Raising eels without mud and changing water

Master Le Ngoc Hanh researched the technology of raising eels without mud in a circulating tank without changing the water, shortening the raising time by up to 2 months.

In 2011, Master Hanh, Aquaculture Research Institute 2 participated in a project to raise pangasius using recirculation technology sponsored by Wageningen University (Netherlands). During the 3 years of implementation, he thought about applying the recirculation principle to other aquatic species such as eels, crabs, etc. In 2014, he built a process to raise eels without mud using a closed recirculation system, using a water treatment system to create the best environment for eels to grow quickly.

The system includes a breeding tank of about ^4m2 (2m diameter), designed in a square shape with rounded edges to ensure effective water circulation across the entire surface and maximum breeding area. The breeding tank also has substrates such as nets, plastic fibers. for the eels to have a place to hide and come up to breathe on the water surface.

The water treatment system includes mechanical filtration and biological filtration to remove waste and excess food in the water. Toxic gases dissolved in the water are biologically treated with media. The circulation system has additional equipment, oxygen supply, UV sterilization and sand decolorization equipment to help the water have a clearer color.

Eels grow after one month using mud-free farming technology using a recirculating system at the experimental farm of the Tien Giang Agricultural Extension and Services Center. (Video: NVCC)

According to Master Hanh, traditional eel farming requires changing the water 1-2 times per day. Recirculating eel farming does not require this throughout the farming process. Farmers only need to add a small amount of water to compensate for evaporation or pipeline leaks. This helps farmers save a large amount of water each crop, reducing labor.

In addition, the circulation system will help the eel's living environment stay clean and more stable than the water-changing farming method. The reason is that changing the water will disrupt the eel's living environment, affecting their growth ability. "Water-changing farming can take 10-15 months to harvest. The circulation technology only takes 8-10 months ," said Mr. Hanh. In addition, farmers currently raise eels mainly using well water, which may contain some toxic residues that, if not treated, will affect the growth rate of the eels.

Operational diagram of the 8-tank model. (Photo: NVCC)

Because it uses a filtration system, oxygen supply, and sterilization, the recirculation technology will consume about 3 times more electricity than eel farming with water replacement. However, according to Master Hanh, this technology allows for a maximum density increase of 5 times on the same area and shortens the time, so it can offset the cost of electricity.

The tank is typically designed to be about 2 m in diameter with an area of ​​about 4 m2. Each tank can hold 2,000 fry (about 500 per m2), yielding 400 - 500 kg of eel meat and can increase the density to increase productivity.

Eel farming profits are estimated at 20%, meaning the investment for each kilogram of eel is about 100,000 VND, the average selling price is about 120,000 VND. The investment cost for recirculating farming equipment for a 5-ton scale is about 400 million VND. At this scale, farmers earn about 100 million VND per crop. Thus, raising 3-4 crops will recover the capital if not counting the cost of the breed. "This is not a quick way to get rich, but this technology is sustainable, suitable for urban agriculture with limited space and water resources ," said Mr. Hanh.

Mechanical filter equipment of the system. (Photo: NVCC)

In March 2021, the mud-free eel farming model in a recirculating tank was tested at the Tien Giang Agricultural Extension and Agricultural Services Center, with a scale of 4 farming tanks with an area of ​​about 4.8m2 ^each . The model was tested with different densities for evaluation, with an average yield of 50kg of eel per ^m2 .

According to Mr. Nguyen Tan Quoc, Director of the Center, the experimental farming process was initially effective when there was no need to change the water but the eels still developed well and grew rapidly in the first month. "With this model, the investment cost is not too large but it can create livelihoods for people who do not have large land conditions or areas with scarce clean water can also be implemented ," said Mr. Quoc.