Detailed Explanation of Small-Volume High-Density Cage Fish Farming Technology
Small-Volume High-Density Cage Fish Farming Technology
I. Introduction and Promotion of Small Cage Fish Farming Technology
Small cage fish farming technology, namely small-volume high-density cage fish farming technology, was introduced to China from the United States in 1991. In the summer of 1994, Dr. Smith, an aquaculture expert from Auburn University in the United States, came to our province and held the first training course on small cage fish farming technology. Since then, this technology has been gradually promoted in our province. Huangshan, Anqing, Ma'anshan, Hefei, Bengbu, Huainan, Lu'an and other cities and prefectures all have a certain scale of farming. According to incomplete statistics, in 1999 the province's promoted farming area reached 15,000 cubic meters.
II. Characteristics and Advantages of Small Cage Fish Farming
The main differences between small cage fish farming and traditional cage fish farming are:
First, the volume is small. Traditional cages generally have an area of several dozen square meters and a depth of about 2 m, with a volume of several dozen to one or two hundred cubic meters, while small cages are usually 1-4 cubic meters.
Second, small cages have a high stocking density of fingerlings and a high yield per unit area.
Third, small cage fish farming relies entirely on artificial feeding of complete formula feed, and high-quality varieties in demand can be selected for farming according to market demand.
Small cage fish farming has many advantages in production:
First, because of its small volume, it is suitable for installation in many kinds of waters. It can be installed in reservoirs, lakes and rivers, and can also be placed in larger and deeper ponds.
Second, because small cages have high yield per unit area, installing them in large water bodies and combining intensive small cage farming with large water body enhancement can rapidly increase the total output and yield per unit area of medium and large waters.
Third, small cages are easy to make, simple to operate in production, and the farming technology is easy for the public to master, making them very suitable for household operation.
III. Materials, Manufacturing Methods and Installation of Small Cages
1. Materials required for the cages. These mainly include polyethylene netting, steel bar frames, moso bamboo, iron wire, netting twine, shading cloth, feed pipes, etc. Polyethylene netting is the main material for making small cages. The commonly selected netting twine specification is 3×3-3×4, with a mesh size of 2-3 cm, single layer. In addition, a layer of fine-mesh net must be laid on the bottom of the cage to prevent feed loss. The steel bar diameter is 0.8-1 cm, and according to the required size of the cage body it is welded into a cube or rectangular frame. Its function is to keep the cage stretched open as a whole, and at the same time it can prevent the cage from floating up, so that the cage maintains maximum volume. Moso bamboo with a diameter of 8-10 cm is cut to length according to the size of the cage area, tied into a square frame, and fastened to the upper opening of the cage. Because moso bamboo is hollow and has great buoyancy, it mainly serves as a float. In addition, the feed pipe is usually also made of moso bamboo, with a length comparable to the depth of the cage, but the bamboo nodes in the middle must be knocked through. Iron wire and netting twine serve to reinforce. For the shading cover cloth, ordinary rainproof cloth can be selected; it is required to be black and durable. Its area is comparable to the cage area.
2. Manufacturing of the cage. First weld the steel bar frame, then stretch the netting tightly and fix it outside the frame to form a fully enclosed hexahedral cage. Add another layer of fine-mesh net on the cage bottom, with the surrounding part 10 cm higher than the cage bottom. Add a moso bamboo frame to the upper opening of the cage, set a feed pipe vertically in the exact center of the cage, with the lower opening of the pipe 10-15 cm from the cage bottom, and then add a shading cloth cover.
3. Installation of small cages. Good water quality and an open area are required, and medium and large reservoirs with a certain slight water flow are the most ideal waters. The cage farming area must avoid navigation channels, flood discharge gates, and water inlets where mountain torrents may rush in during summer. Small cages should be arranged in a straight line, with the direction perpendicular to the slight flow direction in the water body, to facilitate water exchange inside the cages. The spacing between each row should be no less than 20 m, and the spacing between each cage should be more than 2 m. Cages are connected to one another with iron wire or steel cable, and the two ends are fixed on the shore or sunk in the water with iron anchors or large stones.
IV. Species, Size, Density and Stocking Time for Small Cage Farming
1. Farming species. At present, the species that can be farmed in small cages mainly include common carp, tilapia, channel catfish, crucian carp, blunt snout bream, grass carp, etc. Each locality can flexibly choose suitable species for farming according to local market demand, the difficulty of obtaining fry and fingerlings, and other factors.
2. Size. Small fingerling size is not conducive to feed preparation and feeding, and also affects the marketing of commercial fish. Therefore, fingerlings are generally required to be 50-75 g each. Crucian carp and blunt snout bream may be smaller, but should not be less than 30 g each.
3. Stocking density. The suitable yield per unit area for small cage farming of common carp, tilapia, etc. is about 150-200 kg per cubic meter, and 80-100 kg for crucian carp. The stocking density of fingerlings per cubic meter is preferably 300-400 fish. Fingerlings must be uniform in size.
4. Fingerling stocking time. Common carp, crucian carp, blunt snout bream, etc. can generally be stocked when the water temperature stabilizes at 12-15°C, while tropical species such as tilapia are best stocked when the water temperature stabilizes at 20°C. It is worth noting that about 10 days before the fingerlings are put into the cage, the cage should be placed in the water so that some algae grow on the netting and form a biofilm, which can reduce abrasions on the fish body and avoid disease.
The fingerlings should be robust in constitution. At stocking, they must also be bathed and disinfected for 10-15 minutes in 3%-4% salt water or 8-10 mg/L malachite green solution, etc., to prevent fish disease.
V. Feed and Feeding
1. Feed. It is required to be comprehensive and reasonable in nutrition. The protein content is generally 28%-32% for tilapia feed, 30-36% for common carp feed, and 28%-30% for grass carp feed, and the amino acids must be balanced. The particle size of the feed must match the size of the fish. For example, for a body weight of 50-75 g, the particle size is 2 mm; for a body weight of 75-150 g, the particle size is 3-4 mm; for a body weight above 150 g, the particle size is 4-5 mm. The feed must have a certain stability in water, and is required not to disintegrate within 10 minutes.
2. Feeding requirements. Feeding can begin on the second day after the fingerlings are put into the cage. The amount of feed used must be determined according to fish body size, water temperature, and so on. When the water temperature is below 20°C and the fish body weight is between 50-500 g, the daily feeding amount is 2.5%-1%; at 21-25°C, the daily feeding amount is 3.5%-1.5%; at 25-30°C, the daily feeding amount is 5%-2%. As the fish grow larger, sampling should be done every 10-15 days to analyze the growth situation and adjust the feed amount. Feed should be put centrally into the feed pipe. When the water temperature is relatively low, feed 1-2 times a day, at 8-9 a.m. and 2-3 p.m. When the water temperature is relatively high, feed 3-4 times a day, at 8-9 a.m., 11-12 a.m., 2-3 p.m., and 5-6 p.m.
VI. Daily Management
Dedicated personnel are required for management. Generally, one person can manage 20-25 small cages of 1 cubic meter, or 15-20 cages of 2-4 cubic meters.
Observe the feeding and activity of the fish every day, regularly check the growth situation, and when cessation of feeding, dead fish, or abnormal growth are found, promptly identify the causes and take improvement measures.
Safety awareness must be strengthened, and the "four preventions" must be effectively carried out, namely preventing flood impact, preventing fish escape due to net breakage, preventing theft, and preventing disease.
Keep production records at ordinary times, recording in detail the original data such as the time, quantity, weight, size, feed amount, weather changes, and the types and amounts of drugs used for disinfection, disease prevention and treatment for each cage of stocked fingerlings, as well as the final yield and size, so as to facilitate summarizing experience and conducting cost accounting at the end of production.