Digestive enzymatic profile of Dentex dentex and response to different dietary formulations

Digestive physiology of on-growing common dentex (Dentex dentex), including protease, amylase and lipase activity in stomach, pyloric caeca, anterior and posterior intestine, was evaluated. The influence of dietary macronutrient balance on these digestive processes was also assessed. Four experimental diets with different protein:lipid:carbohydrate ratios (43/16/28; 43/24/4; 38/19/28 and 38/24/13) were formulated. The highest activity for acid proteases was located in the stomach at pH 1.5. Alkaline proteolytic activities showed the highest values in the pyloric caeca and posterior intestine at pH 8.5-9.0. Dentex showed substantial amylase activity in the pyloric caeca and posterior intestine. Lipase activity was higher in the pyloric caeca, anterior and posterior intestine and was not detected in the stomach. Feed composition influenced alkaline protease activity in the anterior and posterior intestine and was higher for the diet with less protein and more carbohydrates. Enhanced amylase activity was observed in the pyloric caeca and posterior intestine in those groups fed on higher carbohydrate and lower lipid level diets. High dietary carbohydrate levels produced the highest lipase activity but this only occurred in the anterior intestine. We can conclude that the digestive tract of dentex adapts well to protein digestion and possesses a high potential for digesting the other dietary macronutrients, too. Dietary carbohydrate content seems to induce changes in protease, amylase and lipase activity.