Sometimes, it is not always possible to make a diagnosis clinically and so, lab testing may be required.
To do this, fish will need to be freshly dead and the necropsy video I have placed on youtube will help you perform the necropsy.
The fixative I use is 10% neutral buffered formalin. If you are unable to obtain this, then less suitable alternatives include:
- formalin you use to treat fishes diluted 1:10 (i.e. 10% formalin solution),
- methylated spirits diluted 7:10 with water (i.e. 70% methanol solution),
- or household vinegar used neat.
The volume of fish tissues to fixative should be 1:10 for best results (but 1:5 is also acceptable). When sampling larger fish specimens, tissue sizes should be >1cm thick. Gills and intestines are the first to decompose and so these tissues need to be preserved in the fixative as soon as possible.
NB: Formalin is considered to be carcinogenic. Do not inhale or contact formalin. Wear suitable personal protective equipment.