Fishmeal hydrolysation and non-protein energy sources affect the kinetics of nutrient digestion in the gastrointestinal tract of African catfish (Clarias gariepinus)

The kinetics of nutrients digestion and development of chyme characteristics in African catfish (Clarias gariepinus) were assessed in response to fishmeal hydrolysation and non-protein energy (NPE) sources. Four diets were formulated to contain starch or fat as NPE source, and fishmeal or hydrolysed fishmeal as protein source in a 2 × 2 factorial design. Juvenile African catfish (average weight, 63 g) were stocked in glass experimental tanks connected to a common recirculation aquaculture system and were fed restrictively for 3 weeks. Four hours after the consumption of a single meal, fish were dissected to collect chyme from the gastrointestinal tract (GIT). Chyme was collected from stomach, proximal- and distal intestine and analysed for dry matter (DM) content, crude protein (CP) and marker concentration. Postprandial water fluxes to the GIT and stomach evacuation were calculated using yttrium oxide (Y2O3) as an inert marker. Faecal DM and CP apparent digestibility coefficient (ADC) were determined by a marker method. Results showed that fishmeal hydrolysation had no effect (P > 0.1) on the DM content in all the GIT compartments. However, replacing dietary fat by starch resulted in a higher DM content in the stomach (P 0.1) but in the distal intestine, chyme DM was higher at the “fat diets” (P