2.6. Histology study
After 48 h of post-exposure to the extract inducing anesthesia at a concentration of 17.5 mg/l both the positive and negative controls were sacrificed immediately. Gill tissues were fixed in Bouin's solution (Roberts, 2001) for histological examination, dehydrated with graded series of ethanol solutions, cleared in xylene, embedded in paraffin blocks, and cut with a WESWOX-OPTIK MT1090A microtome. Then the sections were stained with Hematoxylin–Eosin stain. Histopathological changes were examined microscopically (Leica Microsystems, Germany).