Apparent digestibility comparison in rainbow trout (Oncorhynchus mykiss) assessed using three methods of faeces collection and three digestibility markers

Experiments were undertaken to investigate the apparent digestibility coefficient (ADC) of a range of macro- and micronutrients in rainbow trout using three external digestibility markers (chromic oxide, acid insoluble ash an titanium dioxide, alone or in combination), and three methods of faeces collection (modified Guelph system, St-Pee system and abdominal massage; hereafter referred to as 'column' 'collect' and 'strip, respectively). For each method of faeces collection, three replicate tanks of fish were acclimated for 5 days to a practical diet containing the external marker followed by 5 days of faeces collection. Both marker type and collection method significantly influenced ADC estimate in a similar manner for dry matter, protein, nitrogen-free extract, ash and energy. The ADC was consistently highest For the column and lowest for the strip methods of collection, and titanium dioxide gave higher ADCs vs. the other markers. Lipid ADC did not differ between the column and collect methods, but collection of faeces by the strip method gave lower ADCs, irrespective of marker type. In general, nutrient ADC was higher with the combined markers than when single markers were employed. The influence of marker type and collection method was less clear for the individual minerals studied.