Detailed Explanation of Key Points in Pengze Crucian Carp Farming Techniques

Pengze crucian carp, also known as the reed-flower crucian carp, belongs to the order Cypriniformes, subfamily Cyprininae, genus Carassius, and originated in Pengze County, Jiangxi Province. Pengze crucian carp has the advantages of large individual size, fast growth, omnivorous feeding habits, strong stress resistance, few diseases, tender meat, and high nutritional value. Combined with simple breeding techniques, convenient management, low investment, and good returns, it is deeply welcomed by farmers and consumers.
　　
I. Ecological Habits
1. Morphological characteristics: The Pengze crucian carp has a spindle-shaped body, a relatively small head, a relatively thick back, a grayish-black dorsal body color, a grayish-white belly, bluish-black fin rays, and a gently curved line from the bottom of the lower jaw to the lower edge of the pectoral fin.
2. Living habits: The Pengze crucian carp is a eurythermal fish that prefers benthic life. Its main growing season is from April to November, with the fastest growth from July to September. The Pengze crucian carp has a wide adaptive range for water temperature. At a water temperature of around 4°C, more than 80% of the fish will still feed in small amounts, and it can live well even under ice-covered water. The optimum growth temperature for Pengze crucian carp is 25-30°C, and water temperatures as high as 38°C do not affect its survival. The Pengze crucian carp is a large crucian carp, with common individuals weighing more than 250 g. After 8-10 months of growth, its body weight can reach more than 100-150 g.
3. Reproductive habits: The Pengze crucian carp can spawn not only in rivers and lakes but also in still-water ponds. Pengze crucian carp bred in spring or summer can develop their gonads to stage IV by the end of autumn of the same year. Under natural conditions, the Pengze crucian carp is a multiple-spawning type. The breeding season is from March to July. When the spring water temperature rises to 17°C, spawning and reproduction begin, and reproductive activity is most intense at water temperatures of 20-25°C. Fertilized eggs can hatch into fry after about 53 hours at a water temperature of 18-20°C; the higher the water temperature, the shorter the hatching time. The time required for fry from hatching to horizontal swimming is roughly similar to the hatching time.
　　
II. Breeding Techniques
1. Source and cultivation of broodstock. Pengze crucian carp broodstock comes from 1-2 year old adult fish from mixed culture in adult fish ponds or intercropping in fry ponds. The selected broodstock should require females to be more than 200 g and males to be more than 150 g, conform to morphological standards, be robust, and be free of disease and injury. The selected broodstock should be cultivated in a dedicated pond for overwintering. The overwintering pond should be sheltered from the wind and face the sun, with an area of about 1 mu and a water depth of about 2 m. During the overwintering period, if the weather is clear and fine, refined feed should be fed at about 2% of the fish body weight. After the beginning of spring, male and female broodstock should be separated into different ponds for cultivation in a timely manner. After separation, management should be strengthened, the amount of feed should be appropriately increased, pond inspections should be carried out frequently, and changes in water temperature and water quality should be observed.
2. Identification of male and female fish. For sex identification of Pengze crucian carp, in the non-reproductive season, if the tip of the pectoral fin is long and its end reaches the base of the pelvic fin, it is a male; if it does not reach, it is a female. In the reproductive season, besides this, there are other identification methods: females have smooth and soft body surface, a relatively plump body shape, obvious ovarian outline, and eggs can often be squeezed out by pressing the lower abdomen. Males have nuptial tubercles on the head and pectoral fins, a rough body surface to the touch, a relatively sunken abdomen, and milky-white fluid flows out when the abdomen is gently pressed.
3. Preparatory work before induced spawning. Select a pond of 0.6-1 mu as the broodstock spawning pond. 8-10 days before induced spawning, the spawning pond should be cleared and disinfected, then filled with water to about 70 cm for later use. When filling with water, it should be filtered through fine sieve silk. Spawning nests are made by tying palm bark or willow roots. Before use, they should be soaked and disinfected in 10-20 parts per ten thousand potassium permanganate or 1/5 000 malachite green solution, then dried in the sun for later use. Prepare induced spawning agents in advance. Commonly used agents include human chorionic gonadotropin (HCG), luteinizing hormone-releasing hormone analog (LRH-A), fish pituitary gland (PG), and others.
4. Artificial induced spawning. When the water temperature rises to 17°C, artificial induced spawning can be carried out on clear days. For induced spawning, selected male and female broodstock are paired at a ratio of 3:1, and a single injection is administered between the bases of the pectoral fins. The injection dose is generally 800-1 000 international units of HCG per kilogram of female fish, or 20-30 micrograms of LRH-A, or 2-3 PG, while other drugs are used for induced spawning according to the instructions, and the injection dose for male fish is halved. The above drugs can be used alone or in combination of two or more, with relatively good results. The best injection time is from 3 to 5 p.m., so that the broodstock can spawn the next morning. Spawning nests should be placed in the evening of the day of injection.
5. Hatching. At a water temperature of 18-20°C, the induced spawning time is 9-16 hours, and the spawning process of the entire group lasts 6-20 hours. The broodstock's courtship chasing often occurs below the water surface, with relatively little water disturbance and splashing sound. After spawning, Pengze crucian carp will eat the eggs, so after spawning is completed, spawning nests covered with fertilized eggs should be moved to a hatching pond for hatching in a timely manner. The hatching pond should preferably have an area of about 1 mu and a water depth of about 0.6 m. It should be cleared and disinfected in advance and filled with fresh water. Generally, 200 000-300 000 fertilized eggs are placed per mu. At a water temperature of 18-20°C, fry can hatch in about 50-55 hours. After hatching, the spawning nests can be removed after 3-4 days.
　　
III. Fry and Fingerling Cultivation
The fry and fingerling cultivation of Pengze crucian carp is divided into the summer-fry cultivation stage and the winter-fingerling cultivation stage.
1. Summer-fry cultivation. The stocking density of fry is generally 150 000-200 000 per mu. When placing fertilized eggs, a rough estimate can be made based on an 80% hatching rate.
When the fry begin to hatch, some fermented organic fertilizer can be applied in the pond to cultivate water quality, so that when the fry begin to feed, there will already be large amounts of rotifers and other plankton in the pond as suitable food for the fry. 2-3 days after hatching, cooked egg yolk or soybean milk should be fed in a timely manner. 4-5 days after hatching, feed twice a day by splashing around the perimeter. Generally, 1.5-2.5 kg of soybeans are ground into milk per 100 000 fry per day. As the fry grow, gradually increase the amount of feed and fertilizer, shifting from splashing around the perimeter to splashing over the whole pond. During the summer-fry cultivation stage, add fresh water once every 5-7 days, adding 10-15 cm of water. After 20-30 days of cultivation, the fry can grow to about 3 cm, at which point they can be divided among ponds or sold. Before pond division or sale, 2 rounds of net-pulling exercise should be carried out. At present, summer-fry fingerlings are often directly stocked in ponds for intercropping, and market size can be reached in the same year. Therefore, summer-fry cultivation can adopt the method of rapid growth through sparse stocking, with 80 000-100 000 fry per mu. Summer-fry fingerlings produced in this way are uniform in size at harvest, have a high survival rate, and can be harvested about 10 days earlier.
2. Winter-fingerling cultivation. Summer fry cultivated to about 3 cm can be transferred to the winter-fingerling cultivation stage. One week before stocking, the fingerling pond should be cleared and disinfected. The fingerling pond should have an area of 1-3 mu, with 20 000-30 000 summer-fry fingerlings stocked per mu, and 1 000-1 500 summer-fry fingerlings of silver carp and bighead carp can also be added. Winter-fingerling cultivation is mainly based on feeding feed, with fertilization as a supplement. Daily management is similar to that for winter fingerlings of other domestic fish. In the middle of cultivation, the growth of fingerlings should be checked frequently. When the weather turns cold and the water temperature drops, they can be combined into ponds for overwintering. The overwintering pond should stock 40 000-50 000 fingerlings per mu. During the overwintering period, when the weather is clear and fine, refined feed should be appropriately fed to ensure that the fingerlings are robust and to increase the survival rate.
　　
IV. Adult Fish Farming The adult fish farming of Pengze crucian carp mostly adopts the form of mixed culture.
1. Intercropping in grass carp and silver carp fingerling ponds. Without reducing the stocking density of summer-fry fingerlings of grass carp and silver carp, 150-200 summer-fry fingerlings of Pengze crucian carp are intercropped per mu. Under normal feeding and management conditions, after 5-6 months of cultivation, the harvest size of Pengze crucian carp can reach 200 g, with the largest individual reaching 310 g, and 20-40 kg of adult Pengze crucian carp can be increased per mu.
2. Intercropping in adult fish ponds of grass carp, silver carp, bighead carp, and common carp. Stocking summer-fry fingerlings of Pengze crucian carp directly into adult fish ponds to grow into adult fish is an effective measure to increase production. Stocking 200 3 cm fingerlings per mu, after 6 months of cultivation, the average size can reach 180 g, and it does not affect the stocking of other fish.
3. Pond main culture. Stock 1 500 winter-fingerlings of Pengze crucian carp per mu, with 600-700 grass carp, silver carp, and bighead carp as supplementary species, mainly feeding refined feed. After 5-6 months of cultivation, about 300 kg of Pengze crucian carp with a size of more than 200 g and about 150 kg of grass carp, silver carp, and bighead carp can be harvested. Stock 2 000 summer-fry fingerlings of Pengze crucian carp per mu, and at harvest the size of Pengze crucian carp can reach 100-150 g.
4. Cage culture. Use floating cages of 16-28 sq m, stocking 50-200 Pengze crucian carp of more than 5 cm per sq m, feeding pelleted feed for common carp, 4-6 times a day. After 100 days of cultivation, they can grow to 100 g, and after 200 days they can grow to about 250 g.
Pengze crucian carp is also suitable for intercropping in domestic fish broodstock ponds, mixed culture in small lakes and reservoirs, or stocking in rice fields.
　　
V. Diseases and Their Prevention and Treatment
As a new artificially selected breeding variety, the strong disease resistance of Pengze crucian carp is one of its main excellent traits. In many years of breeding experiments and large-area (tens of thousands of mu) aquaculture production, there has not yet been a single case of mass death of Pengze crucian carp due to infection with a certain fish disease, nor has there been any outbreak of fish disease. Practice has proved that Pengze crucian carp has an extremely low infection rate for various diseases. Even after infection, the survival rate will not be greatly affected; only the growth rate or appearance of the diseased fish is affected.
The common diseases of Pengze crucian carp are fish diseases caused by animal pathogens on the body surface, such as saprolegniasis and bacterial gill-rot disease.
1. Bacterial gill-rot disease: Bacterial gill-rot disease has occurred in caged Pengze crucian carp. Diseased fish move slowly, have a darkened body color, and often swim alone away from the group at the water surface. The inner epidermis of the operculum of diseased fish is corroded into round transparent areas, commonly known as “open skylight”. The ends of the gill filaments turn white and rot and are adhered to by floating mud, which the public calls “dragging mud”. In severe cases, the gill filament cartilage is exposed, and death finally occurs due to difficulty in breathing. The pathogen is Flavobacterium columnare, and the epidemic season is from May to September. This disease can cause sporadic deaths of Pengze crucian carp.
Prevention and treatment methods: During the epidemic season or during the outbreak period, persistently hang baskets with bleaching powder or salt. After treatment, this disease can show results in about one week.
2. Saprolegniasis. Saprolegniasis occurs only in the fertilized egg hatching stage and the fry stage of Pengze crucian carp. The pathogens are Saprolegnia, Achlya, Leptolegnia, and Aphanomyces in the family Saprolegniaceae. The epidemic season is from March to May.
During the fish egg hatching process, due to climate and water temperature, Pengze crucian carp eggs are greatly harmed by saprolegniasis. In infected fish eggs, hyphae invade the egg membrane like root-like structures and grow on the outside of the egg membrane. In severe cases, this causes mass death of fish eggs.
At the fry stage, due to careless handling during netting and transport, scales are rubbed off, or parasites damage the skin, so that mold invades the wound. When visible to the naked eye, the hyphae have already penetrated inward into the muscle, spread and expanded, and grown outward into cottony hyphae, so it is called “growing hair”. Diseased fish appear burdened by the body and float at the water surface, swim abnormally, have reduced appetite, and finally die from emaciation.
Prevention and treatment methods: Thorough pond clearing and disinfection (preferably with quicklime) can generally effectively prevent saprolegniasis.
During the fry hatching stage, it is more important to choose suitable induced spawning weather and water temperature. For induced spawning of Pengze crucian carp, be sure to avoid cold waves and rainy weather. Generally, induced spawning should be carried out only when the water temperature is 17°C and it is expected that there will be 4-5 days of clear and warm weather after induced spawning. In addition, more spawning nests should be set up so that the fish eggs are not too dense. This can effectively prevent or reduce the occurrence and severity of saprolegniasis.
3. Trichodiniasis. Trichodiniasis mainly occurs during the summer-fry fingerling cultivation stage of Pengze crucian carp. The epidemic season is from May to August, with the peak period from June to July. The pathogen is Trichodina. After the body surface or gills of diseased fish are stimulated by the pathogen, they secrete large amounts of mucus, and the tissues suffer severe damage. Diseased fish become emaciated, swim slowly, intermittently swim on their sides, and have difficulty breathing. They often swim in groups at the pond edge and can cause a relatively large number of deaths. Generally, this disease is most likely to occur in fish ponds that are small in area, shallow in water, and have high stocking density.
Prevention and treatment methods: Splash the whole pond with a mixture of copper sulfate and ferrous sulfate (ratio 5:2) to make the pond water concentration 0.7 parts per ten thousand. Or use copper sulfate alone. The application method is preferably the two-time method. The first application makes the pond water concentration 0.4-0.5 parts per ten thousand, and after 3 days a second application is made to make the pond water concentration 0.3 parts per ten thousand. Generally, results can be seen 3 days after application.
4. Argulosis. This disease occurs in both the winter-fingerling cultivation stage and the adult fish farming stage of Pengze crucian carp, and infection can occur throughout the year. The pathogen is Argulus. The symptoms of diseased fish are extreme restlessness, rapid frantic swimming, and jumping and swimming on their sides, and Argulus can be seen on the fish body with the naked eye. Argulosis generally does not cause death of Pengze crucian carp, but it can seriously affect the growth of Pengze crucian carp.
Prevention and treatment methods: At the beginning of the epidemic, splash crystalline trichlorfon over the whole pond once at a concentration of 0.25-0.5 parts per ten thousand.
5. Lernaeosis This disease has only appeared in the adult fish stage of Pengze crucian carp, with the disease season from April to October. The pathogens are various species of Lernaea, parasitic on the body surface or in the oral cavity (very few) of the fish.
Lernaeosis generally does not cause death of Pengze crucian carp. In the early stage of the disease, diseased fish appear restless and anxious, intermittently swim on their sides, have reduced appetite, and become emaciated, seriously hindering fish growth. Lernaea uses its head horns to drill into the host's muscle or under the scales, causing redness, swelling, or necrosis of surrounding tissues. A small number of diseased fish will also be infected with saprolegniasis at the same time, thus causing death.
Prevention and treatment methods: During the disease season, splash crystalline trichlorfon over the whole pond at a concentration of 0.2-0.3 parts per ten thousand, once every half month, for 2-3 consecutive times.
Treatment method: Splash crystalline trichlorfon over the whole pond to make the pond water concentration 0.5 parts per ten thousand, and use it again after 1 week; or soak the fish body in 0.025 parts per ten thousand potassium permanganate solution for 20-30 minutes.