The Nile perch, Lates niloticus is a carnivorous fish and a potential candidate for aquaculture. The relationship between fish size (total length) and the activity of three brush border enzymes: leucine aminopeptidase (LAP), γ-glutamyl transferase (γ-GT) and maltase was evaluated in six size groups (1 to 5, 6 to 10, 11 to 15, 16 to 20, 21 to 25 and 26 to 30 cm) of wild juvenile Nile perch. Enzymatic activity was evaluated in three intestinal sections: pyloric caeca, upper intestine and lower intestine. 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 enzyme activities were significantly higher (p< 0.05) in the 11 to 15 cm and 16 to 20 cm size groups in all the tested enzymes. The results reveal that, the most critical stage in the nutrition of juvenile Nile perch occurs when the fish attains a total length of 11 to 20 cm. Dietary formulations for this species should hence be in cooperate substantive amount of proteins and carbohydrates at this stage so as to maximize weight gain. The presence of maltase is an indicator that carbohydrates cannot be precluded from formulated diets for this species.
Key words: Nile Perch, enzyme activity, aquaculture, brush border.