Southern Catfish Silurus Meridionalis, Starvation Nitrogen Excretion And Energy Use

A starvation experiment was conducted on 120 juveniles of the southern catfish(Silurus merldionalis) with initial weight of 33.27?.13g at 27.50 from May 24 to August24, 2000. The experiment ended at the 92th day when half of the tested fishes were dead.Ammonia-N excretion rate and routine metabolic rate of 18 fishes were measured, and asampling of body composition was made every 4 days during starvation. The results were following:(1)Ammonia-N excretion rate increased at the beginning period and then decreased slowly in the following starvation days. From the 1St day to the 12th day, the excretion rate increased from 5.59mg-N/(kg.h) to 8.34mg-N/(kg.h); from the 12th day to the 28th day the rate changed little, and the average rate was 8.35 ?0.1 9mg-N/(kg . h), ranging from 8.20 mg-NI(kg.h) to 8.34mg-N/(kg.h); after the 28th day the rate decreased slowly, reaching 6.93 mg-N/(kg. h) at the death of fish. During starvation total nitrogen lose rate in the fish body was 0.24?.01g-N/(kg.d)~ and average ammonia nitrogen lose rate was 0.19?.Olg-N/(kg.d) which accounted for 69.67?1.8% of the former one. And the total energy expenditure rate was 41.65? .43KJ/(kg . d), the ammonia-N s energy lose rate was 4.72監.25KJ/(kg. d) which accounted for 11.34?.58% of the former one.(2)The ratio of excretion-N to body protein-N increased significantly during starvation, from 0.5 9% at the beginning of starvation to 1.13% at the death of fish. The relationship between ratio of excretion-N to body protein-N (y) and starvation time (t) can be described as: y =0.450 + 0.147Ln(t) (n18, R2 = 0.898, p