Optimizing methodological aspects of stool collection by sedimentation in digestibility studies with pirarucu (Arapaima gigas)

This study aimed at optimizing the sedimentation method for stool collection in digestibility tests in pirarucu. In the first trial, juvenile fish (435.26 ± 10.80 g) received the reference diet with chromium oxide to determine the gastrointestinal transit time (GITT). In the second, the fish were fed the reference and two test diets (corn and soybean meal) for 15 days. The apparent dry matter, protein and phosphorus digestibility coefficients (ADC) were determined to verify the time of acclimatization to the experimental diets. The stool pattern was visually analysed on day 5 and 10 of acclimatization. The third trial evaluated the maximum stool collection time for reduced nutrient leaching 30 min, 1, 6 and 12 h after evacuation as well as the stool collected directly from the rectum. GITT was 5.5 h. ADC varied during the initial acclimatization and stabilized between days 8 and 10, corroborating a consistent visual pattern on day 10 than on day 5. Nutrient ADC increased with increased stool collection time, except with a 30‐min interval, which presented ADC similar to rectum samples. Pirarucu stool must be collected from day 10 for a 30‐min interval about 30 min after the second daily meal.