2.8. Histopathological examination
Representative moribund tilapia (n = 3) from each challenge group and apparently healthy tilapia (n = 3) from the control groups were examined for histopathological changes. Tissues of affected fish (spleen, kidney, liver, and brain) were collected and preserved in 10% buffered formalin. After fixation for 24 h, sampled tissues were dehydrated in an ethanol series, embedded in paraffin, and sectioned at 5 µm thickness. The sections were then stained with hematoxylin and eosin, following the standard histological protocol. Histopathological changes were examined under a light microscope equipped with a digital camera (Olympus, Tokyo, Japan).