Danube salmon fry were fed eight experimental diets for 42 days at a water temperature of 16-degrees-C with continuous feeding and illumination. A total of 8% of the fish-protein carrier of a dry salmon starter diet was replaced by either freeze-dried zooplankton (copepods and cladocerans, ratio 1:6), freeze-dried Artemia cysts, freeze-dried beef muscle or heat-denatured freeze-dried zooplankton (copepods and cladocerans, ratio 1:6). In addition, a commercial Arctic charr dry starter diet was supplemented with 8% of freeze-dried zooplankton (copepods and cladocerans ratio 1:6). For control purposes the fry were also fed the unsupplemented salmon and Arctic chaff starter diets and an extruded salmon starter diet. At the end of the trial the mean survival and weight gain were significantly greater (P < 0.002) for fry fed the salmon and Arctic charr diets supplemented with 8% of freeze-dried zooplankton compared to the comparable control diets without any additive. Fry fed diets supplemented with 8% freeze-dried Artemia cysts, freeze-dried beef muscle and heat-denatured freezed-dried zooplankton did not have improved growth or survival (P > 0.05) relative to those receiving the unsupplemented salmon starter diets. Differences in the amino acid and fatty acid composition of the diets did not correlate with fish performance. A commercial extruded EWOS salmon diet resulted in the highest daily growth rate (5.2%) but fish mortality was 28.6% after 6 weeks. At the beginning of exogenous feeding, the stomach and intestine of Danube salmon were not fully differentiated. The development of the digestive tract was not completed until the 28th day, when the pyloric caeca were completely formed. The results suggest that the freeze-dried zooplankton may have been a source of exogenous enzyme activity during the time of first-feeding of Danube salmon fry.