FISHERY BULLETIN; VOL. 76. NO. 4 



Figure 4. — Ulcer with smooth margins in Atlantic herring, resulting from infection by the myxosporidan protozoan, Kudoa 



clupeidae. 



reasonable generalization that many of the infec- 

 tions that produce grossly visible ulcerations in 

 fish are bacterial, and are often due to pathogens of 

 the genera Vibrio, Pseudomonas, or Aeromonas 

 (Lamoletetal. 1976). Ulceration often begins with 

 scale loss or formation of small papules, followed 

 by sloughing of the skin, exposing the underlying 

 muscles, which may also be destroyed. Bacterial 

 ulcers may have rough or raised irregular mar- 

 gins, and will often be hemorrhagic. Ulcers may or 

 may not be associated with fin erosion. 



Shell Disease of Crustacea 



Also associated with badly degraded estuarine 

 and coastal waters is a disease condition in Crus- 

 tacea commonly referred to as "shell disease" or 

 "exoskeletal disease" or "shell erosion." This can 

 be considered in some ways as the invertebrate 

 counterpart of fin erosion. 



Homarus americanus and rock crabs (Cancer 

 irroratus ) from grossly polluted areas of the New 

 York Bight were found to be abnormal, with ap- 

 pendage and gill erosion a most common sign, by 

 Young and Pearce (1975). Skeletal erosion occur- 

 red principally on the tips of the walking legs, 

 ventral sides of chelipeds, exoskeletal spines, gill 

 lamellae, and around areas of exoskeletal articu- 

 lation where contaminated sediments could ac- 

 cumulate. Gills of crabs and lobsters sampled at 

 the dump sites were usually clogged with detritus, 

 possessed a dark brown coating, contained 



localized thickenings, and displayed areas of ero- 

 sion and necrosis. Similar disease signs were pro- 

 duced experimentally in animals held for 6 wk in 

 aquaria containing sediments from sewage sludge 

 or dredge spoil disposal sites. Initial discrete areas 

 of erosion became confluent, covering large areas 

 of the exoskeleton, and often parts of appendages 

 were lost. The chitinous covering of the gill fila- 

 ments was also eroded, and often the underlying 

 tissues became necrotic. 



Dead and moribund crabs and lobsters have 

 been reported on several occasions by divers in the 

 New York Bight Apex, and dissolved oxygen con- 

 centrations near the bottom during the summer 

 often approach zero (Pearce 1972; Young 1973). 

 Low oxygen stress, when combined with gill foul- 

 ing, erosion, and necrosis, could readily lead to 

 mortality. 



In a related study, Gopalan and Young (1975) 

 examined "shell disease" in the caridean shrimp, 

 Crangon septemspinosa, an estuarine and coastal 

 food chain organism common on the east coast of 

 North America and important in the diets of 

 bluefish, weakfish, flounders, sea bass, and other 

 economic species. Examinations of samples of 

 Crangon from the New York Bight disclosed high 

 prevalences (up to 15*7^ ) of eroded appendages and 

 blackened erosions of the exoskeleton. The disease 

 condition was only rarely observed at other col- 

 lecting sites (Beaufort, N.C., and Woods Hole, 

 Mass.). Histological examination of diseased 

 specimens produced findings similar to those of 



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