Abstract
Three experiments were undertaken to develop methods for determining digestible energy, dry matter and protein of diets and feed ingredients for juveniles (5–15 g/fish) of the Australian freshwater fish, silver perch. The first experiment compared stripping, dissection and settlement as methods of collecting faeces. Stripping was not a suitable method for collecting digesta from juvenile silver perch ≤10 g/fish; insufficient sample was obtained and regurgitation of food contaminated samples. Digestible dry matter calculated using digesta collected by dissection were lower than values using faeces collected following settlement. Values using digesta extracted from the posterior portion of the intestinal tract were higher than those using digesta from the anterior portion. In the second experiment, separate digestibility coefficients (DC) were calculated using faeces collected by settlement every 2 h (up to 18 h) after tanks were cleaned and these were compared with DCs calculated using faeces collected 6, 12 or 18 h after tanks were cleaned. Digestible energy and digestible dry matter increased with time. Digestible dry matter was similar when calculated using faeces collected over 12 or 18 h and greater than for faeces collected over 2 or 6 h. Digestible energy and digestible dry matter calculated using faeces collected every 2 h and averaged to give a value for 6, 12 or 18 h were similar to values calculated using faeces collected over 6, 12 or 18 h periods. This indicated that leaching did not affect digestible coefficients after faeces had settled. The third experiment validated the assumption that DCs for juvenile silver perch for different feed ingredients are additive. The sum of DCs calculated separately for individual ingredients was similar to that calculated for a diet composed of those ingredients. These results demonstrate that collection of faeces by settlement over 18 h is a suitable method for determining digestibility in juvenile silver perch.
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