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Three trials, with classical experimental designs for in vivo digestibility studies, were conducted to determine the apparent digestibility coe⁄cient (ADC) of protein (ADCp), lipid (ADCl), energy (ADCe) and amino acids (AA) in selected animal by-products fed to European sea bass, Dicentrarchus labrax (Trial 1), gilthead sea bream, Sparus aurata (Trial 2), and turbot, Psetta maxima (Trial 3). In each trial, ¢ve experimental diets [including a reference diet (RD)] where ¢sh meal (FM) was used as the sole protein source were fed ad libitum to the ¢sh for a period of 4 weeks. Test diets were based on the FM RD and obtained by replacing 30% of the RD with a category III designated European animal by-products (¢t for human consumption), namely: steam hydrolysed feather meal (HFM), enzyme-treated feather meal (EFM), poultry meat meal (PMM) and spray-dried haemoglobin meal (SDHM). Faecal material was collected using the 'Guelph system' , and nutrient and energy digestibility coe⁄cients were related to the measurement of chromic oxide (Cr 2 O 3 ) incorporated into the diet at a rate of 0.5%. Without any exception, FM diets yielded the best digestibility values for all macro-nutrients and by all ¢sh. Among the test ingredients, ADCp was consistently higher for PMM and SDHM in the three species (85.5%, 91.1% in sea bass;79.2%, 82.8% in sea bream; and 78.4%, 74.8% in turbot). Conversely, ADCp of HFM and EFM were less e⁄ciently digested (67.2%, 68.2% in sea bass; 21.5%, 21.7% in sea bream; and 46.6%, 36.0% in turbot). However, the novel processing method applied to feather meal did not considerably in£uence the digestibility of most of the nutrients in this feedstu¡. The current investigation yielded valuable numerical ADC for EAA considered to be of prime importance in generating balanced diet formulations.

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