Dietary phytase supplementation in rapeseed protein based diets influences growth performance, digestibility and nutrient utilisation in turbot (Psetta maxima L.)

In this study the performance of juvenile turbot (Psetta maxima L.) fed varying dietary phytase (Natuphos (R) 5000 G, BASF SE) supplementation levels was determined in a 56 day lasting growth trial, followed by a digestibility trial. One control diet (C) based on fish meal and three test diets based on rapeseed protein concentrate (RPC) were produced. RPC based diets contained phytase levels of 0 (P0), 1000 (P1000) and 2000 (P2000) FTU kg(-1). Feed intake and growth performance were significantly (p < 0.05) improved in fish fed P1000 and P2000 compared to fish fed unsupplemented P0. Furthermore fish fed P2000 showed a significantly improved performance level, comparable to the control group, with regard to FCR, PER and ADC of protein. Also the ADC of ash and phosphorus increased significantly due to phytase supplementation. In contrast, the ADC of other investigated minerals Ca, Mn, Fe, Co, Cu, Zn and Mg were not significantly affected. Moreover, slightly increased retention of nitrogen and significantly increased retention of phosphorus were observed in fish fed P2000 compared to fish fed P0. In conclusion, the supplementation of phytase to plant protein based diets rich in phytic acid increases nutrient digestibility and utilisation, which can positively influence growth performance and nutrient emissions in turbot production. Statement of relevance: To the best of our knowledge this is the first time that effects of dietary phytase incorporation were studied in turbot nutrition and the results consequently lead to a deeper insight and better understanding of this enzyme. The apparent digestibility coefficient (ADC) of protein and phosphorous increased significantly, which led to an improved growth and may lead to a more efficient utilisation of plant protein sources in turbot nutrition. Retention of nutrients (N & P) was also improved and gives the ability to a more sustainable turbot production via reduced phosphorus supplements/phosphorus contents in feeds and thus potentially decreased nutrient emissions in fish farm effluents. (C) 2015 Elsevier B.V. All rights reserved.