Potential biomarker genes for crowding stress in maraena whitefish Coregonus maraena

Stress represents a major factor negatively affecting fish welfare in aquaculture. The objective of the present study was to identify and evaluate informative indicators for the welfare and particular health status of maraena whitefish (Coregonus maraena) farmed at four different stocking densities. Transcriptome profiling revealed that numerous stress-related signaling pathways were activated in liver and kidney under ED and HD conditions, such as ERK/MAPK, mTOR, glucocorticoid receptor, SAPK/JNK and JAK/Stat signalling, as well as p38 and p53 signalling. Moreover, several stress-relevant effector pathways were found to be overexpressed including glycolysis and glycogen degradation. Strikingly, a high number of upregulated genes in kidney and in liver of fish kept at HD (compared to MD fish) were related to immunological processes, such as Acute-phase response signalling, B cell receptor signaling, CD28 signaling in T helper cells, and Interleukin-6 signaling. Four stocking density conditions were investigated: an uncrowded “moderate” density (MD: 33 kg trout/m³) , an elevated density (ED: 60 kg/m³ ), a low density (LD: 10 kg/m³ ), and high density (HD: 100 kg/m³). The experiment was performed twice, randomly assigned to identical glass tanks with MD (100 individuals), ED (180 individuals), LD (30 individuals), and HD (300 individuals). Trout were sampled 8 d after experimental onset.