A rapid staining procedure for detection of recent skin and fin
injuries was tested in juvenile Chinook salmon Oncorhynchus tshawytscha. Immersion of anesthetized fish for 1 min in aerated aqueous solutions of the synthetic food
dye fast green FCF (
Food Green 3) at concentrations of 0.1 to 0.5% produced consistent and visible staining of integumental
injuries. A 0.1%
fast green concentration was satisfactory for visual evaluation of
injuries, whereas a 0.5% concentration was preferable for digital photography. A rinsing procedure comprised of two 30 s rinses in fresh water was most effective for removal of excess
stain after exposure of fish. Survival studies in fresh water and seawater and histopathological analyses indicated that short exposures to aqueous solutions of
fast green were non-toxic to juvenile Chinook salmon. In comparisons of the gross and microscopic appearance of fish exposed to
fast green at various times after injury, the
dye was observed only in areas of the body where epidermal disruption was present as determined by scanning electron microscopy. No
dye was observed in areas where epidermal integrity had been restored. Further comparisons showed that
fast green exposure produced more consistent and intense staining of skin injury sites than a previously published procedure using
trypan blue. Because of its relatively low cost, ease of use and the rapid and specific staining of integumental
injuries,
fast green may find widespread application in fish health and surface injury evaluations.