*2.3. HE Staining of Tissue Sections*

The tissue samples of the gills and skin stored in 4% paraformaldehyde were sent to Servicebio Biotechnology Co., Ltd. (Wuhan, China) for paraffin embedding, tissue sectioning and HE staining. The HE-stained sections were observed under a microscope (ZEISS Axio Scope A1, Jena, Germany) and photographed.
