Analysis of High-Yield Grass Carp Farming Models and Supporting Technologies in Hunan Province
Teng's Aquaculture Business Network - Contemporary Aquaculture Magazine exclusive report:
Hunan Province is one of the main production areas for grass carp (Ctenopharynodonidellus) in China, with grass carp farming output reaching as high as 589,000 t (2013 statistics). The region has large water areas, and many are intensive culture waters, but the per-unit yield is generally low, with feed input per mu less than 1 t, and most per-mu yields below 1,000 kg. The majority of farmers operate at a scale of 10-20 mu, with per-mu profit of around 1,000 yuan. To better promote farming upgrading, increase per-unit-area yield and farming benefits, the following introduces supporting technologies related to promoting high-yield grass carp farming models in the Hunan market, based on market practice and scientific technology, with the aim of advancing Hunan's farming level and improving farmers' benefits.
1 Current Status of Grass Carp Farming in Hunan
In the Hunan region, polyculture of grass carp and crucian carp, combined with silver carp and bighead carp, is the main model, with grass carp having the highest output. However, because farmers do not carry out vaccine immunization for grass carp, the survival rate of grass carp is generally 50%-80%, and in extreme cases can be as low as 30%. During the farming period, insufficient attention is paid to the ecological balance of the water body, and ammonia nitrogen and nitrite often exceed standards, leading to difficulty in feeding and severe fish disease, resulting in low yield and farming profits that cannot be effectively guaranteed. Furthermore, most farmers plant large amounts of ryegrass, Sudan grass, and other forage grasses, mixing them with feed during the farming period. First, forage grass has high crude fiber content, which accelerates intestinal peristalsis, causing some feed to be excreted before being fully digested. Second, fish preferentially consume feed, causing some forage grass to rot in the water body, accelerating water quality deterioration.
After grass carp are grown out, it is already autumn and winter, which is the season when large quantities of grass carp are marketed. The concentrated marketing of grass carp leads to low grass carp prices, and farmers' enthusiasm for selling fish declines. In addition, competition from other regions (such as Guangzhou, etc.) drives prices even lower. As the year-end approaches, large quantities of grass carp remain in ponds, and with no other option, they can only be overwintered. Although grass carp prices improve somewhat after overwintering, it is only a drop in the bucket. Grass carp lose substantial weight during overwintering, and farmers' benefits are greatly damaged.
2 High-Yield Farming Model
A polyculture model of grass carp and crucian carp of different sizes, combined with silver carp and bighead carp (see Table 1). This model focuses on producing warm-water fish, increasing per-unit-area yield. From August to September, fish are sold 1-2 times per month, and per-mu yield is raised from 500-750 kg to 1,000-1,500 kg. Where conditions are mature, farmers can attempt to push for 2,000 kg.
Table 1 High-Yield Farming Model
3 Supporting Technologies and Conditions3.1 Disease Prevention and Control Technology
Grass carp vaccine injection technology (this technology is key to the success of small grass carp farming). Grass carp branchial necrosis disease, red skin disease, and enteritis disease lead to low survival rates of grass carp, while the grass carp triple vaccine, through intramuscular injection or intraperitoneal injection, improves the survival rate of grass carp and reduces disease risk, thereby improving benefits. Currently, grass carp vaccines mainly come from traditional methods. Through vaccine injection, the survival rate of grass carp can basically reach above 90%. In addition, during peak feeding seasons, regularly mix liver- and gallbladder-protecting drugs (such as Gandanshuling, multivitamins, Qishen Immuno Powder, etc.) into feed monthly, and control the condition factor (K) within 1.9-2.4 by adjusting the feeding rate.
Note: K = (W/L3) x 100, where W is body weight (g), L is body length (cm, from tip of snout to base of caudal fin)
3.2 Balanced Aeration Technology
Balanced aeration technology mainly uses microporous aerators in combination with paddlewheel aerators. During the day, oxygen produced by photosynthesis is sufficient for fish growth; paddlewheel aerators are turned on to break the water layers and make dissolved oxygen uniform throughout the water body. At night, there is no photosynthesis, and both algae and fish in the water consume oxygen, so oxygen must be drawn from the air. Bottom aeration is turned on to press air into the bottom of the water; as the air escapes from the bottom to the surface, oxygen in the air gradually dissolves into the water body to achieve aeration. For aeration in the feeding area, since most fish activity is concentrated in the feeding area, dissolved oxygen in the feeding area water is low at this time, which is unfavorable for feed utilization and fish growth. Microporous aeration discs are concentrated in the feeding area to avoid oxygen deficiency there and ensure dissolved oxygen in the feeding area remains above 4 mg/L.
3.3 Precise Feeding Technology
Precise feeding technology uses a 1:1 combination of extruded feed and medium-to-high-grade hard pellet feed, fed during high-temperature and low-temperature seasons (water temperature >30°C or<24℃）使用硬颗粒饲料；在适宜鱼体生长的温度（24℃≤水温≤30℃）采用高档饲料或膨化饲料；在高温季节，早晚投喂膨化饲料，在水温较高的中午投喂硬颗粒饲料，以减少摄食对鱼体的应激。
Separate-area feeding of grass carp and crucian carp. The method of feeding grass carp and crucian carp in separate areas is suitable for farming water areas of more than 30 mu with 2 or more feeders. During the farming period, larger grass carp are fed first, then smaller crucian carp. After about one week of conditioning, separate-platform feeding of grass carp and crucian carp can be formed. This method facilitates medication for grass carp, which are prone to disease.
Feeding principles at each stage of farming: from March to May, feed hard pellet feed; for grass carp, adjust the feeding rate according to condition factor (the higher the feed grade, the lower the feeding rate). From June to early July, feed extruded feed + hard pellet feed (hard pellet feed is fed at the normal feeding amount, while extruded feed is fed at 60%-80% of the hard pellet feed amount). From July to late August, feed hard pellet feed (extruded feed may be fed at breakfast and dinner), and pay attention to controlling the feeding amount. See Table 2 for the feeding rate when extruded feed is used throughout:
Table 2 Feeding Rate of Extruded Feed at Each Stage
3.4 Algae and Bacteria Regulation Technology
When grass carp are first stocked into ponds, the pond water is generally relatively clear and transparent. After a period of farming, the pond water deteriorates. At this time, in addition to removing debris from the pond, maintaining cleanliness and hygiene in the pond, and promptly removing dead and diseased fish, ecological regulation of water quality is needed.
At the end of April or the beginning of May each year, use disinfectant drugs such as "Duxiaojing" to disinfect the water body once. In May, use water-fertilizing and algae-culturing products such as "Feed Companion 2" once every 10-15 d to regulate water quality. From June to August, use algae-culturing products such as "Feed Companion 4" + bacteria-culturing products such as "photosynthetic bacteria" together once every 15 d or so to regulate water quality. Generally, use algae-culturing products first, then use bacteria-culturing products 1-2 d later to stabilize water quality. In September, use bacteria-culturing products such as "photosynthetic bacteria" + bottom-improving products such as "Gaishui Jiedu Bao" together once every 15 d to purify water quality. Generally, use bottom-improving products first, then use bacteria-culturing products 1-2 d later. When using water-conditioning products throughout the process, avoid using them together with sterilization and disinfection products. The use of these two types of products must be separated by 4-5 d. Generally, use sterilization and disinfection products first, then use bottom-improving and bacteria-culturing products.
4 Precautions for High-Yield Grass Carp Farming
Extruded feed is mainly used in models for selling warm-water fish (pursuing growth speed) and under high-density farming conditions, and is used to ensure the pond water environment. When using extruded feed, the feeder must be strictly controlled. For the feed usage model, it is recommended to use conventional hard pellet feed + extruded feed at a 1:1 ratio. If extruded feed is used throughout, it is necessary to prevent fatty liver and excessively high condition factor in grass carp. For ponds using compound feed, fish must be sold promptly after stopping feed (especially extruded feed), and overwintering is not recommended. If overwintering is necessary, a small amount of feed must be fed in winter to prevent weight loss during overwintering. Strictly carry out monthly sampling, focusing on recording the average fish weight and number of fish each month, promptly calculating the fish carrying capacity of the pond and adjusting the feeding rate.
1. Author | 1 Tongwei Co., Ltd. Fisheries Research Institute 2 Wuhan Tongwei Feed Co., Ltd. Zhang Dehong1 2 Liu Bo1
2. Source | Contemporary Aquaculture - Teng's Aquaculture Business Network
3. This article is an exclusive original manuscript of Contemporary Aquaculture - Teng's Aquaculture Business Network. Unauthorized reproduction is strictly prohibited!