Development of an outdoor super-intensive recirculation eel culture system.

Abstract

A Danish type indoor super-intensive recirculation system was built outdoors and modified in order to significantly reduce the cost of the system, especially the cost of the greenhouse . A sun net sheltered the whole system. Submerged biofilter, trickling biofilter, and drumfilter were installed the same as in the indoor system . However, modified paddlewheel aerators replaced the oxygenation equipment. Illumination, chiller and UV sterilization equipment were removed. A rearing experiment of the European eel Anguilla anguilla was carried out from Jan. 6 to Oct. 6, 1999. In the system, 430 .71 kg and 864.49 kg of eels of average weight 128 g per eel was stocked in two 5 m xS m xl .8 m ponds, respectively. At harvest on October 6, 1999, a total of 2,899.23 kg was recovered. The total weight increment was 1,604.03 kg, which is 13 times more than the production of a conventional outdoor system in the same area. The water usage was 1.34 metric ton per kg of eel produced, higher than the indoor system (0.7 metric tons/kg), but far less than the conventional outdoor eel ponds (20-30 metric tons/kg) . Daily recording of water temperature, air temperature , DO, pH, transparency, death rate and feeding rate was carried out. A computer based water quality monitoring system was used to record continuously water and air temperature, and DO. It was found that the environment was no less stable than the indoor system. With similar biofilter capacity, the NH4 · level was kept at very low level. The performance of the system in terms of eel production was as good as the indoor system, while the capital cost of the outdoor system is about two-thirds that of the indoor system.