The aim of this research was to determine the effect of using phytase, carbohydrases (NSPases), and protease in a diet for juvenile rainbow trout Oncorhynchus mykiss on their productive performance and nutrient apparent digestibility coefficients.
Seven isoproteic (42% CP) and isocaloric (20% EE) experimental diets were formulated to meet the nutritional requirements of rainbow trout and evaluated under a completely randomized design. Soy-derived protein ingredients made up 30% of the final formulation, with 25% corn gluten and only 10% fishmeal. The diets were identified as follows: C, Control: No exogenous commercial enzyme addition; M: Diet C + β-mannanase (100,000 BMU kg-1); F: Diet C + Phytase (4,000 FTU kg-1); FM: Diet F + β-mannanase (100,000 BMU kg-1); FMX: Diet FM + Xylanase (4,000 XU kg-1); FMXG: Diet FMX + β-glucanase (500 BGU kg-1); FMXAP: Diet FMX + Amylase (400 AU kg-1) + Protease (8,000 PU kg-1). The experiment involved 25 fish tank-1. It was carried out in 21 tanks of 300 L under a RAS with continuous removal and filtration of feces. Chromium oxide, as an inert marker, was confirmed in diets and determined in feces. All procedures were performed in accordance with the reference guidelines of the Guide for the Care and Use of Laboratory Animals. Once the assumptions of normality and homoscedasticity were verified, the data underwent an analysis of variance (ANOVA).
Results are shown in Table 1. The FMXAP diet achieved the best productive indices but did not statistically differ from the performance seen with phytase alone, with the only exception of crude protein digestibility.
Phytase supplementation consistently improved performance, primarily by enhancing the apparent digestibility coefficient of phosphorus and calcium, and their subsequent deposition in fish. The co-supplementation of NSPases did not yield further significant productive performance enhancements in the evaluated treatments indicating no evidence of the insoluble NSP-mediated ’cage effect’ or adverse effects from soluble NSP at these concentrations. Finally, the addition of protease at the dose employed promoted protein digestibility. These findings, therefore, augment the scarce yet encouraging current literature regarding protease supplementation, underscoring the necessity and potential for deeper exploration in this research line.