Internal and External Examination
Before a necropsy is performed, fish should be euthanized with an overdose of anesthetic (e.g. MS 222, benzocaine or AQUI-S). Very occasionaly, other methods are used, such as brain spiking or ice slurries, but these should only be performed by someone with experience.
(Image 2: Anatomy of juvenille salmon. Aquatic Animal Health, Product Integrity Animal and Plant health, view 10th October 2014, (http://library.enaca.org/Health/FieldGuide/html/ts.htm#)).
(Image 3: Examination of gills, part of external examination)
External Handling (Necropsy):
- Examine the eye, mouth, nares, opercula, gills, pectoral fins, lateral line, pelvic fins, anal fin, caudal fin, dorsal fin, vent and caudal peduncle, to identify and record major changes to the exterior of the fish. (Examples may include ulcerations, skeletal deformity, exophthalmia (pop-eye), fin erosion, discolouration).
- Record the weight and length of your specimen
(Image 4: Barramundi Internal necropsy examination)
- Remove excess mucous off ventral surface off fish with a clean paper towel
- Sterilise the ventral aspect of the fish, as well as the work bench with a 70% alcohol spray
- Remove the operculum and examine the gill arches (looking at the colour and size)
- Remove the second gill arch and place in formalin (a colourless solution of formaldehyde in water, used as a preservative for biological specimens)
- Examine the other arches by slowly peeling them apart as if pages of a book
- Dissect out the eye
- Make an incision, immediately anterior of the vent and extend along the ventral midline to the operculum. Don’t use the vent to begin your incision because it will contaminate the specimen with fecal material (extreme care should be taken with incisions to avoid damage to internal organs)
- The second incision also commences at the vent, but is passed cranidorsally in line with the dorsal margin of the peritoneal cavity, ending at the dorsal end of the gill opening
- The third cut joins the two incisions together, which allows for removal of the body wall and reveals the internal organs
- Identity internal organs including, heart stomach, intestine, spleen, liver, gonad (if present), kidney, swim bladder
- In order to collect histopathology samples, remove a small section of each organ and place in a labeled bottle of 10% formalin to preserve (include: gill, muscle section with skin, posterior kidney, anterior kidney, liver stomach, intestine, spleen)
(Image 5: Barramundi or Sea Bass labelled diagram. ecoGROW (2010), viewed 15th October 2014, (http://www.ecogrow.ca/Aquaculture/Barramundi_species_data.htm)).