Short-term fattening of wild caught shortfinned eels
Science Centres: Fisheries
During 2000-2001, NIWA undertook pilot trials to fatten shortfinned eels that were close to the commercial threshold size. The primary focus of the work was to minimise the costs of fattening eels by using existing pond systems and by identifying inexpensive and locally available foods. We investigated the reliable selection of females and their supplementary feeding as a means of increasing production from the wild fishery to improve supply for both commercial and Maori customary fisheries.
Results of fattening trials in farm ponds and in a pond of treated dairy wastes are encouraging. We found that females (which grow larger than males) can be reliably selected through grading of commercial, threshold-sized eels for ongrowing and that wild stocks in poor condition are not predisposed to poor growth. A proportion of these eels can be rapidly fattened in both farm ponds and treated dairy effluent, achieving up to 50 times their natural growth rate in Waikato waters.
Short-term, low level supplementary feeding of stocked farm ponds can achieve up to 14 times the production from source waters and result in stock of marketable condition. Even the short-term holding of eels in good quality farm ponds at lower than natural density without extra food can soon produce stock of marketable condition. Short-term rapid growth (220 g to 550 g in 2 months) and increase in condition can also be achieved in dairy factory wastewater without supplementary feeding. Individual growth rates were highly variable in both farm and wastewater ponds, and so a feed formulation that encourages rapid uniform feeding will be crucial to the success of any wild eel fattening enterprise.
We are monitoring a commercial company which is successfully fattening wild stocks on a more intensive scale using a “high tech” recirculating filtration system. Graded eels of 300 g mean weight grew to 800 g mean weight in just 50 days. NIWA has been investigating types of food that will initiate high levels of feeding in both eel species and can be readily adopted by both extensive and intensive fattening ventures.
This work was funded by the Foundation for Research, Science and Technology.
We pay tribute to our dear friend and colleague Lee Perry (Ngati Kahungunu, Te Kuwaha NIWA), tragically killed in September 2001, who was applying the findings of this work in intensive culture.