Welfare and quality of farmed trout fed high plant protein diets. 3 alternative indicators to evaluate stress in fish

AbstractPrevious studies reported that diets can increase tolerance to various stressful conditions in different fish species. Consequently, the present work evaluated the effects of replacing fish meal (FM group) with an 80% of plant protein source (PV 80 group) in the diet of farmed rainbow trout (Oncorhynchus mykiss) on stress response caused by two different slaughter methods (electrical stunning and asphyxia). Plasma cortisol levels are widely employed as quantitative measure of stress (Wendelaar Bonga, 1997). However, to avoid the blood sample, it would be useful to test less invasive alternative biological matrixes such as skin mucus, faeces and caudal fin to use them especially in live fish and also invasive matrixes as muscle for post-slaughter analysis. From each experimental group twelve fish were netted, six were slaughtered by electrical stunning and six by asphyxia. From each fish, plasma, skin mucus, intestinal content, caudal fin tip and muscle were rapidly collected and frozen for cortiso...