When submitting a live fish sample what is it important to consider
- Transport conditions - heat O2
- Allow 2L of water per 5-10 small fish
- Fill bags 1/4 full of water, leaving the remainder filled with air or oxygen
- Seal and place in second bag along with ice
- Place and seal in outer container - amount and layers of packing depend on the situation
- If you doubt that fish will arrive alive, select samples for individual tests, especially fixed material and smears and perhaps cultures of lesions
When submitting freshly dead samples what is it important to consider
- Submit freshly dead fish sealed in plastic bags, preferably individually wrapped and on ice
- Ensure the fish are not in direct contact with ice or water
- Anaesthetic overdose may cause some parasites to leave the fish so it is recommended smears for parasites be made as soon as possible
- For organic chemical analysis, percussion stunning with a sharp blow to the head is suitable unless the brain is needed for analysis
- Blunt force will also induce haemorrhage artefacts in the gills which may not be wanted
Australia post accepts biological substances under what conditions
- Australian addressee much be recognised by the lab
- The sender must
Qualified medical practitioner
Qualified vet surgeon
Public hospital, clinic or lab
A member of a commonwealth, state or territory police force - Triple packaging
How to set fish for histopathology
Formalin fixation - finfish are the same isotonicity as higher vertebrates, so standard vertebrates fixatives are suitable
What are the exceptions of histopathology
- Rapid penetration is required
- Tissue that tend to separate during processing
- Fixation of small parasites that would otherwise wash off epithelial surfaces during processing
What is Bouin’s fixative
Suitable for small specimens, especially very small fish that can be fixed and sectioned whole
What is Bouin’s fixative useful for
Skin and eyes, although eyes may be better fixed in neutral buffered formula after making a small slice in the back of the retina to aid penetration, as Bouin’s fixative may result in artefacts
What is Davidson’s fixative recommended for
Gils with suspected parasites
Within one week what must the tissue be trandered into from the Davidson’s fixative
70% ethanol within a week
External examination what to look at
- Corneal opacity may assessing the time of death
- (bi or uni) exophthalmia and/or hyphen is common finding with septicaemia but may also indicate gas disturbances
- open mouth as a common finding in a group of dead fish is likely of indicate respiratory distress
How to perform an external examination
- Lift and remove an operculum an examine gills and mouth
- Note gill colour the extent of mucous cover, and any gill or mouth lesion and parasite
- Gill colour is also a guide to the level of post mortem change as well as an indication of anaemia
- Focal lesions or increased mucus may indicate parasites or other irritants
What may parasitised fish show
Few gross signs, though surface parasites are common and often in sufficient numbers to be clinically significant
Where are protozoa and small flukes are best observed in
Wet smears
Where to prepare smears from
Gills and skin surfaces
For lab summations what must be done to the smears
air dried immediately
How are gills examined on microscope
Wet smear examination for microscopic external parasites
How to prepare wet smears of mucus from skin and gills
Lightly scrape the surface of the tissue with a scalpel blade, tranfer the mucus collected to a slide and dilute with a drop or two of water and place a cover slip o
What is important when doing wet smear
Use the same source of water for dilution as that of the fish
How to fix gills
Lift or cut the gill cover and fix one or more whole gill arches from small fish or at least 1.5 cm of an arch from larger fish
How to open the abdominal cavity
Using curved, blunt-ended scissors, open abdominal cavity along the mid-line to just in front of the vent (cut 1) and reflect dorsally (cut 2) or remove one abdominal wall (cut 2 and cut 3) to expose abdominal organs
For small fish, abdominal exposure is best made by one curved incision from in front of the anus curving towards the spine but remaining ventral to the kidney and extending forward to the gill arch (cut 2 and 3)
The abdominal flap can then be retracted ventrally to provide a sterile surface for handling tissues
What to look for in the abdominal cavity
Major organs and note size, colour, friability, haemorrhages, nodules, necrosis or parasites present in the organ
What is a good indicator of conditions
Level of abdominal or pancreatic fat
What may the presence of fluid in the abdominal cavity or swim bladder and/or serial congestion or petechiae indicate
Viral or bacterial diseases
What is the spleen
Major haematopoietic, lymphoid and phagocytic organ
