manually scattering an appropriate amount of artificial feed into the feeding ground, and close the water pump before feeding. The feed particle size must not be too large, usually below 1mm. If suitable particle size is unavailable, large-particle feed can be soaked in an appropriate amount of water and kneaded into pieces.
f. Feeding time: Base it on after the sun sets on clear days and before the sun rises in the morning, feeding twice a day, about 30 minutes each time. The feeding amount depends on the size of the fish school, and the feed must be thrown within the feeding ground. Generally, after 3-5 days of domestication, yellow catfish can be seen feeding in the mid-water layer; after 6-8 days, yellow catfish can appear snatching food at the water surface, at which point a feeder can be used instead.
g. After domestication is completed, enter the normal feeding stage: Feed twice a day, before 8:00 in the morning and after 5:00 in the afternoon. Feed according to the fry's feeding situation and the weather, with a daily feeding amount of 6-8% of the total fish weight.
13. Daily management of the yellow catfish fry rearing pond: Patrol the pond once in the morning and once in the evening, scoop out dirt, frog eggs, etc. from the pond. Observe the water color and the fish's activities, and arrange the next day's feeding amount, water filling and disease prevention work, etc. Pay attention to weather, water temperature, water color, feeding conditions, etc., and keep detailed records.
14. Water quality regulation of the yellow catfish fry rearing pond: Before the fry are stocked, control the water depth at about 50-60cm, 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 8-10cm each time, and later control the water depth at 1-1.2m.
On clear days from 12:00 to 14:00, start the aerator for two hours to aerate, stirring the pond water to increase dissolved oxygen. Every half month, splash 15ppm quicklime once to keep the pH between 7 and 8. Throughout the entire rearing process, fill water 5-7 times, 8-10cm each time. Every half month, administer medicated bait once, for three days each time, using 0.1% tetracycline or oxytetracycline mixed with feed to prevent fish diseases.
15. Catching yellow catfish fry: Because yellow catfish are benthic fish and relatively gentle in temperament, the catch rate by netting is relatively high. Using a net with suitable mesh size and pulling it back and forth 2-3 times in the rearing pond, more than 80% of the yellow catfish fry in the pond can be caught.
16. Precautions during the yellow catfish summer fry rearing process:
a. Yellow catfish newly hatched fry are only 3-5mm in body length, with a relatively large yolk sac and weak activity; they like to gather at the bottom of the water body and rely on absorbing the yolk for nutrition. As the individuals gradually grow, the yolk sac gradually shrinks and their free-swimming ability gradually improves, but their adaptability to the ecological environment is poor, and they can only take food under dark, low-light conditions. They should first be reared in ponds without mud slurry, without pollution, with fresh water quality and relatively high dissolved oxygen.
b. Before the yellow catfish fry reach 2cm in body length, they mainly feed on rotifers, red worms, cladocerans, chironomid larvae, etc., similar to the four major Chinese carps, and afterward gradually change to omnivorous feeding mainly on animal food. However, if the same fry rearing method as for the four major Chinese carps is adopted, the survival rate of the fry will be affected. Therefore, cultivating biological bait such as rotifers before stocking the newly hatched fry is the key to increasing the fry rearing survival rate.
c. Yellow catfish like to live in fresh water quality that is slightly alkaline and fully oxygenated. Therefore, during the rearing process, quicklime should often be used to regulate water quality, add new water, and often start the aerator to increase oxygen, so that the pH of the water body is between 7 and 8 and the dissolved oxygen content is above 6mg/L.
d. During the rearing process, administering medicated bait once every half month can effectively prevent the occurrence of diseases.
e. When rearing yellow catfish summer fry in ponds, ensure that the same batch of fry is stocked into the pond, and stock the full quantity at one time.
f. During the food habit domestication period, yellow catfish fry must never be netted for exercise, so as to avoid domestication failure.
17. Special precautions: Yellow catfish is a scaleless fish, and its tolerance to commonly used aquaculture drugs is less than that of the four major Chinese carps. The 24-hour semi-lethal concentrations of several commonly used drugs are: copper sulfate 0.69 mg/L, 90% crystalline trichlorfon 2.8 mg/L, table salt 25 g/L, formalin 68 mg/L.
When administering drugs to yellow catfish, the dosage must be strictly controlled to avoid drug poisoning. Yellow catfish are relatively sensitive to malachite green, copper sulfate, mercurous nitrate, potassium permanganate and trichlorfon, and these must be handled with special caution.
18. Transport of fry and fingerlings: In the process of transporting fry and fingerlings, no matter what method is used, the operation must be meticulous, and attention should be paid to the following aspects:
1) The fry should be robust and swim actively. For oxygen-filled nylon bag transport, the loading amount is about 80% of the transport box.
2) The water quality should be fresh and non-toxic, with high dissolved oxygen. Water from rivers, lakes, reservoirs and ponds can all be used; choose colorless, transparent water with low mud content. Tap water must be dechlorinated and left to stand for 24 hours before use. In summer, use cool water.
3) Before the fingerlings are shipped, the fish body must be exercised by netting to expel feces. Only when the body is firm and mucus secretion is reduced can the survival rate be increased.
4) Pay attention to temperature balance; the temperature difference must not exceed ±2 degrees C. After arriving at the destination, first put them into the cage to revive the fish. One hour later, feed the fry cooked egg yolk. For 100,000 fry, feed one egg yolk. After seeing the fry's intestines filled (swallowing egg yolk into the intestines), wait another hour before releasing the fish into the pond. For fry in nylon bags and transport boxes, before putting them into the cage, first place them in the water so that the internal and external water temperatures are the same. Then open the nylon bag or transport box, pour in pond water, put the bag into the cage, and let the fry (fingerlings) swim out on their own.