Nutrient digestibility for juvenile silver perch Bidyanus bidyanus: development of methods

Three experiments were undertaken to develop methods for determining digest ible energy, dry matter and protein of diets and feed ingredients for juven iles (5-15 g/fish) of the Australian freshwater fish, silver perch. The fir st experiment compared stripping, dissection and settlement as methods of c ollecting faeces. Stripping was not a suitable method for collecting digest a from juvenile silver perch less than or equal to 10 g/fish; insufficient sample was obtained and regurgitation of food contaminated samples. Digesti ble dry matter calculated using digesta collected by dissection were lower than values using faeces collected following settlement. Values using diges ts extracted from the posterior portion of the intestinal tract were higher than those using digesta from the anterior portion. In the second experime nt, separate digestibility coefficients (DC) were calculated using faeces c ollected 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 inc reased with time. Digestible dry matter was similar when calculated using f aeces 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 faec es 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 peri ods. This indicated that leaching did not affect digestible coefficients af ter 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 suitabl e method for determining digestibility in juvenile silver perch. (C) 1999 E lsevier Science B.V. All rights reserved.