Effects of an acute negative and positive stimulus on immune-related gene expression in the pituitary and head kidney of carp (Cyprinus carpio L.)

The objective of this study was to investigate expression profiles of genes involved in the immune responses in the head kidney, as well as stress response-related genes in the pituitary in juvenile koi carp after exposure to an acute positive (feed reward) or negative cue (air exposure). Both, the head kidney and the pituitary transcriptome analysis, revealed distinct gene expression patterns in fish subjected to the different treatments. Notably, expression changes of genes with the greatest impact on the fish's stress status were identified, emphasizing their role in stress perception and immune regulation related to stress. This allows the identification of promising candidates for further investigations. Additionally, the application of ElasticNet regression enabled, with high accuracy, the classification of stimulus presence, absence and valence, based on the gene expression patterns, representing a novel and valuable tool for transcript analysis in stressed fish. To our knowledge, the ElasticNet regression was used for the first time in such an application. These findings further confirm the differential perception and response of fish to negative and positive stimuli, offering insights into the complex interplay between stress and immune responses.