Estimation of the starvation losses of nitrogen and energy in the rainbow trout (Oncorhynchus mykiss) with special regard to protein and energy maintenance requirements

Literature data are analysed regarding losses of body substances occurring during a period of food deprivation in rainbow trout (Oncorhynchus mykiss). Nitrogen (protein) and energy losses show a distinct dependence on fish mass (FM [g]) and water temperature (T [degrees C]). Several regression models for this relationship were compared with best testing estimates as follows: Nitrogen loss [mg N 2 fish(-1) 2 d(-1)] = 0.0658 e((1.037)) 2 FM(0.739) (n=49, 9-20 degrees C, 5-400 g fish mass, P < 0.001, B=0.826) Nitrogen-corrected energy loss [J 2 fish(-1) 2 d(-1)]=22.09 e((1.034)) 2 FM(0.833) (n=63, 9-25 degrees C, 8-400 g fish mass, P < 0.001, B=0.887). For nitrogen loss as well as for nitrogen-corrected energy loss, the metabolic rate shows a progressive increase with rising water temperature. The temperature coefficient increases in magnitude as temperature increases. The introduction of a general common exponent (0.8 instead of 0.739 for nitrogen loss and 0.833 for energy loss) for fish mass decreases the precision of the estimate. The equations could serve as a base for estimating net protein and net energy maintenance requirements of rainbow trout. Possible limitations, caused by uncertainities in estimating the elevated metabolic rate by food intake and ingestion, are discussed.