Relationship between intestinal brush border enzymatic activity and growth rate in tilapias fed diets containing 30% or 48% protein

The effects of feeding juvenile crossbred tilapias diets containing 30% (LP) and 48% (HP) protein on the activity of intestinal brush border enzymes and on their growth performance were evaluated. Several groups of tilapia were reared in intensive fresh water re-circulating tanks under controlled conditions. The F1 hybrid O. mossambicus×O. aureus exhibited the highest growth rate while the F2 (F1×F1) hybrid had the lowest, among the examined crossbreeds, irrespective of the protein level in the tested diet. The specific growth rate (SGR) was not influenced by the interaction between the food type and the genetic background, while the SGR of all the genetic groups was higher when HP diet was consumed. The food type had an additive effect, without a reciprocal interaction with the genetic background, on the enzymatic activity of maltase and γ-glutamyl transpeptidase (γ-GT). A significantly higher activity of maltase was detected in both the lower and upper intestinal parts of fish that consumed the HP diet compared with the activity detected in the lower section of fish that consumed the LP diet. The activity of γ-GT in the entire intestinal tract was significantly higher in the LP diet than in the HP diet. The activity of alkaline phosphatase was significantly higher in the upper compared with the lower intestinal section. Among the different species, the activity of maltase and γ-GT and the activity of AP in the HP diet was the highest in the F2 hybrid. Leucine amino peptidase was the only enzyme that was not affected by the composition of the food or the genetic background and its activity was not found to differ between the intestinal sections. The variability in the activity of digestive enzymes of different aquacultured hybrids fed artificial diets revealed in this study provides some insight into the role of enzymatic activity and its effect on food utilization and growth rate of these tilapias.