Most of the abdominal organs can be removed by cutting
the oesophagus and lifting with forceps from that end,
pulling the gut and associated organs and making a further
cut near the vent. In this manner the intestinal tract, liver,
spleen, pancreas, and swim bladder are removed out of the
fish, leaving the gonads, attached anteriorly, and the kidney
remaining within the carcass. Complete removal of the
viscera is practical for easier assessment under a dissecting
microscope e.g. for parasitological analysis, however inappropriate, if aseptic microbiological samples are required.
All the organs can be sampled for histology without removing them from the body cavity.
The salmon liver may vary in colour depending of the type
of diet (farm and wild fish), as well as the health status of the
fish. A sample should include a portion of the capsule (e.g. the
tip of a lobule) and should be collected using a sharp scalpel
rather than scissors. Avoid tearing liver tissue or accidentally
puncturing the gall bladder, as rough handling can release bile
which results in degenerative changes and artefacts (see
Fig. 4.31). Record any abnormal colour, suspicious or new
growths, fatty changes, the aspect of the cut surface, as well as
the appearance of the bile. Inspect the spleen, usually at the
posterior curve of the stomach or slightly further back and
similarly, take a sample for histology. An examination of the
gastrointestinal tract, pyloric caeca and associated pancreatic
tissues can be carried out once relevant microbiological sampling has been performed. The gastrointestinal tract can be
opened to expose the lumen and allow examination of the
mucosa and irregularities should be noted. Several pyloric
caeca with associated fat should be removed, thus allowing
examination of that portion of the gastrointestinal tract.
Additionally, a piece of the stomach and other portions of
the intestine may also be sampled. The swim bladder is
normally a transparent to opaque, whitish coloured organ.
Any change in colour, thickening of its wall, haemorrhage
or presence of fluid should be recorded. Evaluation of the
gonads provides information on the sex of the fish and degree
of maturation and a sample for histological assessment can be
performed slicing a section not thicker than 1 cm. Bouin’s
fixative has been recommended for this tissue as gonads in an
advanced stage of development can be hard to cut after
routine formalin fixation.
The kidney can be examined after the swim bladder has
been moved aside. Many infectious and non-infectious
conditions impact on the kidney and possible changes
include colour abnormalities, swelling, haemorrhage or a
granular appearance. Both the cranial and caudal areas
should be sampled for light microscopy avoiding
compressing the tissue by cutting first the peritoneal sheet
before attempting to lift the sample.
Maintaining an organised and systematic approach to the
necropsy is an important aspect of the procedure, and careful
observations made during this examination will provide
valuable information not only immediately, but consequently during the interpretation of the histological sections.
All tissues samples must be clearly identified with a reference code when sent for processing to ensure that there is no
risk of incorrect reporting.
Words of wisdom: ‘A poorly performed necropsy cannot be improved at a later stage’
3.3 Necropsy Procedure
31
the oesophagus and lifting with forceps from that end,
pulling the gut and associated organs and making a further
cut near the vent. In this manner the intestinal tract, liver,
spleen, pancreas, and swim bladder are removed out of the
fish, leaving the gonads, attached anteriorly, and the kidney
remaining within the carcass. Complete removal of the
viscera is practical for easier assessment under a dissecting
microscope e.g. for parasitological analysis, however inappropriate, if aseptic microbiological samples are required.
All the organs can be sampled for histology without removing them from the body cavity.
The salmon liver may vary in colour depending of the type
of diet (farm and wild fish), as well as the health status of the
fish. A sample should include a portion of the capsule (e.g. the
tip of a lobule) and should be collected using a sharp scalpel
rather than scissors. Avoid tearing liver tissue or accidentally
puncturing the gall bladder, as rough handling can release bile
which results in degenerative changes and artefacts (see
Fig. 4.31). Record any abnormal colour, suspicious or new
growths, fatty changes, the aspect of the cut surface, as well as
the appearance of the bile. Inspect the spleen, usually at the
posterior curve of the stomach or slightly further back and
similarly, take a sample for histology. An examination of the
gastrointestinal tract, pyloric caeca and associated pancreatic
tissues can be carried out once relevant microbiological sampling has been performed. The gastrointestinal tract can be
opened to expose the lumen and allow examination of the
mucosa and irregularities should be noted. Several pyloric
caeca with associated fat should be removed, thus allowing
examination of that portion of the gastrointestinal tract.
Additionally, a piece of the stomach and other portions of
the intestine may also be sampled. The swim bladder is
normally a transparent to opaque, whitish coloured organ.
Any change in colour, thickening of its wall, haemorrhage
or presence of fluid should be recorded. Evaluation of the
gonads provides information on the sex of the fish and degree
of maturation and a sample for histological assessment can be
performed slicing a section not thicker than 1 cm. Bouin’s
fixative has been recommended for this tissue as gonads in an
advanced stage of development can be hard to cut after
routine formalin fixation.
The kidney can be examined after the swim bladder has
been moved aside. Many infectious and non-infectious
conditions impact on the kidney and possible changes
include colour abnormalities, swelling, haemorrhage or a
granular appearance. Both the cranial and caudal areas
should be sampled for light microscopy avoiding
compressing the tissue by cutting first the peritoneal sheet
before attempting to lift the sample.
Maintaining an organised and systematic approach to the
necropsy is an important aspect of the procedure, and careful
observations made during this examination will provide
valuable information not only immediately, but consequently during the interpretation of the histological sections.
All tissues samples must be clearly identified with a reference code when sent for processing to ensure that there is no
risk of incorrect reporting.
Words of wisdom: ‘A poorly performed necropsy cannot be improved at a later stage’
3.3 Necropsy Procedure
31