Breeding Techniques for Bighead Carp Summer Fry and Large-Size Yearling Fingerlings
Pond Selection
The bighead carp fry rearing pond has an area of 3-5 mu, rectangular, oriented east-west, with a length-to-width ratio of 5:4 to 3:2, an average water depth of 1.2-1.5 m, a pond slope ratio of 1:1 to 1:1.5, a flat bottom, loam soil, a silt thickness of 15-20 cm, and convenient water intake and drainage.
The bighead carp fingerling rearing pond has an area of 10-15 mu, rectangular, oriented east-west, with a length-to-width ratio of 5:4 to 3:2, an average water depth of about 1.8-2.5 m, a pond slope ratio of 1:1 to 1:1.5, a flat bottom, loam soil, a silt thickness of 15-20 cm, and convenient water intake and drainage.
Pond Clearing and Removal of Wild Fish
Quicklime, tea seed cake, croton, bleaching powder and derris root can be used alone or in combination. For ponds with severe fish diseases, bleaching powder or quicklime, or tea seed cake plus a small amount of quicklime, is used for pond clearing to improve water quality, which has a certain effect on increasing 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 with inconvenient water sources, full-water pond clearing can be adopted, with a water depth of 1 m and a quicklime dosage of about 250-300 jin per mu.
2. Tea seed cake pond clearing: With a water depth of 1 m, the dosage is 80 jin per 1 mu, applied 10-15 days before the fry are stocked into the pond. At low water temperatures, the toxicity disappears slowly; at high temperatures, it disappears quickly. First break the tea seed cake into pieces, put them into a wooden bucket or water vat, add water to soak, and at a water temperature of 25°C, soak for one full day and night before use. When applying, add a large amount of water and evenly splash over the entire pond.
3. Bleaching powder pond clearing: When the water depth is 1 m, the bleaching powder dosage is 25-30 jin per 1 mu; dissolve the bleaching powder in water and immediately splash evenly over the entire pond. The chlorine content of bleaching powder should be about 30%. Fish can be stocked 4-5 days after bleaching powder pond clearing. The effect of bleaching powder pond clearing is related to the fertility of the pond water; in fertile water, the effect is poor.
Fry Rearing
1. Pond fertilization to cultivate water quality: The role of fertilization is to cultivate various types of plankton in the water, producing the first food for the 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 apply 2,000 jin of green manure per mu, or apply 20 jin of urea + 20 jin of phosphate fertilizer per mu to cultivate plankton. 5-7 days after fertilization, rotifers and plankton reach their peak reproduction.
Fertilization effect: After pond fertilization, the initially appearing dominant plankton populations are related to the nature of the fertilizer. With organic fertilizer applied, phytoplankton such as chrysophytes and cryptomonads, and zooplankton such as trichodinids and peritrichs, first appear in large numbers. With inorganic fertilizer applied, diatoms, Scenedesmus and halteriids become the main populations.
When the fertilization amount is large, some species of green algae and blue-green algae will develop in large numbers; when the fertilization amount is small, many species of diatoms, such as spindle-shaped diatoms and disc-shaped diatoms, will become the dominant species.
4-5 days after fertilization, zooplankton can reach their peak. The zooplankton that first appear in large numbers are protozoans and rotifers, followed by cladocerans, and then copepods.
After pond fertilization, if the pond water appears light greenish-brown, with large numbers of algae, protozoans and rotifers reproducing in the pond, and cladocerans just beginning to appear, it is most suitable for the growth of bighead carp fry.
2. Timing of fry stocking: The bighead carp water fry should be stocked into the pond on the 5th-7th day after fertilization, when the rotifers and cladocerans are at their peak occurrence.
When releasing the fry, feed 1 cooked egg yolk per 100,000 fry so they are stocked with full stomachs. Starting from the 2nd day, feed soybean milk, grinding 2-3 jin of soybeans into soybean milk per 1 mu of water surface per day, feeding 2-3 times.
3. Fry stocking: The fertility should be moderate when stocking into the pond. Before stocking, the fry are first placed in a fry box and fed cooked egg yolk, with a feeding amount of 1 cooked egg yolk per 100,000 fry. Feeding cooked egg yolk should be carried out according to the following steps:
1) Boil the egg yolk a little longer, wrap the egg yolk in 60-mesh nylon sieve cloth, and wash and filter it by beating and shaking in a basin of water; do not squeeze it with your hands, so that fine egg yolk particles pass through the mesh into the water;
2) Use your fingers to evenly drizzle the egg yolk water into the fry box; after half an hour, egg yolk particles can be seen in the intestines of the bream fry (commonly known as flower intestine);
3) After keeping them in the fry box for 3-4 hours, release the fry into the pond.
4. Stocking density: The general stocking density is 150,000-200,000 fry per mu. If the fry are seined and divided into ponds when they grow to a total length of 2-2.5 cm, the stocking density can be increased to 250,000-300,000 fry per mu.
5. Fry feeding: When the fish are too small at first, they mainly swallow rotifers, small cladocerans and other plankton in the water body, so fertile water stocking should be adopted, applying organic fertilizer before the fry are stocked to cultivate food organisms, and then adopting the soybean milk feeding method; the soybean milk is splashed into the pond, part of it is eaten by the fry, and most of it plays a role in fertilizing the water. The general feeding amount is 4-6 jin of soybean milk ground from soybeans per mu per day, increased to 8-10 jin after one week, and the amount is controlled according to water color, with a water-to-soybean ratio of 30:1.
Within 5-7 days after the fry are stocked, feeding is mainly soybean milk. When grinding soybean milk, the soybeans should be soaked until swollen, and the okara should be removed after grinding. When feeding, splash the milk along the pond edge in two circles, and make the splashed milk resemble raindrops, evenly distributed. After 5-7 days, feed powdered fine feed such as refined flour, rice bran and wheat bran. Feed twice a day, at 9 a.m. and 4 p.m.
After 25-30 days of rearing, the fry can reach a size of over 3.3 cm, and the daily feeding amount is 15-20% of the fish body weight.
6. Staged water addition: Add fresh water to the pond in stages to raise the pond water level, so as to increase the dissolved oxygen content in the water, improve water quality, expand the activity space for the fry, and accelerate fish growth. This promotes plankton reproduction and increases live food organisms.
When the fry enter the pond, the pond water depth is about 0.6-0.7 m; at 7-15 days of rearing, the pond water depth is increased to 1 m; at 20-30 days of rearing, the pond water depth is increased to 1.2 m; at 40-45 days of rearing, the pond water depth is increased to 1.5 m.
When adding water, use a fine mesh net at the water inlet to filter out wild fish and harmful insects, and at the same time avoid the water flow directly hitting the pond bottom and stirring the pond water muddy.
7. Water quality regulation: When releasing the fry, the pond water transparency is below 30 cm; afterward, apply additional fertilizer appropriately to control the fertility of the pond water. In summer, the pond water transparency is controlled at about 25-30 cm; in autumn, it is maintained at about 35 cm.
8. Pond patrol management: After the fry are stocked, patrol the pond three times a day, carrying out the "three inspections" and "three frequent tasks."
In the morning, check the floating-head condition of the fry and frequently remove frog eggs; in the afternoon, check the activity of the fry and frequently remove weeds on the pond embankment; in the evening, check the water quality, frequently keep records, and arrange the next day's work such as feeding, fertilizing and adding water. Always pay attention to checking for the occurrence of diseases and carry out timely prevention and control.
9. Daily management: The main work is pond patrol, once in the morning and once in the afternoon, observing the activity of the pond fish and changes in water color and water quality, taking timely measures and determining the feeding amount when problems are found, and timely removing weeds around the pond. In addition, attention should be paid to cultivating and regulating water quality; through measures such as reasonable water addition and fertilization, the pond water should have both abundant palatable natural food and sufficient dissolved oxygen.
Observe frequently, prevent floating head, prevent fish diseases: During the fingerling rearing stage, patrol the pond in the morning and evening. To prevent oxygen deficiency in the pond water caused by weather changes, frequently add fresh water to regulate water quality.
10. Feeding technique and feeding amount: After the body length reaches 2-2.5 cm, feed powdered compound feed, with a daily feeding rate of 10-15%.
11. Disease prevention and control: The main diseases during the bighead carp fry and fingerling rearing stage are parasitic diseases, such as trichodinosis, fish lice and anchor worms.
Prevention and control method: Regularly splash crystal trichlorfon and copper sulfate over the entire pond to make the pond water concentration reach 0.3 g per cubic meter, and splash once more the next day to achieve prevention and control.
12. Training and pond division: After 20-25 days of rearing, when the bighead carp fry grow to about 3 cm, they should be divided for rearing. Before the summer fry leave the pond, they must undergo 2-3 seining trainings. This enables the fingerlings, during the process of being crowded together, to increase their adaptability to oxygen deficiency. It makes the fish body "seasoned" and sturdy, able to withstand being taken out of the pond and divided for rearing, and avoids producing large amounts of mucus and feces during transport that would pollute the water quality, thereby increasing the transport survival rate.
1) The 1st seining: Gather the summer fry in the net, check their physical condition, and then immediately release them back into the pond. Because the fish body is tender, the operation must be careful.
2) The 2nd seining: After an interval of 1 day, carry out the 2nd seining training. After gathering the fish together, let them swim against the water automatically into the net box. After two hours, release them back into the pond. If they are to be kept for self-rearing, then after 2 seining sessions and crowding in the box, they can be divided for rearing.
3) The 3rd seining: After the 2nd seining, wait another 1 day, then carry out the 3rd seining, placing the fingerlings into a net box in a pond with clearer water for "hanging rearing" for 1 night; the next morning they can be loaded for long-distance transport.
For training the fry, be sure to choose fine sunny weather and carry it out in the morning when the fish are not floating at the surface. The operation of seining and driving the fish must be slow to avoid injuring the fry. When closing the net, do not let the fish stick to the net. After the fish enter the box, the box should be washed immediately to wash away the excretions and dirt clogging the mesh, so that the water body inside the box is connected with the outside, preventing fry death due to oxygen deficiency inside the box.
13. Physical and chemical indicators of the water body during the fry rearing period:
1) Organic matter oxygen consumption: When the dissolved oxygen in the pond water is not deficient, the higher the organic matter oxygen consumption, the higher the survival rate of bighead carp fry. Before the fry are stocked, the organic matter oxygen consumption should be above 30 mg/L to ensure the fertility needed for plankton growth.
After the fry are stocked, they consume large amounts of plankton and continuously consume organic matter, so fertilization must continue. Fertilization should be in small amounts and frequent, once every 2-3 days. Part of the splashed soybean milk cultivates zooplankton, part becomes organic fertilizer, and only a small part is directly utilized by the bighead carp fry.
2) Dissolved oxygen content: The dissolved oxygen in the water is closely related to the survival of the fry. When the dissolved oxygen in the water drops below 2 mg/L, the fry will show floating head. The dissolved oxygen content in the water body required for normal growth and development of bighead carp fry is 4.5 mg/L; when it drops to 1.7 mg/L, the respiration of the fry is inhibited. In the production process, from before dawn to 1-2 hours after sunrise, if bighead carp fry show slight floating-head behavior, it indicates the water is too fertile, and feeding and fertilization should be stopped.
3) pH value: When quicklime is used for pond clearing, the pH value and hardness of the pond water are both relatively high, and the rotifers all die, but this is harmless to rotifer resting eggs; only when the pH value drops below 10 can the rotifer resting eggs hatch in large numbers. 8-10 days after pond clearing, the lime efficacy disappears, the pH drops below 9, phytoplankton begin to reproduce in large numbers, and the dissolved oxygen content in the pond water rises, often reaching a saturated state. At this time, rotifers appear in large numbers, and the fry should be stocked into the pond in time.
Rearing of One-Year-Old Large-Size Bighead Carp Fingerlings
The process of rearing summer fry with a body length of 2.5-3.3 cm into one-year-old large-size fingerlings with a body length of 20-25 cm is called one-year-old large-size fingerling rearing. It adopts the method of supplementary stocking, generally stocking 600-1,200 summer fry of 2.5-3 cm per mu.
1. Preparatory work before stocking: The fingerling pond is required to be relatively large, generally 10-15 mu, with relatively deep water, generally 1.8-2.5 m. Before stocking, organic fertilizer should be applied for cultivation; for bighead carp, the base fertilizer should be applied in an appropriate amount, and stocking should be done at the peak of rotifers.
2. Summer fry stocking: The stocking time is generally May-June. The stocking methods include monoculture and polyculture; polyculture is generally adopted, because at this stage the habits of the fish gradually show differences, and their requirements for the external environment also differ. By matching and polyculturing according to the different habits of various fish and their adaptability to water quality, not only is a suitable growth environment given to various fish, but the utilization rate of the water body and the relatively economical use of feed are also fully brought into play. Fingerling ponds generally have 2-3 species in polyculture, with a small number of silver carp and common carp stocked together.
3. Feeding management: At this time, bighead carp still mainly feeds on plankton, the pond water is required to be fertile, and the plankton biomass should be high. In addition to applying base fertilizer before stocking, green manure and decomposed manure should also be applied after the summer fry are stocked, combined with regular addition of fresh water to keep the water brownish-green. When feeding, artificial feeding should follow the "four fixed" principles of fixed time, fixed location, fixed quality and fixed quantity, so as to improve feed utilization and reduce the feed conversion ratio; at this time the feeding amount should be relatively small.
Transport of Fry and Fingerlings
In the process of transporting bream and grass carp 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 are robust, the swim bladder is inflated (long waist spot), the mouthparts are open, and they swim actively, so they can be loaded for transport. The loading amount for oxygenated nylon bag transport is about 80% of the transport box.
2. The water quality is fresh and non-toxic, with high dissolved oxygen. Water from rivers, lakes, reservoirs and ponds can all be used; colorless, transparent water with low mud content should be selected. Tap water must be dechlorinated and left to stand for 24 hours before use. In summer, cool water should be used.
3. Before the fingerlings are transported, the fish body must undergo seining training to expel feces. Only when the body is sturdy and mucus secretion is reduced can the survival rate be improved.
4. Pay attention to temperature balance; the temperature difference must not exceed ±2°C. After arriving at the destination, the fish should first be placed in a box to revive; one hour later, feed the fry cooked egg yolk. Feed one egg yolk per 100,000 fry; after seeing the flower intestine of the fry (swallowing egg yolk into the intestine), wait another hour before releasing the fish into the pond. For fry in nylon bags and transport boxes, before putting them into the box, first place them in the water so that the internal and external water temperatures are consistent. Then open the nylon bag or transport box, pour in pond water, place the bag into the box, and let the fry (fingerlings) swim out on their own.