Apparent digestibility of selected ingredients in diets for juvenile grouper, Epinephelus coioides (Hamilton)

Abstract

Apparent digestibility coefficients (ADCs) for dry matter (ADC_dm) and crude protein (ADC_cp) of selected feed ingredients were determined in vivo for grouper using passive faeces collection (Guelph System). A reference diet (RF) and test diets (consisted of 70% RF and 30% test ingredient) with 1% Cr₂O₃ as an inert indicator were used. An RF contained 45% protein, 10% fat and 15.7 kJ g⁻¹ metabolizable energy. Three isonitrogenous and isocaloric diets, each contained a test ingredient (white fish meal, white cowpea meal and ipil-ipil leaf meal), were used in a growth study based on ADC_cp of feed ingredients. An RF without Cr₂O₃ was a control. The ADC values of experimental diets were also determined. In grouper, the ADC_dm of white cowpea meal, defatted soybean meal, wheat flour and shrimp meal (74–76%) were significantly lower than that of squid meal (99%), but comparable with those of the fish meals (84–89%). No significant difference was observed between the ADC_dm of ipil-ipil leaf meal, rice bran and wheat flour (56–73%). The ADC_cp of white cowpea meal and defatted soybean meal were similar to those of the fish meals, squid meal and shrimp meal (94–99%). The ADC_cp of wheat flour was comparable with that of ipil-ipil leaf meal (79–83%). Rice bran had the lowest ADC_cp value of 43%. Based on specific growth rate (SGR), the growth of fish fed white cowpea meal-based diets was similar to that of the control fish (3.2–3.3% day⁻¹). Also, no significant difference was observed between the ADC_dm (68–72%) and ADC_cp (88–91%) of white cowpea meal-based diet and the control diet. The results suggest that ADC values can be used as indicators to determine the nutritional value of feed ingredients. White cowpea meal can be incorporated as a protein source in practical diet for grouper at 20.5% of the diet with no adverse effect on growth.