United States Environmental Protection Agency
Office of Research and Development, Atlantic Ecology Division
Narragansett, Rl
May 2000
Coastal 2000
Northeast Component
Fish Pathology Field Guide
Environmental Monitoring
and Assessment Program

Coastal 2000 Fish Pathology Field Guide
This docurrent was designed to be a brief field guide to the major types of pathological
conditions monitored by Coastal 2000 in the Northeast (lumps, growths, ulcers, fin erosion, gill
discoloration, and gill erosion). Included is a NMFS Technical Report that goes into
considerable more detail. Whenever a condition is encountered, the fish should be preserved
and sent to a qualified pathologist. Questionable conditions should be treated the same way.
The pathologist will make the final calls on all fish. When documenting a pathological condition,
the location should be recorded. Included in this document is a list of Coastal 2000 "location
codes" to be entered on the datasheet.
Figure 1. This is an example of an abnormal growth (above or penetrating the skin). This fish
has a large growth on its lower jaw.

Figure 2. This flounder has a lump (originating under the skin) visible on
its upper surface between its mouth and operculum, and its eye is
missing. The lump is raised and slightly discolored.
Figure 3. This is an example of lymphocystis which is caused by a virus.
Although lymphocystis can be found on the entire surface of the fish,
these small white and red growths are mostly on the fin cf this fish. These
would be considered lumps or growths.

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Figure 6. There are three lesions (ulcers) in different stages on this fish.
The most severe is the one on the caudal peduncle which penetrates down
to the muscle. The others are in front of the anal fin and show a loss of
scales and epithelium.
Figure 7. There appears to be a lesion (ulcer) above the pectoral fin of
this fish, but in actuality, because of the evenness and roundness of the
scar, is probably a bite from a lamprey.

Figure 8. This diagram highlights signs of fin erosion, including melanization of the
tissue adjoining the eroded area.
Figure 9. This caudal fin shows signs of erosion. Fin erosion would show
possible signs of damage to the fin rays including loss of tissue. Fins that are
split with no other sign of damage are probably torn, possibly from handling or
the net.

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Figure 10. This diagram highlights damage to fins and the body caused by physical processes
such as handling and trawling.
Figure 11. This very even cut on this fin shows little other sign of damage. This is
probably the result of a bite.

Figure 12. This is an example of gill discoloration. The operculum has
been removed to expose the gills. Typically, because the gills are a site of
gas exchange and they have a high blood flow, they are bright red. In this
fish, the lamellae are pale.
Figure 13. The operculum has been removed to show a portion of the gill
lamellae that have been eroded. The lamellae normally give the gills a
comb-like appearance. In this picture, some of the lamellae have been

Fish Pathology Location Codes
AD = Anterior Dorsal
AV = Anterior Ventral
PD = Posterior Dorsal
PV = Posterior Ventral
CD = Caudal Peduncle
AN = Anus
CR = Cranial
OP = Operculum
MO = Mouth
DF = Dorsal Fin
AF = Anal Fin
PLF = Pelvic Fin
PTF = Pectoral Fin
G = Gills
R = Right Side
L = Left Side
Combine R / L with code for a full description, e.g., RAD = Right Anterior Dorsal