First, water area selection and cage setup
When choosing a water area for raising fish in cages, it's important to select a location with clean, unpolluted fresh water. The site should have a wide surface area, stable water levels, and good water clarity—ideally over 60 cm. Dissolved oxygen levels should be at least 5 mg/L, and the depth should be more than 3 meters. It's also beneficial if the area is sheltered from direct sunlight and has small, naturally flowing bays, coves, or reservoirs that provide gentle currents.
The cages should be made of a single-layer polyethylene mesh with mesh sizes smaller than 1.5 cm. Cage sizes typically range from 1 to 28 m², but optimal sizes are around 451.8 m², 441.8 m², and 431.8 m². These cages should be open-top to allow for easy access and water exchange. The frame can be constructed using bamboo as both a float and support structure, while a 6.5 mm diameter wire mesh is used as the bottom frame and sinker. To stabilize the cage, stones can be placed in the corners. The top of the net should extend at least 20 cm above the water level.
Cages are usually arranged in a "one" shape, with one main cage for eels and two bait fish cages placed alongside. They are lined up in a row, with each cage spaced 5 meters apart and positioned perpendicular to the direction of the current. This layout helps maintain good water circulation within the cages.
Second, fish species stocking
It's best to use healthy, disease-free fish with uniform size. The individual size should be over 3 cm, ideally between 50–100 grams per fish. To avoid aggression among fish, larger fish should be stocked during winter. Stocking density is generally between 10 to 35 fish per square meter. Before placing the fish into the cage, each square meter of water should be treated with 0.1 ml of formalin or 10 grams of potassium permanganate solution for 10–15 minutes to eliminate parasites and bacteria on the fish.
For bait fish, low-value species such as whitefish, squid, tilapia, and small scavenger fish are preferred. These are usually raised during summer. Stocking density for bait fish ranges from 6,000 to 8,000 per square meter, and new feed is added as needed. Feeding should be done in the early morning or late evening, and live fish is ideal as bait. The feeding amount is about 20 times the weight of the carp. The bait size should be about half the length of the carp. The ideal water temperature for feeding is 25°C or higher. Feeding frequency varies: every 1–3 days when the temperature is between 20–25°C, once every 7 days at 15–20°C, and once every 20 days when the temperature drops below 10°C.
Third, management of the net cage
Eel farming in freshwater generally has fewer diseases, but they can still be affected by trichomonads, slugs, rickets, and gill rot. To prevent this, water plants like water hyacinth or water lettuce can be placed inside and around the cages to provide habitat for the eels. During hot seasons, strong chlorine solutions or insecticides can be used around the cages to control pests. If an illness occurs, medicated baths can be applied by suspending the four corners of the cage. It's recommended to clean the cages every 10–15 days. Additionally, it’s important to monitor wind and wave conditions and manage breeding activities based on the fish's growth to ensure their survival and health.
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