Histology involves the microscopic examination of thin, stained tissue sections in order to study their structure and function and to determine changes which may be due to pathogens and disease (histopathology). Following sampling, BC CAHS prepares fish tissues to be fixed, embedded in paraffin, cut with a microtome, and mounted on slides. A qualified histopathologist then examines the slides with light microscopy for any tissue changes resulting from infectious or non-infectious diseases.