Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels

Juvenile (12-152 g) shortfinned eels Anguilla australis and longfinned eels A. dieffenbachii caught in New Zealand streams were fed squid mantle Notot odarus spp. 4 days per week in laboratory experiments. A linear multiple re gression equation showed the amount of food eaten (0-2.7% w day(-1)) explai ned 77.7% of the variation in specific growth rates (- 0.60 to + 1.07% w da y(-1)) among individual eels, while previous growth rates, water temperatur e (10.0-20.6 degrees C), and eel weight (12-152 g) explained a further 5.6, 1.4 and 0.8%, respectively. Growth in length ranged from - 0.3 to + 0.9 mm day(-1). Eels which were starved and then given high rations grew substant ially faster than expected. Once growth rates were adjusted For differences in ration and other factors, there were no significant differences in grow th rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water tem peratures and ceased below 9.0 degrees C. Growth rates in the wild were sub stantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild. (C) 2000 The Fisheries Society of the British Isles.