Ingredient apparent digestibility coefficients for the Australian short-finned eel (Anguilla australis australis, Richardson)

Fish-meal is the most widely used protein source in commercial eel feeds and research evaluating alternative protein sources is lacking especially for species under current aquaculture development. This investigation was conducted to determine apparent digestibility coefficients of available plant and animal meals for the juvenile Australian short-finned eel (Anguilla australis australis Richardson). The suitability of a modified Guelph-type settlement faecal collector in eel digestibility studies was assessed. Animal by-product (meat; blood; poultry) and plant protein (soybean; canola; corn gluten; lupin; field pea) meals were mixed with a reference diet and marker (0.3:0.69:0.01) and the resultant test diets fed to the juvenile eels (3.15 plus or minus 0.42 g) at 5% BW/d. The reference diet and all the test diets were accepted and consumed at the fed ration. Apparent digestibility coefficients for crude protein (ADCCP) for all test ingredients were between 0.85 and 0.97. However, apparent digestibilities for dry matter (ADCDM) and energy (ADCkJ) were significantly (P<0.0001) higher for animal by-products than for plant proteins except for corn gluten meal. This was explained by the higher content of nitrogen free extractives in the former plant proteins. There were significant (P<0.01) positive correlations between ADCDM and ADCkJ (r = +0.98), ADCDM and ADCCP (r = +0.62) and between ADCCP and ADCkJ (r = + 0.55). Similar results obtained for warm water species using similar faecal collection techniques and limited digestibility data from eels supported the suitability of the modification of the Guelph-type settlement collector system.