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

This study aimed to determine excretion rates of ammonia and urea of Australian short-finned Ž . elvers as influenced by varying dietary crude protein intake. Elvers 2.3"0.02 g were fed diets Ž . Ž . Ž . Ž . containing dietary crude protein levels of 25% P25 , 35% P35 , 45% P45 and 55% P55 dry Ž matter equivalent to 14.17, 19.24, 20.57 and 26.39 g CPrMJ, respectively pairs of diets P25, P35 . and P45, P55 were isoenergetic . Elvers were fed twice a day to a total of 6% BWrday and Ž . nitrogenous excretory products ammoniaand urea-nitrogen measured during the following 24 h and peak excretion rates occurred 4–8 h following both the morning and afternoon feed. Daily Ž . ammonia-nitrogen excretion was significantly P-0.05 higher on the P55 diet compared to the Ž P35 and P45 diets. Increasing dietary protein intake resulted in increasing ammoniays0.022 x 2 . Ž 2 q0.058; ns12; r s0.88; P-0.001 and urea-nitrogen ys0.0044 xq0.426; ns12; r s . 0.55; P-0.01 excretion. The highest urea-nitrogen excretion as a percentage of consumed Ž . nitrogen was measured for fish fed the P25 diet 41.99"2.62% and compared with 30.29 Ž . Ž . Ž . "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 ureanitrogen excretion indicates that urea is an important excretory end-product in this species. q 2001 Elsevier Science B.V. All rights reserved.