Non-invasive epidermal mucus RNA-Seq analysis for the development of evaluation methods of physiological effects of environmental stress on Japanese eel

Environmental changes in rivers caused by water temperature fluctuations and more extreme rainfall associated with climate change are concerned to affect the physiological impacts (environmental stress) on wild Japanese eels. This project focused on the epidermal mucus of Japanese eel, which can be sampled non-invasively in the field, and investigated whether RNA-Seq analysis could reveal the physiological state of this species in response to environmental stresses. We first compared the transcriptome (RNA-Seq) of the epidermal mucus of Japanese eel under normal conditions with tissues in direct contact with the external environment (skin, muscle, caudal fin, and gills) to investigate the characteristics of genes expressed in the epidermal mucus. Next, we set up tank trials simulating (1) suspended solids (SS) stress due to sediment runoff caused by heavy rainfall (with kaolin cray addition) and (2) water temperature changes (10°C, 20°C, and 30°C) as physical stresses on wild Japanese eel caused by climate change. Then, we performed RNA-Seq analysis to identify genes in the epidermal mucus, skin, gills, and liver responding to each environmental stress.