SINDERMANN: INTERNAL DEFENSES OF CRUSTACEA 



perature for American lobsters) . It is important 

 to note (in view of the very low seasonal tem- 

 peratures of waters in which lobsters live na- 

 turally) that at 1° C the pathogens i^ersisted 

 in the host in low numbers but with virulence 

 unchang-ed, and they produced mortalities when 

 the temperature increased. Experimentally in- 

 fected lobsters were also sensitive to and died 

 from rapid increases or decreases in environ- 

 mental temperatures — although the temperature 

 changes used in the experiments were probably 

 greater than those that would normally be ex- 

 perienced in nature. 



Findings in vivo were paralleled by in vitro 

 results of growth of Gaffkya in lobster serum — 

 with a more I'apid increase to a peak of bac- 

 terial numbers with increasing temperature. 

 The organism grew in culture at all the exper- 

 imental tem])eratures (within a range of 1° to 

 20° C) ; at 1° C the bacterial growth curve was 

 erratic — it decreased in numbers to the 30th day, 

 then a log increase progressed to the 60th day, 

 followed by a substantial decline. The impor- 

 tant observation, of course, is that G. homari can 

 survive within the range of environmental tem- 

 peratures experienced by American lobsters and 

 that the pathogen causes mortality more rapidly 

 as temperature increases. 



A concurrent physiological and biochemical 

 study by Stewart, Arie, Zwicker, and Dingle 

 (1969) and Stewart, Foley, and Ackman (1969) , 

 in which an attempt was made to define features 

 of the infection that lead to death of lobsters, 

 produced several interesting results. The path- 

 ogen lacked proteolytic, lipolytic, and fibrinolytic 

 exoenzymes, suggesting that harmful effects are 

 not caused by direct destruction of tissue. The 

 authors observed that although in vitro growth 

 of G. homari was limited by the carbohydrate 

 level of the lobster serum medium used, pre- 

 sumably such a level would be maintained in 

 vivo at the exiiense of other tissues. Drastic 

 reductions in hepatopancreatic glycogen and 

 hemolymph nonprotein nitrogen characterized 

 later stages of the infection. No evidence of a 

 toxin was detected, and the conclusion was that 

 gafTkaemia is largely a wasting type of disease 

 — that death from the disease was "a result of 

 an unsuccessful competition on the part of the 



lobster for its own readily available storage ma- 

 terial." 



On the basis of experimental inoculations and 

 subsequent mortalities. Bell and Hoskins (1966) 

 suggested that Gaffkya might be pathogenic for 

 the Dungeness crab, Cancer magister, and the 

 shrimp Panda Ins platyceros from the Pacific 

 coast. That observation could be important in 

 view of recent introductions of American lob- 

 sters (some possibly carrying Gaffkya) on the 

 Canadian west coast. Other ex])erimenta! 

 studies (Cornick and Stewart, 1968b) indicated 

 that the bacterium may also be pathogenic for 

 east coast crabs (Cancer irroratus, C. borealis, 

 and Hyas coarctatus) . In vitro growth of the 

 ]iathogen in crab sera was similar to that in 

 lobster serum, suggesting susceptibility of the 

 crabs. However, agglutinins for G. homari, 

 which were demonstrated in the sera of one of 

 the crab species (C irroratus) , might counteract 

 the favorable bacterial growth in vivo and reduce 

 the severity of infections in the crab. Cornick 

 and Stewart extended their observations by inoc- 

 ulations of C. irroratus with suspensions of G. 

 homari. After 49 days the surviving crabs 

 (three) were found to be heavily infected (10^ 

 organisms/ml hemolymph). Passage through 

 the crabs did not alter pathogenicity of Gaffkya 

 to lobsters. A repetition of the crab inoculations 

 with larger numbers of crabs provided some evi- 

 dence of greater mortalities in experimental 

 groups than in controls. Pathogenicity for rock 

 crabs was less than for lobsters, as indicated by 

 a mean time to death of 42 days in crabs, against 

 only 18 days in lobsters. The authors mentioned 

 the possible role of rock crabs as reservoirs of 

 infection for lobsters, in view of reduced path- 

 ogenicity and prolonged mean time to death in 

 crabs. 



From the foregoing, it is apparent that ex- 

 perimental studies with G. homari have been nu- 

 merous and vai'ied and have provided significant 

 insights aljout the internal defenses of Crusta- 

 cea. Important areas for future study include 

 determination of whether strains of the pathogen 

 with different virulences exist, and determina- 

 tion of whether virulence may be increased by 

 rapid passage through impounded lobster pop- 

 ulations. 



475 



