Response of Rhinogobio ventralis skin to Ichthyophthirius multifiliis infection: pathological, transcriptomic and metabolomic analyses

Rhinogobio ventralis is a typical endemic fish and an important economic species in the upper reaches of the Yangtze River. However, it is highly susceptible to Ichthyophthirius multifiliis (Ich) during artificial breeding, resulting in elevated mortality rates following infection. In this study, we established an infection model using Ich to investigate its effects on the skin of R. ventralis. Pathological changes on the skin were examined through tissue sections and transmission electron microscopy. The results showed a significant increase in mucus cells, club cells and epidermal thickness, the abnormal desmosome junction between epithelial cells, mucous cells pyknosis shrinkage along with morphological and structural abnormalities in their organelles within the skin after infection. We employed transcriptomics and metabolomics to characterize key genes, metabolites, and signaling pathways in the skin following Ich infection. A total of 84,016 unigenes and 1075 metabolites were obtained from skin tissues. Respectively, 388 DEGs and 135 differentially expressed metabolites, 233 DEGs and 72 differentially expressed metabolites were obtained at 7 dpi and 14 dpi, respectively. In response to Ich infection, the host modifies the ribosome pathway, protein processing in endoplasmic reticulum pathway, antigen processing and presentation pathway and glycerophospholipid metabolism, which suggests both disruption and activation of the immune system, alongside disruptions in metabolic processes among infected R. ventralis. Our results shed light on the immune strategies employed by R. ventralis in response to Ich infections, thereby providing a valuable dataset for further investigation into the mechanisms underlying resistance regulation in R. ventralis against such infections.