| Summary: | We evaluated measures of bioelectrical impedance analysis(BIA) and Fulton’s condition factor (K) as potential nonlethal indices for detecting short-term changes innutritional condition of postsmolt Atlantic salmon (Salmo salar). Fish reared in the laboratory for 27 days were fed, fasted, or fasted and then refed. Growth rates and proximatebody composition (protein, fat, water) were measured in each fish to evaluate nutritional status and condition.Growth rates of fish responded rapidly to the absence or reintroduction of food, whereas body composition (% wet weight) remained relatively stable owing to isometric growth in fed fish and little loss of body constituentsin fasted fish, resulting in nonsignificant differences in body composition among feeding treatments. The utility of BIA and Fulton’s K as condition indices requires differences in body composition. In our study, BIA measures were not significantly different among the three feeding treatments, and only on the final day of sampling was K of fasted vs. fed fish significantly different. BIA measures were correlated with body composition content; however,wet weight was a better predictor of body composition on both a content and concentration (% wet weight) basis. Because fish were growing isometrically, neither BIA nor K was well correlated with growth rate. For immature fish, where growth rate, rather than energy reserves, is a moreimportant indicator of fish condition, a nonlethal index that reflects shortterm changes in growth rate or thepotential for growth would be more suitable as a condition index than either BIA measures or Fulton�
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