Ammonia and urea excretion rates of juvenile Australian short-finned eel (Anguilla australis australis) as influenced by dietary protein level

K. Engin, C.G. Carter-2001

Aquaculture, 194 (1-2): 123-136

Abstract:

This study aimed to determine excretion rates of ammonia and urea of Australian short-finned elvers as influenced by varying dietary crude protein intake. Elvers (2.3±0.02 g) were fed diets containing dietary crude protein levels of 25% (P25), 35% (P35), 45% (P45) and 55% (P55) dry matter equivalent to 14.17, 19.24, 20.57 and 26.39 g CP/MJ, respectively (pairs of diets P25, P35 and P45, P55 were isoenergetic). Elvers were fed twice a day to a total of 6% BW/day and nitrogenous excretory products (ammonia- and urea-nitrogen) measured during the following 24 h and peak excretion rates occurred 4--8 h following both the morning and afternoon feed. Daily ammonia-nitrogen excretion was significantly (P<0.05) higher on the P55 diet compared to the P35 and P45 diets. Increasing dietary protein intake resulted in increasing ammonia- (y=0.022x+0.058; n=12; r²=0.88; P<0.001) and urea-nitrogen (y=0.0044x+0.426; n=12; r²=0.55; P<0.01) excretion. The highest urea-nitrogen excretion as a percentage of consumed nitrogen was measured for fish fed the P25 diet (41.99±2.62%) and compared with 30.29 (±3.58%), 25.76 (±1.41%) and 23.57 (±1.54%) for diets P35, P45 and P55, respectively. The Australian short-finned eel appeared to be similar to other teleost and eel species in terms of the magnitude of ammonia-nitrogen excretion following feeding. However, higher rates of urea-nitrogen excretion indicates that urea is an important excretory end-product in this species.

(School of Aquaculture and Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Locked Bag 1-370, Launceston, Tasmania 7250, Australia)

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