Digestible Energy: Methodological Influences and a Mode of Calculation

Abstract

The energy values of fish feed could be a suitable indicator for choosing an appropriate diet for a particular species. This study examined the effect of fish size, water temperature and time of feces collection on energy digestibility. In addition, energy digestibilities of practical diets and commercial feeds were determined to find out if digestible energy (DE) values could be calculated from gross energy (GE) values. The DE determinations should preferably be conducted on carp weighing about 10 g maintained at around 20°C and with rainbow trout weighing less than 100 g at a water temperature between 10-15°C. The digestibility of energy increased in proportion to the lapse of time of fecal collection, until about 18 h in rainbow trout and even beyond that in carp, due to the leaching of nutrients. It was also confirmed that there was no change in the energy digestibility of fish over time. Comparing the energy digestibility of practical and commercial diets for carp, it was found that the average figure was 80%, proving that the DE of diets could be estimated from the GE values.