Note:  This procedure should only be performed by fish health professionals.   If the fish is alive and is not to be euthanatized, sedation with MS-222 (Finquel) reduces stress upon the fish and makes sample collection easier. The fish is placed in a small amount of water and a small quantity of  MS-222 is added (to effect). Once the fish rolls laterally, sedation is deep enough for sample collection. To recover the fish, place it in a large quantity of fresh water. The exposure to the MS-222 may make the fish defecate, providing a fecal sample for smears.

            To euthanatize a fish, an overdose of MS-222 (>150 mg/L) is used. Once the operculum have stopped moving, the necropsy procedure can be initiated and  samples can be collected. 

Skin Scraping

             If the fish is to be revived, the skin scrapes should be gentle and limited in size. Scrape a small area of the body in a cranial to caudal direction using a glass microscope slide. The scrape should contain mucus with a few scales. If the fish is dead, deeper and larger scrapes can be obtained. The best place to collect scrapes from dead fish is ventral to and between the pectoral fins. The fins provide some protection of the underlying skin from mechanical damage and drying. Once the mucus and scales are collected on the end of a slide, it is smeared along a second slides (similar to a blood smear). The sample should be examined before it dries at low magnification and at 200 X. Particular attention should be given to any movement within the mucus for the detection of  exoparasites.  Colonies of bacteria (ex: Cytophagia columnaris) and fungal hyphae (ex: saprolegniosis) may be observed in skin scrapes, if present. The edges of erosions or ulcers (if present) should also be scraped and examined for pathogens.

 Fin Clipping 

Spread the tail fin apart of the sedated or dead fish. Take a small pair of scissors and trim a wedged shaped area between the fin rays. Place the wedge on a glass slide, add a drop of water to the fin wedge, and then cover with a coverslip. The drop of water and coverslip will keep the sample moist and allow the sample to spread out, thus making a proper cytologic preparation.  The presence of gas bubbles within the fin tissue is indicative of ‘gas bubble’ disease (supersaturation of the water by gas).

 Gill Clipping 

            If the fish is to be revived, extreme care must be taken in obtaining gill samples.  Severely affected sick fish may die following gill collection from a biopsy procedure. Only a small sample of gill tissue is needed.  Carefully lift the operculum (gill cover) and using a small pair of scissors remove a small section of gill filaments. If the cut is superficial, bleeding will be minimal. Do not cut the gill arch since they contain several large vessels and massive fatal hemorrhage will result if they are transected.  Once the gill filaments are cut,  carefully transfer them to a glass slide. Place one drop of water over the gill filaments and  cover with a coverslip. If done correctly, the filaments will spread out on the glass slide and form a single layer which will be partially transparent.  If the fish is dead, take a larger section of the gill filaments but, again, do not include the gill arch.  Large red dilated secondary filaments represent telangiectasis and occur as a post mortem artifact due to the changes in osmotic pressures (water versus air). The gill filaments should be evaluated at low magnification as well as 200X.