Phytase on the digestibility of plant protein feed for silver catfish, Rhamdia voulezi

This study evaluated the effect of diet supplementation with phytase enzyme (1,500 IU kg(-1) of phytase) on the apparent digestibility parameters, availability and mineral deposits in the bones, intestinal histology, and proximate analysis on silver catfish (Rhamdia voulezi). A total of 360 silver catfish with an average weight of 236.98 +/- 54.02 g were randomly distributed in 24-500 L conical-cylinder aquariums. The experimental design was completely randomized, represented by eight treatments and three replications in a factorial design. The eight treatments included formulations based on three different plant protein sources (soybean meal, canola meal, and sunflower meal) and one reference diet, each set differentiated by supplementation or no supple-mentation with phytase. The best CDA values and availability of nutrients were identified in the diet containing soybean meal. The reference diet without phytase resulted in increased intestinal villus height, and the diet containing canola meal without phytase resulted in thicker intestine muscular layers. The proximate compositions between diets with and without phytase showed significant differences (p < 0.05); the different protein sources responded in different ways to the activity of phytase. The diet with soybean meal showed the highest nutrient digestibility, and phytase supplementation improved the availability of dietary calcium and magnesium. The inclusion of sunflower meal (30%) caused harmful changes in the intestinal villi of the Rhamdia voulezi.