The influence of Nu pro® as a substitution of fish meal on the growth performance of rainbow trout (Oncorhynchus mykiss W.) cultivated in recirculating system.

The purpose of the study was to determine the effect of the addition of NuPro® as a substitution of fish meal in feeding of rainbow trout (O. mykiss) on the functional properties of extruded feed as well as on growth intensity, blood biochemical and meat quality parameters in experimental fish, cultivated in recirculating system. Rainbow trout received extruded feed (2.5 mm pellets), produced by extrusion process in “University of food technologies – Plovdiv”. Two hundred and twenty five rainbow trout were divided into three groups: control (A), experimental B and C, each of them with three replicates, with a mean initial live weight, respectively 24.3±7.3, 24.3±7.3 and 24.4±8.5 g. The feed content for fish from experimental groups was as follows: for the control group (A) – without Nu Pro, for the group B – 33% fishmeal and 7% Nu Pro®, and that for the group C 25% fishmeal, with a content of 15% Nu Pro. The duration of the trial period was 60 days. The addition of Nu pro® on functional properties of extruded feed was retraced. At the end of the experiment, fish growth (g), their survival (%) and feed conversion ratio (K) were calculated. The blood biochemical and meat quality parameters in fish from experimental groups were also measured. The evaluation of functional properties in extruded feed showed that the use of Nu Pro® as a substitute of fishmeal has a number of advantages that include-increasing the mass flow rate during extrusion, reducing the energy consumption during extrusion, increasing shelf life due to the higher absorption index. The main disadvantage that can be indicated is the faster dissolution of the product in contact with water. At the end of the experiment, with the live weight, being highest in the rainbow trout from the experimental group (C) – 69.76±25.41 g, followed by that of fish from the experimental group (B) – 67.82±20.00 g and this one of individuals from group (A) – 64.01±17.07 g and the statistical differences haven`t been proven (p > 0.05). The supplementation of feed with NuPro® in the diet of rainbow trout decreased the level of alkaline phosphatase (ALP), cholesterol and triglycerides respectively with 9.29%, 16.4% and 9.47% compared with the values of these parameters in fish from control group, but the differences were not significant (P ≥ 0.05). The partial replacement of fish meal with Nu Pro® in rainbow trout did not affect the meat quality parameters.