Breeding Techniques for Summer Fry and Larger Fingerlings of Bream
Pond Selection
The 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 pond bottom, loam soil, a silt thickness of 15-20 cm, and convenient water inlet and drainage.
The fingerling rearing pond has an area of 6-10 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 pond bottom, loam soil, a silt thickness of 15-20 cm, and convenient water inlet and drainage.
Pond Clearing and Elimination 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, 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, which has a certain effect on increasing the survival rate of fry and fingerlings.
1. Pond clearing with quicklime: 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. Pond clearing with tea seed cake
At a water depth of 1 m, use 80 jin per 1 mu, applied 10-15 days before the fry are stocked. When the water temperature is low, the toxicity disappears slowly; when the temperature is high, it disappears quickly. First break the tea seed cake into pieces, put them into a wooden bucket or water vat, add water to soak; at a water temperature of 25°C, soak for one day and night before use. When applying, add a large amount of water and splash evenly over the whole pond.
3. Pond clearing with bleaching powder: At a water depth of 1 m, use 25-30 jin of bleaching powder per mu; after dissolving the bleaching powder in water, 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 pond clearing with bleaching powder. Pond clearing with bleaching powder is related to the fertility of the pond water, and the effect is poor in fertile water.
Fry Rearing
The water-fry fry 3-4 days after hatching are called larvae, also known as fry; when reared to 1.5-2 cm they are juvenile fish, called wuzai in production; when reared to 2.5-3.3 cm they are juvenile fish, called cunpian, huopian and summer fry in production.
1. Pond fertilization to enrich water quality: The role of fertilization is to cultivate various types of plankton in the water as the opening feed for fry after they are stocked. 4-5 days after disinfection and elimination of wild fish, or 5-7 days before the fry are stocked, 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, rotifers and plankton reach their peak of reproduction.
Fertilization effect: After pond fertilization, the dominant populations of plankton that first appear are related to the nature of the fertilizer. When organic fertilizer is applied, phytoplankton - such as chrysophytes and cryptomonads - and zooplankton - such as stichotrichs and peritrichs - first appear in large numbers. When inorganic fertilizer is applied, diatoms, scenodesmus and halteria become the main populations.
When the amount of fertilizer applied is large, some species of green algae and blue-green algae will develop in large numbers; when the amount of fertilizer applied is small, many species of diatoms, such as spindle-shaped diatoms and disc-shaped diatoms, become the dominant species.
4-5 days after fertilization, zooplankton can reach their peak. The zooplankton that first appear in large numbers are protozoa and rotifers, then cladocerans, and then copepods.
After pond fertilization, if the pond water is light greenish-brown and algae, protozoa and rotifers in the pond reproduce in large numbers while cladocerans have just begun to appear, this is most suitable for the growth of bream fry.
2. Time for stocking fry: Bream water-fry fry should be stocked on the 4th-5th day after fertilization, when rotifers and cladocerans are at their peak occurrence.
3. Regulate water quality and control the increase of large zooplankton: As the water gradually becomes more fertile, large zooplankton increase accordingly. Bream fry are delicate, and the pond water should not be too fertile when the fry are stocked.
4. Fry stocking: Bream fry are slender and delicate; when stocking, the fertility should be moderate, not too fertile. Before stocking, place the larvae first in a fry box and feed 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) Cook the egg yolk a little longer, wrap the egg yolk in 60-mesh nylon sieve cloth, and beat and rinse it in a basin of water to filter it; do not squeeze it with your hands, so that fine yolk particles pass out through the mesh into the water;
2) Use your fingers to evenly sprinkle the egg yolk water into the fry box; after half an hour, yolk particles can be seen in the intestines of the bream larvae (commonly known as flower intestine);
3) After keeping them in the fry box for 3-4 hours, release the larvae into the pond.
5. Stocking density: The general stocking density is 100,000-150,000 fry per mu. If the fry grow to a total length of 2-2.5 cm and are seined and divided into ponds, the stocking density can be increased, reaching 150,000-200,000 fry per mu.
6. Fry feeding: After bream larvae are stocked in the pond, on the 1st day they are fed soybean milk, with 2-3 jin per day of soybean milk made from soybeans per 100,000 fry, water:beans = 30:1, fed three times a day, at 9 a.m., 1 p.m. and 4 p.m. When grinding soybean milk, the soybeans must be soaked until swollen, and after grinding the okara must be removed. When feeding, sprinkle the milk along the pond edge for two rounds, and make the sprinkled milk resemble raindrops, evenly distributed.
After 10 days of feeding, switch to soybean cake milk. Crush the soybean cake, soak it in water for 3-4 hours, then grind it into soybean cake milk with a soybean cake-to-water ratio of 1:10.
7. Stage-wise water addition: Add new water to the pond in stages to raise the pond water level, so as to increase the oxygen content in the water, improve water quality, expand the activity space for bream fry, and accelerate fish growth. It also promotes plankton reproduction and increases live feed.
The amount and frequency of water addition should be determined according to specific conditions. Generally, one week after the larvae are stocked in the pond, carry out the first water addition. After that, add water once every 4-5 days. Add about 20 cm each time, and finally raise the water depth to 1.0-1.2 m.
8. Pond patrol management: After the larvae are stocked in the pond, patrol the pond three times a day, carrying out the "three checks" and "three diligences."
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 water quality, diligently keep records, and arrange the next day's feeding, fertilization and water addition. At all times pay attention to checking for the occurrence of diseases and carry out timely prevention and treatment.
9. Training and pond division: After 20-25 days of rearing, when the bream larvae have grown to about 3 cm, they should be divided for rearing. Before summer fry are removed from the pond, they must undergo 2-3 rounds of seine training. This enables the fingerlings, in the process of being concentrated, to increase their adaptability to low oxygen. It makes the fish body "hardened" and sturdy, able to withstand removal from the pond for division and rearing, and avoids producing large amounts of mucus and feces during transport that would pollute the water quality, thereby increasing the survival rate during transport. Seine training can also remove harmful organisms and estimate the number of summer fry.
1) First seining: Gather the bream summer fry in the net, check their physique, and then immediately release them back into the pond. Because the fish body is tender, operations must be careful.
2) Second seining: After an interval of 1 day, carry out the second seining training. After gathering the fish, 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 reared on site, then after two rounds of seining and concentration in the box, they can be divided for rearing.
3) Third seining: After the second seining, after another 1 day, carry out the third seining, place the fingerlings in a net box in a pond with clearer water and "hang-rear" them for 1 night; the next morning they can be loaded for long-distance transport.
For training bream fry, be sure to choose fine weather and carry out the work 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 excretions and dirt clogging the mesh, so that the water inside the box circulates freely with the outside, preventing fry death due to oxygen deficiency inside the box.
10. Physical and chemical indicators of water during fry rearing:
1) Organic matter oxygen consumption: When dissolved oxygen in the pond water is not deficient, the higher the organic matter oxygen consumption, the higher the survival rate of bream fry. Before the fry are stocked, the organic matter oxygen consumption must 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 use up organic matter, so fertilization must continue. Fertilization should be in small amounts and high frequency, once every 2-3 days. Part of the sprinkled soybean milk cultivates zooplankton, part becomes organic fertilizer, and only a small part is directly utilized by the bream fry.
2) Dissolved oxygen: The dissolved oxygen in water is closely related to the survival of fry. When dissolved oxygen in the water drops below 2 mg/L, the fry will show floating-head behavior. The dissolved oxygen level required for normal growth and development of bream fry is 5.5 mg/L; when it drops to 1.7 mg/L, the respiration of the fry is inhibited. In production, if bream fry show slight floating-head behavior from before dawn to 1-2 hours after sunrise, it indicates the water is too fertile, and feeding and fertilization should be stopped.
3) pH value: When quicklime is used to clear the pond, both the pH value and hardness of the pond water are relatively high, and rotifers die, but this is harmless to rotifer resting eggs. Only when the pH drops below 10 can rotifer resting eggs hatch in large numbers. 8-10 days after pond clearing, the effectiveness of the lime disappears, the pH drops below 9, phytoplankton begins to reproduce in large numbers, and the dissolved oxygen in the pond water rises, often reaching saturation. At this time, rotifers appear in large numbers, and the fry should be stocked in the pond in good time.
Rearing of One-Year-Old Bream Fingerlings
The process of rearing summer fry with a body length of 2.5-3 cm into fingerlings with a body length of 12-15 cm is called fingerling rearing, and the process can be divided into 2 rearing stages:
First-level rearing stage: Rearing summer fry with a body length of 2.5-3 cm into 4-5 cm summer fry is called the first-level rearing stage.
Second-level rearing stage: Rearing summer fry with a body length of 4-5 cm into fingerlings 12-15 cm long is called the second-level rearing stage.
1. First-level rearing stage: Rearing bream huopian into 1.2-1.5 cun (total length 4-5 cm) summer fry, with 30,000 3 cm total-length huopian stocked per mu. A single-species rearing method is adopted.
1) Artificial feeding: For first-level rearing of 3 cm bream huopian, relying on natural food is not enough, and soybean cake milk must be fed. The method for making soybean cake milk is to use 1 jin of dry soybean cake per 10,000 fry, soak it for 4-5 hours, and then grind it into milk with a ratio of 4 parts water to 1 part soybean cake. When feeding, choose one side of a shallow pond and place the feed in small piles on the pond slope about 30 cm below the water surface, with 2 m between each pile and 2 jin per pile. This is called the "du tan" feeding method, fed once every morning. In the afternoon, feed 10 jin of duckweed (wuping); apply 100 jin of mixed compost per 1 mu per day, and increase or decrease according to the fertility of the water.
2) Adding new water: Once a week, add new water to a depth of 10 cm; after 20 days, the bream summer fry have already reached 5 cm, and after seining training of the fish body, they enter the second-level rearing stage, that is, final rearing.
2. Second-level rearing stage: Rearing summer fry into 4-5 cun (12-15 cm) winter fingerlings or spring fingerlings; during this period a mixed rearing method is adopted, with a relatively large pond area of 6-10 mu and a water depth of 1.8-2.0 m.
1) Main fish rearing: Bream summer fingerlings with a body length of 4 cm can already swallow formulated pellet feed. A method of rearing with bream as the main species, silver crucian carp as a companion species, and silver carp and bighead carp as incidental species can be adopted.
2) Rearing management: Bream summer fry are stocked in clear water; on the 2nd day, soybean cake milk is fed at fixed points to attract the fish to feed. One week later, when the fish have grown to 5 cm, 1.5 mm pellet feed is broadcast, adopting the five-fixed operation method:
Fixed person: Dedicated management. One person manages 3-5 ponds, with an area of about 30-40 mu.
Fixed time: Determine the number of feedings according to temperature changes; the higher the temperature, the more feedings. Start feeding attraction at a water temperature of 15°C; at 20-24°C feed twice a day; at 25-28°C feed three times a day; above 28°C feed four times a day, with an interval of 3 hours.
Fixed point: Choose the center of the deep side of the fish pond and extend 2-3 m into the pond to build a feeding platform; use the striking of iron as the first signal to train feeding and attract the fish to float up and compete for food. Broadcast from right to left in an arc, finishing within 30 minutes and stopping when the school of fish leaves.
Fixed quality: The feed must be fresh, with a crude protein content of 30%. In the later growth stage, the crude protein content of the feed is 26%.
Fixed quantity: Formulate the daily feeding rate according to temperature changes.
3) Frequent observation, prevention of floating-head behavior, and prevention of fish diseases: 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, or turn on the aerator to regulate water quality.
Weather changes affect the growth and feeding of bream fingerlings, and feeding should be increased or decreased as appropriate according to weather changes. In the morning, when the temperature is low and dissolved oxygen in the water is low, reduce the feeding amount; at noon when the weather is clear, feed more. Do not let them eat too full in the evening. When dissolved oxygen in the water is below 3 mg/L, the fish only eat feed but do not gain flesh.
Bream rarely get sick, but they may be "dragged in" when silver crucian carp suffer from hemorrhagic disease, and they also become diseased together with silver carp. During pond patrols, pay attention to fish swimming alone away from the school; once this appears, splash chlorine dioxide over the whole pond, and splashing twice in 3 days can stop it.
Rearing of Two-Year-Old Bream Fingerlings
For the rearing of two-year-old bream fingerlings, a mixed stocking method of the main fish with other fish should be adopted, feeding full-price pellet feed. The fish pond is 6-10 mu, with a water depth of 1.8-2.0 m, convenient water inlet and drainage, and a good water source. In fish ponds after pond clearing and disinfection, stock one-year-old bream fingerlings in winter, with silver crucian carp as companion fish and silver carp, bighead carp and xenocypris as incidental fish.
1. Rearing management: Feed full-price pellet feed to induce bream fingerlings to gather and float up to compete for food. Feed according to the daily water temperature and the formulated daily feeding rate, adopting the five-fixed work method.
2. Use of aerators: Starting in May-June, on clear days at noon turn on the aerator for 1-2 hours (from 12:00 to 14:00), and before dawn turn on the aerator for 1-3 hours (from 4:00 to 7:00), turning it off half an hour after sunrise.
If the weather is bad and muggy, during pond patrols clap your hands to startle the pond fish. If fish make sounds in the center of the pond after being startled, the aerator should be turned on immediately to prevent oxygen deficiency and pond turnover causing fish death. In July-August, when the weather is hot, new water should be frequently added.
Transport of Fry and Fingerlings
In the process of transporting bream fry and fingerlings, no matter what method is used, operations must be meticulous, paying attention to the following aspects:
1. The fry should be robust in physique, with the swim bladder inflated (long waist point) and the mouthparts open, and swimming actively, before they can be loaded for transport. For transport in oxygen-filled nylon bags, the loading amount is about 80% of that of a transport box.
2. The water 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 fingerlings are shipped, the fish body must undergo seine 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, first place them in a box to revive the fish; one hour later feed the fry cooked egg yolk. Feed one egg yolk per 100,000 fry, and 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 placing them in the box, first put them into the water so that the inside and outside water temperatures are consistent. Then open the nylon bag or transport box, pour in pond water, place the bag in the box, and let the fry (fingerlings) swim out on their own.
Quality Identification of One-Year-Old Fingerlings
Use the "four looks" method to identify the quality of bream fingerlings.
1. See whether the size of the fingerlings removed from the pond is uniform: Fingerlings removed from the pond should be uniform in size and robust in physique. If individual sizes are uneven, the population survival rate will inevitably be lower. Small individuals are thin and weak, commonly called "biezi," and should be concentrated and reared separately.
2. Look at body color: Commonly called looking at "fleshiness." High-quality bream fingerlings are silvery-gray and translucent, with silvery-white sides and belly and obvious stripes on the sides of the body.
3. Look at the body surface: High-quality bream fry and fingerlings have a glossy body surface, with a thin layer of mucus protecting the scales and skin.
4. Look at swimming behavior: High-quality bream fingerlings swim actively and have strong upstreaming ability, and when concentrated in the net their heads point downward.