Developmental Changes in the Activity of Major Intestinal Brush Border Enzymes in the Wild Juvenile Nile Perch, Lates niloticus (Linnaeus, 1758)

The Nile perch, Lates niloticus is a carnivorous fish and a potential candidate for aquaculture. The ability of fish to utilize ingested nutrients depends on availability of appropriate enzymes along the intestinal tract and can be used in the formulation of artificial diets. The effect of fish size (total length) on the activity of three brush border enzymes was evaluated. Juvenile Nile perch at different stages of development were captured from the shores of Lake Victoria and the activity of three brush border enzymes in three intestinal sections (pyloric caeca, upper and lower intestine) in six different size groups evaluated. Two proteolytic enzymes, leucine aminopeptidase (LAP, EC 3.4.11.1), gamma glutamyl transferase (γ-GT, EC 2.3.2.2) and a carbohydrase (maltase, EC 3.2.1.20) were assayed. All the three enzymes were influenced by the fish size, intestinal section and the interaction between the two factors (p< 0.05). The highest specific activity of LAP and maltase was observed in the upper intestine while that of γ-GT was highest in the lower intestine. The specific and relative total enzyme activities were significantly higher (p< 0.05) in the 11-15 and 16-20 size groups in all the tested enzymes. Total enzyme activity for all the enzymes increased with fish size. There was a significant correlation (p< 0.05) between the tested enzymes with the highest correlation between LAP and maltase, this correlation was highest in the pyloric caeca. The results of the present study reveal that, the most critical stage in the nutrition of juvenile Nile perch occurs when the fish attains a total length of 11-20cm. This stage (11-20cm) necessitates intensification in the feeding regime through incorporation of high protein and carbohydrate rations. Presence of maltase indicates that this fish can utilize lower levels of carbohydrates in the diet.