Detailed Explanation of Small Cage Culture Techniques for Tilapia
Small cage culture refers to high-density fish farming in small cages with a volume of 1-4 cubic meters. Because tilapia tolerates low dissolved oxygen and has strong disease resistance, it is relatively suitable for high-density cage culture.
1. Selection of culture conditions: Choose small cages in sheltered and sunny spots with broad water surface, stable water surface, no strong winds and waves, and a year-round water depth maintained above 5 m, with clear and pollution-free water quality, in reservoir branches, branch canals and other places; it is best to have a certain amount of slight flowing water, and the water flow speed is preferably 3-10 m per minute.
2. Fabrication and installation of small cages. The small cage is mainly composed of a frame, cage body, cage cover, feeding pipe, feeding tray and other parts. The upper frame is made of bamboo or wood, and the lower frame can be made of 4-6 mm round steel; the cage body is sewn from 2×2 polyethylene netting, and the mesh size of the netting is determined according to the size of the fingerlings stocked, generally 2-3 cm; the cage cover is made of opaque photosynthetic fiber woven cloth, with length and width 10 cm longer than the upper frame for sewing; the feeding pipe is made of plastic pipe with a diameter of 7-10 cm or moso bamboo with the nodes knocked through, installed at the exact center of the upper part of the cage, with the upper end 20 cm above the cage body and the lower end extending to 10 cm from the cage bottom; the feeding tray is made of polyethylene netting with a mesh size of 1-2 mm, with length and width each 15 cm longer than the lower frame, and used as a border frame. The small cages are arranged in the water in a straight line or a tripod shape, and the distance between cages is kept above 5 m. The cage bodies are connected with polyethylene ropes, then sunk into the water with stones, with the cage body more than 0.5 m above the water bottom, and fixed by driving stakes on the shore. The small cages are put into the water about 7 days before the fingerlings are stocked, so that the netting first becomes attached with some organisms and becomes smoother, to prevent injury to the fish body from abrasion.
3. Fingerling stocking. When the water temperature is stable above 18°C, stocking can begin; aim to stock early to extend the growth period and improve the size and yield of marketable fish. Generally, stock 400-500 tilapia with an individual weight of 50-100 g per square meter, or 300 tilapia with an individual weight of 100-150 g per square meter. The stocked fingerlings must be robust and relatively uniform in size. To prevent infection with fish diseases caused by handling injuries, the fingerlings must be disinfected before entering the cage. The disinfection method can be soaking the fingerlings in about 3% salt water for 5 minutes or bathing them in a 15 ppm bleaching powder aqueous solution for about 20 minutes.
4. Feeding management
(1) Feeding techniques: Small cage fish farming must use complete formula pellet feed. The feed can be self-mixed or purchased as finished special feed. The feed is required to remain stable in water for at least 10 minutes, and the storage period of the feed must not exceed one month. Fingerlings generally adapt to life 1-2 days after entering the cage, and feeding training can then begin. During the training period, feed at a daily feeding rate of 0.5%, keeping the fish in a semi-starved state so as to quickly form a conditioned reflex of rising to compete for food. After feeding training is completed, begin feeding the feed. When the water temperature is lower, tilapia eats less, and they can be fed 2-4 times per day. When the water temperature is higher, which is also the period of vigorous fish growth, they need to be fed 5-6 times per day. The daily feeding amount for each cage can be calculated according to the following formula: feeding amount = feeding rate × total fish weight in the cage.
The feeding amount is adjusted about once every 7 days, and the total weight of fish in the cage is sampled and investigated each month. Because tilapia is highly voracious, each daily feeding time should be controlled to 20-30 minutes, ending when 80%-90% of the fish are full and leave. When feeding, pour the feed into the feeding pipe at one time.
(2) Daily management: Persist in inspecting the cages every day, checking whether the cages are damaged, and preventing escape or theft; especially carefully inspect the netting about 30 cm from the water surface. Remove weeds and dirt on the cages, scrub the cages, keep the cages clean and water exchange unobstructed, observe the fish activity and growth so as to adjust the feeding rate in time, and at the same time pay attention to checking for diseases.
5. Harvesting
Stop feeding the feed 2-3 days before harvesting. During harvesting, first lift the bottom net at one end of the cage, insert a bamboo pole under the bottom net, drive the fish to the other end of the cage, and scoop them out with a dip net.