Fish Necropsy is a thorough examination and dissection of a dead animal’s body to determine the cause of death. A conclusion can be reached after considering several observations.

Two images presenting the fish incision and lesions points. First image presents a black and white sketch of the fish seen from its left profile. Four incision lines create a rectangle structure on the side of the fish, which is supposed to be cut out to see the internal organs. First incision line stretches from the upper back fin to the upper part of the head of the fish. Second incision line stretches from the lower back fin to the lower part of the head of the fish. Third incision line stretches from the lower to the upper part of the head of the fish. Fourth and last  incision line stretches from the lower back fin to the upper back fin of the fish. Second image shows the presence of lesions, which are categorised into focal, multifocal and diffuse ones. All of the lesions are presented as yellow stains on the blue fish-shaped structures. Focal lesions are places at either abdominal region - between pelvic and anal fin, on the side, under the soft dorsal fin, or at the lateral line, just before caudal fin. Multifocal lesions can be present at abdominal region and at the side, under spiny dorsal fin, at the same time; under the soft dorsal fin and at the side, under spiny dorsal fin, at the same time; or at the lateral line, just before caudal fin, under spiny dorsal fin, under soft dorsal fin and between the head and pelvic fin, all four at the same time. Diffuse lesions happen at the centre of the side of the fish, little under the spiny dorsal fin, and they occur in multiple at the same time.

Good observations are descriptive and systematic. Examination should include:

  • The fish species, including length and weight

  • The condition of the fish (alive, moribund or dead)

  • The presence of any area of coloration

  • The color of the gills (healthy gills are bright, cherry red)

  • Parasite survey (skin scrape, gill biopsy or fecal sample results)

  • The presence of lesions

In general, freshly dead fish should have relatively clear eyes, good coloration, red to pink gills, and should not have a bad odor. The primary respiratory apparatus in fish is the gills. The gills enable maximum extraction of oxygen from the water and removal of carbon dioxide and ammonia from the blood.