SINDKRMANN: fOLLl'TION-ASSOCIATKl) OISEASKS AND ABNOKMAI.ITIKS 



maximum observed environmental levels; 2) usu- 

 ally single chemicals are tested, ignoring possible 

 synergisms and antagonisms; 3) tests are often 

 static acute rather than chronic exposures in 

 flow-through systems; and 4) experimental ani- 

 mals are often under stress from the mere act of 

 confinement. 



These and other limitations of experimental 

 studies degrade the evidence obtained to cir- 

 cumstantial when attempts are made to extrapo- 

 late findings to natural populations in polluted 

 habitats. Despite this handicap, there is a large 

 and useful literature on experimental lesions in 

 fish and shellfish produced by chemicals which 

 occur as contaminants in the coastal environment. 



The presence of specific pollutants cannot be 

 recognized by the occurrence of specific lesions, 

 but a general description of pathological responses 

 can be useful. Categories of pathological responses 

 which should be considered in experimental 

 studies are; 1 (inflammation (acute and chronic); 

 2) degeneration (including edema, necrosis, and 

 metaplasia); 3 ) repair and regeneration (prolifera- 

 tion, hyperplasia, and scar formation); 4) neo- 

 plasia (including consideration of cell origin, 

 stage, and type — whether benign or malignant); 

 and 5) genetic derangement (including 

 chromosomal changes and skeletal abnor- 

 malities). 



CONTAMINANT EFFECTS ON 

 RESISTANCE AND IMMUNE RESPONSES 



Suppression of immune responses by toxicants 

 such as heavy metals and pesticides has been 

 demonstrated repeatedly in mammals (Kolom- 

 iitseva et al. 1969; Hemphill et al. 1971; Khan and 

 Hill 1971; Jones et al. 1971; Roller 1973; Street 

 and Sharma 1975). Therefore, it might be expected 

 that environmental pollutants could influence the 

 ability of fish and shellfish to resist infection by 

 reducing the effectiveness of external and internal 

 defense mechanisms, and indeed there is some 

 evidence that this is so. Changes in the principal 

 external defenses — mucus secretion offish and the 

 epicuticle of Crustacea — have already been men- 

 tioned in connection with fin erosion and exo- 

 skeletal erosion. Some specific information is 

 available about contaminant influences on inter- 

 nal defenses, principally through suppression of 

 immune responses. Environmental stress from 

 contaminants can affect internal resistance to in- 

 fection in fish by causing a decrease in phagocytic 



activity (Wedemeyer 1970) or a decrease in anti- 

 body synthesis (Goncharov and Mikyakov 1971). 

 Both mechanisms have been demonstrated ex- 

 perimentally. 



One of the best pieces of supporting infor- 

 mation about suppression of host responses was 

 derived from a recent multidisciplinary experi- 

 mental study of the effects of short-term sublethal 

 exposures to cadmium on the teleost Tautogolab- 

 rus adspefsus (Calabrese et al. 1974). The study 

 included chemical analyses of tissue uptake, 

 physiological and biochemical effects, his- 

 topathological changes, and effects on the immune 

 system. Robohm and Nitkowski ( 1974), who were 

 responsible for the immunology, found that expo- 

 sure offish to 12 ppm cadmium affected phagocyte 

 response to foreign antigen, but not the humoral 

 response. The rate of bacterial uptake in phago- 

 cytes of liver and spleen was increased, but the 

 rate of bacterial destruction within the phagocytes 

 was decreased significantly. No change was ob- 

 served in the antibody response of immunized con- 

 trol and experimental fish as determined by 

 hemagglutination techniques. The authors postu- 

 lated that cadmium may prevent delivery of 

 lysosomal substances to the phagocytic vacuole, or 

 may inhibit the action of these substances on bac- 

 teria, but that cadmium does not seem to inhibit 

 antibody synthesis by lymphocytic cells. The au- 

 thors further suggested that cadmium and possi- 

 bly other pollutants may affect fish populations by 

 causing phagocytic dysfunction, reducing the re- 

 sistance offish to facultative and other pathogens. 



The effect of sublethal copper exposure on the 

 immume response of juvenile coho salmon, On- 

 corhynchus kisutch, was examined by Stevens.'^ 

 At copper levels of 18 )U,g/l, agglutinin titers in 

 fingerlings injected intraperitoneally with Vibrio 

 anguillarum bacterin were significantly lower 

 than those of controls. Copper exposure also re- 

 duced survival of coho salmon fingerlings during 

 saltwater acclimation. 



Reduction in immunological competence may 

 well have been involved in observed outbreaks of 

 vibrosis (V . anguillarum ) in eels exposed to copper 

 (R0dsaether et al. 1977) and in epizootics of 

 Aeromonas liquefaciens (= A. hydrophila) in 

 salmon and suckers exposed to copper and zinc 

 pollution (Pippy and Hare 1969), although in 



'^Stevens, D. G. 1977. Survival and immune response of 

 coho salmon exposed to copper. Environ. Prot. Agency - 600/3- 

 77-031, 37 p. 



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