High-yield and high-efficiency technology for two-season-per-year pond monoculture of grass carp
Pond monoculture of grass carp is one of the main aquaculture models in the freshwater fishery of Sha County, most of which belongs to traditional conventional culture, with small stocking size, long culture cycle, insufficient investment in aquaculture equipment, high labor intensity and low yield, generally 400kg-750kg per mu, with annual profit of about 1000 yuan/mu, and relatively low economic benefit. In order to improve pond aquaculture yield and economic benefit, in 2006 the author carried out a demonstration of high-yield and high-efficiency aquaculture technology for two-season-per-year pond monoculture of grass carp, mainly adopting measures such as stocking large-size fingerlings, reducing the stocking amount of low-quality fish, expanding the stocking number of famous and superior varieties, equipping automatic feeders and aerators and other aquaculture equipment, injecting grass carp with freeze-dried cell attenuated vaccine and “triple” vaccine to increase the survival rate, promoting the feeding of complete-price pelleted feed, stocking twice a year, and draining and harvesting twice, developing from the traditional extensive culture type toward intensive and industrialized aquaculture, and promoting the planting of forage grass, using wasteland, idle winter fields and pond ridges to plant high-quality grasses such as ryegrass, napier grass and sudan grass to feed grass carp and supplement the shortage of green feed in the off-season. Over 1 year, the demonstration and extension pond area at the Sha County freshwater aquaculture farm was 156 mu, with an average yield of 1602.7kg per mu.
I. Pond conditions
The aquaculture demonstration ponds covered an area of 156 mu, totaling 18 ponds, each pond with an area of 5 mu-13 mu, a water depth of 1.9m-2.5m, sufficient water source, fresh and pollution-free water quality, convenient drainage and irrigation of the ponds, sufficient equipped electric power, and convenient transportation.
II. Aquaculture machinery
For water surfaces of 3 mu-5 mu, 1 aerator with a power of 3kW was equipped, and each pond was equipped with 1 automatic feeder. The aerator and feeder used microcomputer automatic control of aeration time and feeding time.
III. Supporting fingerling ponds
A 5-mu adult fish pond was supported by 1 mu of fingerling pond, so as to cultivate large-size fingerlings and ensure a sufficient source of large-size fingerlings.
IV. Pond disinfection
7 days-10 days before the fingerlings were put into the pond, the pond was filled with water to a depth of 1m, and bleaching powder containing 30% chlorine was splashed over the whole pond with the water at 7kg/mu-10kg/mu for disinfection.
V. Fingerling stocking
The stocking time for the first season was January, with an average stocking of 270 large-size grass carp fingerlings per mu at a size of 250g/fish-350g/fish, 60 silver carp per mu at a size of 150g/fish, 30 bighead carp per mu at a size of 150g/fish, and 54 Jian carp per mu at a size of 250g/fish; the stocking time for the second season was June, with an average stocking of 540 grass carp fingerlings per mu at a size of 150g/fish-200g/fish, 86 silver carp per mu at a size of 100g/fish, 36 bighead carp per mu at a size of 100g/fish, 143 Jian carp per mu at a size of 15g/fish-20g/fish, and 20 largemouth catfish per mu at a size of 15g/fish.
VI. Vaccine injection
In order to improve the survival rate of grass carp culture, all stocked grass carp fingerlings were injected with freeze-dried cell attenuated vaccine and triple “three diseases” vaccine. The vaccine injection method was as follows: when stocking grass carp fingerlings, a large wooden barrel for holding fish (or a large plastic basin) was prepared beside the pond, and in the barrel a medicinal solution was prepared at a dosage ratio of 80g of 90% crystalline trichlorfon and 0.8kg of table salt added to 50kg of water; grass carp were put into the container in batches for disinfection and anesthesia, and the freeze-dried cell attenuated vaccine powder was diluted with “triple” vaccine liquid (at 1:1) for preparation; each grass carp was injected with 0.3mL, the injection site was the base of the dorsal fin, the needle entry angle was 45°, and the injection depth was about 0.5cm.
VII. Feeding management
1. Feed feeding adopted a feeding method organically combining compounded pelleted feed and green feed. Each pond was provided with 1 feed platform. In the early stage of culture, when the water temperature was 15℃-22℃, feeding was mainly artificially planted ryegrass, supplemented by pelleted feed; when the water temperature was normally stable at 23℃-30℃, feeding was mainly complete-price pelleted feed, supplemented by green feed. Feeding was carried out in the order of first feeding green feed and then feeding pelleted feed, and feeding needed to achieve fixed time, fixed location, fixed quality and fixed quantity. When feeding pelleted feed, feeding domestication work should be done well so that the fish gather and float to the surface to scramble for food; generally the domestication time was 3 days-5 days. In the early stage of culture, the particle size of the pelleted feed was 2.5mm, and in the later stage of culture the particle size of the pelleted feed was 3.5mm. Generally, pelleted feed was fed 2 times a day, with a daily feeding rate of 3.5%-5%. When feeding green feed, 10kg-15kg of green feed was fed per 50kg of fish body weight. It was appropriate for grass carp to eat until 80% full, and the daily feeding amount was increased or decreased as appropriate according to weather changes and feeding conditions.
2. Water quality regulation In the aquaculture process, because the feed was fed sufficiently, the water quality was relatively fertile; apart from applying sufficient base fertilizer at one time at 200kg/mu-300kg/mu, no additional fertilizer was applied during the aquaculture process. Maintaining good and stable water quality could ensure that the fish pond did not suffer from pond turnover, which was an important part of daily management. It was necessary to persist in patrolling the pond 2 times a day, regularly adding new water 1 time a week, closely paying attention to changes in water quality, and promptly taking effective water quality improvement measures. Water quality management focused on grasping “shallow in spring, full in summer, refreshing in autumn.” “Shallow in spring” means that from late winter to spring when fingerlings had just been stocked, the pond water depth was controlled at 1.0m-1.2m, which was favorable for water temperature to rise; “full in summer” means that summer was the peak growth period for fish, so the pond water should be filled full and moderately flowed to form micro-flowing water, so as to prevent floating head and pond turnover caused by sudden changes in high-temperature weather; “refreshing in autumn” means that in autumn the pond was fully loaded, so water quality should be frequently regulated, with each drainage not exceeding 1/4, to ensure refreshing water quality and high dissolved oxygen content.
3. Daily management Feeding management personnel should conscientiously keep daily records of fingerling stocking amount, feeding amount, fish disease prevention and treatment, and the number of fish deaths. Daily management should achieve “four earlies” (namely early pond clearing, early fertilizing, early stocking, early feeding) and “four looks” (namely looking at the season, looking at the weather, looking at the fish condition, and looking at the water color when feeding feed), and reasonably use the aerator. Starting from summer, the aerator should be turned on; generally the aerator was turned on for 2 hours-3 hours in the early morning every day, turned on from the latter half of the night until dawn on rainy days, and turned on for 1 hour-2 hours at noon on sunny days, so that the pond water reached a relatively high dissolved oxygen content standard.
4. Fish disease prevention and treatment The fish disease occurrence season was generally April-September, with the peak period in May-July. It was necessary to follow the principle of “prevent first when there is no disease, treat early when there is disease” and adopt a method combining ecological prevention, vaccine injection, and prevention and treatment with Chinese and Western medicines. Conscientiously do a good job in pond clearing, consolidation and disinfection before fingerling stocking and disinfection of fingerlings when entering the pond, so as to kill pathogens. Starting from April, quicklime at 10mg/L-20mg/L was splashed once about every 15 days for prevention. May-August was the season when fish diseases were prevalent; 90% crystalline trichlorfon at 0.3mg/L-0.5mg/L could be splashed over the whole pond to prevent and treat parasitic diseases; chlorine dioxide at 0.3mg/L-0.4mg/L or bromochlorohydantoin at 0.3mg/L could be splashed over the whole pond to prevent and treat bacterial diseases. In the later stage of culture, the water quality was very dense and algae proliferated in large amounts, so 0.7ppm copper sulfate could be splashed to kill them.
5. Timely harvesting After 5 months of culture, the various fingerlings stocked in the first season had basically reached commercial size and all needed to be harvested and sold before the end of May. At this time it was around the Dragon Boat Festival, which was the off-season for fresh fish supply, and the market selling price was high. After more than another 5 months of careful culture, the various fingerlings stocked in the second season reached commercial size before the end of December and all needed to be harvested and sold.
VIII. Test results
1. Fishery output The demonstration and extension pond area was 156 mu, and according to harvesting statistics the annual total output of fresh fish was 250.02 tons, among which grass carp output was 184.87 tons, accounting for 73.9% of the total output, and the average survival rate of grass carp reached 95.4%. The average yield per mu was 1602.7kg, with newly added output of 133 tons and an average increase of 852.7kg per mu.
2. Economic benefit The total harvested fresh fish was 250.02 tons, the total output value reached 1.8247 million yuan, and the average output value per mu reached 11697.1 yuan; the total cost was 1.0003 million yuan, and the average cost per mu was 6411.9 yuan; the total profit was 824,400 yuan, and the average profit per mu was 5284.6. The input-output ratio was 1:1.82, achieving significant economic benefit.
IX. Summary and analysis
1. The high-yield and high-efficiency technology for two-season-per-year pond monoculture of grass carp mainly adopted technical measures such as stocking large-size fingerlings, increasing the stocking proportion of grass carp fingerlings and famous and superior varieties, reducing the stocking number of low-quality silver carp, feeding compounded pelleted feed for intensified culture, and ecological disease prevention, shortening the culture cycle, so that the stocked fingerlings could reach market size after 5 months of careful culture, effectively improving the unit yield and economic benefit of pond fish culture, and it is a good model for pond aquaculture.
2. After pond-cultured grass carp were injected with freeze-dried cell attenuated vaccine and “triple” vaccine, the immune effect was obvious, hemorrhagic disease had not yet appeared, the grass carp “three diseases” (rotten gills, red skin, enteritis) were significantly reduced, and the culture survival rate was greatly improved; the average survival rate of grass carp reached 95.4%, which was more than 25% higher than the survival rate of grass carp in ponds without vaccine injection. With the vaccine injection immunization prevention method, only 810 grass carp were stocked per mu of pond per year, requiring only a cost of 60 yuan, which was more economical and more effective than the method of using drugs for prevention and treatment. Using immunization to prevent grass carp diseases could reduce the residual amount of drugs used in fish, conformed to the standard requirements of pollution-free aquaculture, and was worth large-scale promotion and application.
3. In ponds mainly culturing grass carp, the feeding method of mainly feeding compounded feed, supplemented by green feed, and combining green feed with refined feed improved the conversion rate of compounded feed, reduced production costs, and shortened the adult fish culture cycle. In the mountainous areas of northern Fujian, before June there was abundant rainfall, and local resources of ryegrass planted in idle winter fields and wild green grass were abundant, so green feed could be mainly fed, supplemented by compounded pelleted feed; after June rainfall relatively decreased, the weather was hot, green grass was insufficient, and it was also the best period for fish growth, so compounded feed could be mainly fed, supplemented by part of green feed. The feeding method combining green feed and refined feed could not only reduce the labor intensity of fish culture, but also reasonably solve the contradiction between supply and demand of green feed, promote rapid growth of fish, and was conducive to developing from the traditional extensive culture type toward intensive, industrialized and large-scale aquaculture.
4. The high-yield and high-efficiency model of two-season-per-year pond monoculture of grass carp required a sufficient source of large-size fingerlings. Large-size fingerlings should be cultivated according to the proportion of 1 mu of fingerling pond for every 5 mu of adult fish pond, so as to ensure that the quantity of large-size fingerlings could meet production needs.