Experiments were conducted to determine the effectiveness of measuring feed consumption and excretion in salmonid fish by radiographic and chemical indicator methods. To do this it was also necessary to measure concurrently the digestibility. Digestibility was determined in 16 diets of different origin comparing n-alkanes (C28 and C32) as indigestible indicators with chromium sesquioxide and celite. Research was also conducted comparing the radiographic method for measuring feed intake with that of using C32 alkane as an external indicator to measure faecal output. The results show that n-alkanes can be used as internal and external indicators in measuring faecal output, digestibility and intake in fish. The radiographic method and the n-alkane indicator method are compatible for the measurement of feed consumption, but both methods give high variability, making small differences in feed consumption difficult to detect.

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