High-yield aquaculture management techniques for intensive grass carp pond culture
Grass carp grow rapidly, with the fastest increase in body length occurring at 1 to 2 years of age, while the fastest weight gain occurs at 2 to 3 years of age. Once the fish reach sexual maturity at 4 years of age, growth slows down significantly. Under natural conditions, a 1-winter-old fish has a body length of about 340 mm and a body weight of about 750 g; a 2-winter-old fish has a body length of about 600 mm and a body weight of 3.5 kg; a 3-winter-old fish has a body length of about 680 mm and a body weight of about 5 kg; a 4-winter-old fish has a body length of about 740 mm and a body weight of about 7 kg; a 5-winter-old fish can reach a body length of about 780 mm and a body weight of about 7.5 kg; and the largest individuals can reach about 35 kg.
Aquaculture conditions
1. Pond conditions: area of 5 to 10 mu, flat pond bottom, loam substrate, 10 to 20 cm of bottom mud, and a water depth of about 2 m. Ponds should be oriented east-west, and each pond should be equipped with one 3 kW impeller-type aerator and one 4-inch water pump.
2. Clearing and disinfection: Under dry pond conditions (with 5 to 10 cm of standing water), apply 100 kg of quicklime per mu after slaking it into a slurry and splash it over the entire pond, or apply 10 kg of bleaching powder per mu, dissolve it in warm water, and splash it over the entire pond, making sure no dead corners or untreated surfaces are left, so as to thoroughly kill pathogenic bacteria.
3. Water quality: pH 7.5 to 8.5; during the peak culture season (June to September), pond water transparency should be maintained at about 30 cm, and the organic matter oxygen demand (COD) should be 18 to 20 mg/L.
4. Fingerling selection: Grass carp fingerlings should be selected with a golden-yellow body color, no external injuries, lively and robust, and a body weight of about 100 g per fish. At the same time, because both grass carp hemorrhage and enteritis are highly susceptible to infecting fingerlings of the current year, it is best to choose 2-year-old fingerlings when selecting seedlings.
5. Fingerling stocking
a. Stocking time: Two methods are used, spring stocking and autumn stocking. Spring stocking is carried out when the water temperature rises back above 12°C, and autumn stocking is carried out when the water temperature is between 15 and 12°C.
b. Stocking mode: Stocking modes are divided into main culture and polyculture, with main culture as the primary mode. In the main culture mode, grass carp account for 80% to 85%, with 20% to 15% silver carp, bighead carp, bream, and crucian carp added.
c. Stocking size and density: When grass carp are stocked at a total length of 15 to 20 cm, the stocking density should preferably be 1400 to 1600 fish per mu. When grass carp are stocked at a total length of 20 to 25 cm, the stocking density should preferably be 1200 to 1400 fish per mu.
5. Fingerling disinfection: Before stocking, soak the fingerlings in 3% to 4% salt water, or 20 mg/L potassium permanganate, or 20 to 30 mg/L povidone-iodine (containing 1% available iodine) for 5 to 10 minutes.
6. Fish feed: The feed used for intensive grass carp pond culture is mainly compound feed, accounting for 85%, supplemented by green fodder, accounting for 15%.
7. Feeding management: Feeding in intensive ponds is the main work during the feeding management stage, including routine feed feeding and medicated bait feeding. The feeding method uses artificial training for feeding at fixed points, and strictly adheres to feeding with fixed quality, fixed quantity, fixed time, and fixed location. The specific practices are as follows:
a. Routine feed feeding: Feed is mainly pelleted feed, with a protein content of 28% to 32%, supplemented by green fodder. Feed feeding follows the principle of "coarse first, fine later." As for feeding frequency, from mid-March to May, feed 2 to 4 times daily; from June to mid-August, feed 3 times daily; from mid-August to October, feed 4 times daily. Starting in June, feed green fodder once daily, and the amount fed should not be too large; it is best to feed until 80% full, and strictly avoid overfeeding or underfeeding. Generally, the daily feeding amount should be controlled at about 3% to 5% of the body weight of the feeding fish, divided into two feedings in the morning and afternoon. The morning feeding should account for about 20% of the daily feeding amount, and the afternoon feeding should account for about 80%.
From March to June, mainly feed pelleted feed with a protein content of 28%, with a daily feeding rate of 3%, and feed an appropriate amount of green fodder.
From July to September, control the amount of pelleted feed, with a daily feeding rate of about 1.5%; the pelleted feed protein content is 28%; increase the amount of green fodder fed to control the occurrence of fish diseases.
From October to November, feed pelleted feed with a protein content of 32%.
After continuous feeding of pelleted feed for a period, pelleted feed should be stopped for 1 week, and during the interval, raw grain feed should be fed. At ordinary times, pay attention to appropriately adding vitamins and other drugs to the feed to avoid diseases such as hepatobiliary syndrome in grass carp that can cause massive mortality.
b. Feeding precautions: Feeding should follow the "three looks."
Look at the season: Water temperature differs across the four seasons, so start feeding early and stop feeding late, and in between let the fish eat their fill and eat well to promote growth;
Look at the weather: When the weather is clear and dissolved oxygen in the water is high, the fish feed vigorously, so feed appropriately more; when the weather is muggy and dissolved oxygen in the water is low, the fish have poor appetite, so feed less or not at all, and feeding can also be stopped during strong wind and heavy rain;
Look at the water color: Water color is a comprehensive phenomenon of water quality. When the water quality is clear, the water color is normal, the fish feed vigorously, and normal feeding can be carried out; when the water color is too dense and the fish gasp at the surface, feed less or stop feeding.
c. Key points of feed feeding
Storage time should not be too long: Pelleted feed contains 12% to 14% moisture during processing. If stored too long, it easily absorbs moisture and becomes moldy, affecting the use value of the pelleted feed, and after feeding, fish are prone to disease. Therefore, storage time should not be too long.
Increase feeding frequency: Fish have no stomach, and feed stays in the intestine for a short time. Therefore, while keeping the total feeding amount unchanged, the number of feedings should be increased and the amount per feeding reduced, so that the fish remain in a semi-hungry state, which can improve feed utilization and reduce the feed conversion ratio.
There should be a certain feeding area and time: In polyculture ponds with multiple species, crucian carp and grass carp compete quickly for food and eat a large amount, while bream eat "politely" and correspondingly eat less, which often affects their growth. Therefore, before using pelleted feed, short-term training should be carried out so that the fish develop the feeding habit of a fixed feeding ground and fixed time. Each feeding should be spread evenly, the feeding time should be no less than 30 minutes, and the feeding area should be 40 to 60 sq m, so that every fish can take in feed.
Particle size should be reasonable: When fingerlings are stocked, the water temperature is low, growth is slow, and the size is small, so a pelleted feed particle size of 2 mm is more suitable. As the temperature rises and the fingerlings grow, the feed particle size during the mid-culture period is 3 to 3.5 mm, and during the late culture period it is 4 to 4.5 mm.
Add salt and allicin to prevent fish diseases: When making pelleted feed, mix appropriate amounts of salt and allicin evenly into the raw materials, which can disinfect and sterilize and prevent fish diseases.
b. Medicated bait feeding: Sulfaguanidine is used as the medication, made into floating feed. The method is as follows:
Mix 1 jin of wheat bran with every 5 g of sulfaguanidine, then add 3 liang of elm bark powder or sweet potato powder, blend with hot water, press into small pieces, and sun-dry for later use.
Feeding method: Mix the medicated bait into the pellets. On the 1st day, use 1 g of medication per 20 jin of pond fish body weight; from the 2nd to the 6th day, halve the daily dosage for feeding. Feed once daily, with 6 days as one cycle, and feed one cycle every 1 to 1.5 months.