Feeding fish according to organic aquaculture guidelines EC 710/2009: Influence of potato protein concentrates containing various glycoalkaloid levels on health status and growth performance of rainbow trout ( Oncorhynchus mykiss)

A feeding trial was conducted to evaluate the effect of potato protein concentrate (PPC) replacing fishmeal in nutrition of rainbow trout ( Oncorhynchus mykiss) according to organic aquaculture guidelines. Eight diets were formulated by partial replacement of fishmeal (25%, 50%, 75% and 100%) with PPC of two different qualities (LG-PPC with low glycoalkaloid content of 7.41 mg kg − 1 dry weight, HG-PPC with high glycoalkaloid content of 2150 mg kg − 1 dry weight) and one experimental diet without PPC served as control. Experimental diets were fed over a period of 84 days to triplicate experimental groups until apparent satiation. Best growth performance was observed in the control group. The inclusion of LG-PPC resulted in significantly reduced feed intake, feed utilization and growth with increasing replacement of 25% and higher. Increasing amount of dietary LG-PPC inclusion resulted in alterations in liver histology and in anterior intestine indicating an impact of glycoalkaloids on the different gastrointestinal tissues. The HG replacement revealed most prominently a decreased feed intake and growth parameters indicating massive undernourishment. Congruently, hypotrophy of the liver with ceroid pigment accumulation, and villi degeneration in the intestine were observed in all HG groups. Blood parameters were equally affected by an inclusion of PPC (LG and HG) in the diets involving reduced plasma TG (HG75), glucose (HG100) as well as protein (HG100). As a conclusion PPC as alternative protein in fish nutrition is only feasible with LG contents as HG diets resulted in severe undernourishment of fish, lowest growth performance and irreversible intestinal damages.