Growing and harvesting eels
Shortfin and longfin eel aquaculture
Glass eels and elvers are best stocked into tanks before being moved into growout facilities. Growout of elvers to market size can be achieved in either tank systems or earthen ponds. Tank culture can be managed in tanks of 1000-20,000L, with flow through or recirculating water supply. Recirculation requires sophisticated biofiltration treatment technologies to maintain suitable water quality.
Earthen ponds for eel growout should be constructed on non-porous soils. Sandy clay soils are optimal to prevent pond leakage. It is possible to line ponds so that they do not leak, however construction costs will be higher. Ponds range in size from 0.2-2ha and are 1-1.5m deep.
Eels should be quickly weaned onto artificial feed from the time they enter the farm. A range of commercial fish diets (pellets) is available in Australia, which are suitable for shortfin and longfin eels. Eels are fed several times a day, which ensures they are healthy and grow rapidly.
Food conversion ratios (FCR) for both shortfin and longfin eels should be in the range of 1.5-2:1 (kilogram of food: weight growth).
Eels are harvested at a weight varying from 150g to several kilograms, depending on the market. Harvesting can be carried out by draining the pond using a net attached to the outlet pipe, a seine net or a scoop net (at feeding time).
The eels are then sorted into different sizes using a grading tray, and placed in holding tanks for several days without feed to purge their stomachs. They are then chilled and packed into strong plastic bags with just enough water to ensure that their skin remains moist. The bags are then filled with oxygen and transported to the market.