Gene expression profiling supports the welfare evaluation of rainbow trout (Oncorhynchus mykiss) reared under different environmental and management conditions in six commercial flow through systems

Abstract

The species-appropriate treatment of fish is of great importance and requires the accurate assessment of the fish welfare. Aim of this study was to get a deeper insight into the welfare of rainbow trout (Oncorhynchus mykiss) during grow-out on six farms equipped with flow through systems, each providing different environmental (water supply, and -exchange, water quality) and management conditions (stocking density, feeding frequency). The mRNA levels of 91 genes involved in stress and immune responses were analysed using multiplex quantitative PCR and complemented with organ histopathology, blood glucose and lactate levels, organ somatic indices, external morphological damage, behaviour, as well as environmental and management conditions. The farms analysed revealed large differences in environmental and management parameters. Accordingly the expression profiles of distinct sets of genes and other welfare indicators differed significantly between farms. Generally, fish from farms with a high water supply and fast water exchange at lower stocking densities had lower levels of external morphological damage. Stocking density and the duration of a total water exchange in the tank revealed a significant impact on gene expression. Further, effects of water quality and immunological responses were observed. The gene expression profiles obtained provide a deeper insight on the stress and immune response influenced by different rearing conditions, and hence a more accurate status of trout welfare in aquaculture settings.