ceding year suffered high mortalities after 

 insertion of pearl cores, and high percentages 

 of pearls produced by infected individuals were 

 of low quality (Sakaguchi, 1964). 



DISEASES OF CRUSTACEA 



Crustacea such as crabs, lobsters, and 

 shrimps are among the most valuable of ma- 

 rine crops in many parts of the world. Large 

 populations of crustaceans occur on the con- 

 tinental shelves, and often part or all of the 

 life cycle is spent in estuarine or inshore 

 waters. Here individuals may be observed and 

 studied in natural habitats as well as in the 

 landed catches. These studies have disclosed 

 certain parasites and diseased conditions. Dis- 

 ease may have severe effects on survival, 

 particularly when crabs and lobsters arc im- 

 pounded before sale. Diseases e.xist in natural 

 populations of Crustacea as well, although ef- 

 fects are less apparent than in captives or in 

 more sedentary marine animals. No widespread 

 epizootic is known for marine Crustacea that 

 would be comparable to "krebspest," a fungus 

 disea.se that swept through populations of fresh- 

 water crayfishes of Europe (Schikora, 1906, 

 1926; Schjiperclaus, 1935; Nybelin, 19.35; 

 Mannsfield, 1942). 



CRABS 



Many species of crabs have great commercial 

 value in various parts of the world. Con.se- 

 quently, diseases and parasites have been in- 

 cluded in studies of factors which affect 

 abundance. Microbial diseases, helminths, and 

 parasitic crustaceans occur in crabs. 



Microbial Diseases 



Among the microbial diseases of crabs are 

 those caused by a virus, several fungi, bacteria, 

 and a variety of protozoans. 



Viruses. — Virus diseases have not been re- 

 ported from marine invertebrates, with the e.x- 

 ception of one described recently, and only very 

 briefly, by Vago (1966), in swimming crabs, 

 Portunus depmator (L.), from the French 

 Mediterranean coast. Gross disea.se signs in- 

 cluded the slow development of paralysis, and 

 sometimes a slight darkening (presumably of 

 the exoskeleton) in later pha.ses of the disea.se. 

 Virus particles were seen with the electron 



microscope; inoculation of blood fi'om infected 

 animals produced disease signs in healthy 

 crabs ; and infections were obtained with ultra- 

 filtrates and ultracentrifugates of homogenized 

 tissues from sick crabs. No indication of disease 

 prevalence was given by Vago. 



Recently, Sprague and Beckett (1966) have 

 published a preliminary note on a di.scase of 

 soft-shell and molting blue crabs, Calliiiectes 

 sapixhis Rathbun. The disease, of undetermined 

 but possibly viral etiology, was called "gray 

 crab di.sease." It occurred in crabs from seaside 

 b.iys of Virginia, where it apparently caused 

 some deaths among captive crabs. 



Bucteria. — King crabs, Paraiithodcs camt- 

 schutica (Tilesius) and P. platypus Brandt, 

 from the eastern North Pacific are occasionally 

 aU'ected by "rust disease," which .seems to result 

 from action of chitin-destroying bacteria on 

 the e.xoskeleton. Microorganisms of this type 

 are common in the sea (ZoBell and Rittenberg, 

 1938; Hock, 1940, 1941) but usually degrade 

 the exoskeletons of dead animals and do not 

 affect living individuals. Over thirty species of 

 chitin-destroying bacteria are known, of which 

 half have been isolated from shells of 

 crustaceans. 



Bright, Durham, and Knud-sen ' described 

 ob.servations of rust disease in landed catches 

 of king crabs from Kachemak Bay, Cook Inlet, 

 Alaska, as well as experimental studies of the 

 bacteria involved. The disease was character- 

 ized by progressive darkening and softening of 

 the exoskeleton, particularly on the ventral sur- 

 faces. Underlying living tissues were unaf- 

 fected. Natural infections reached 11 percent 

 in larger older crabs in 1957 but were much 

 lower in 1958 and 1959. Shell abrasions and 

 injuries .served as foci of the di.sea.se, which 

 developed experimentally within 2 weeks. The 

 disease was not carried over to the new exo- 

 skeleton after molting, but recently .shed crabs 

 were highly susceptible because the new shell 

 was easily punctured or abraded. Chitin-de- 

 strojing bacteria were isolated from infected 



■' Data furnished from unpublished contract report. "Kin^r crab 

 investiKations of Cook Inlet, Alaska," by Donald B. Bright, Floyd 

 E. Durham, and Jens W. Knudsen of the Allan Hancock Founda- 

 tion. University of Southern California. Los Angeles, to BCF 

 Biological Laboratory, Auke Bay, Alaska, June I'JSO. (Cited with 

 permission of Laboratory Director, BCF Biological Laboratory, 

 Auke Bay. Alaska.) 



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U.S. FISH AND WILDLIFE SERVICE 



