A comparison between methods used to determine the energy content of feed, fish and faeces samples

Three different methods used to determine the gross energy content of feed, fish and faeces samples were compared. Method 1: the gross energy content was calculated from the chemical composition using values of 5.65, 9.45 and 4.2 kcal·g −1 for protein, fat and carbohydrates respectively. Method 2: the gross energy content was determined by combustion of about 0.9 g of each material in a bomb calorimeter. Method 3: the gross energy content was determined by dichromate wet oxidation of about 1.5 mg of each material. The chemical oxygen demand (COD) obtained was converted to energy, using a factor of 3.40 kcal per g COD, and corrected for incomplete oxidation of protein (0.95 kcal per g protein). The results indicate that the gross energy content of feed and faeces can be determined most accurately by combustion. Calculation from chemical composition will underestimate dietary and faecal gross energy content. The gross energy content of fish can be calculated accurately on the basis of protein (N-Kjeldahl × 6.25) and fat (hexane-extracted) content. Determination by dichromate wet oxidation underestimated the gross energy content of all three materials tested.