ers. Some of these environmental factors are dras- 

 tic changes in temperature, lack of adequate food, 

 or overcrowding. Resistance of the host animal to 

 the disease is, of course, intimately related to 

 these stresses (Snieszko 1974). 



Environmental stresses have been implicated in 

 a number of fish and shellfish diseases, but are 

 difficult to quantify. Even a definition of stress can 

 be elusive. Selye ( 1950, 1952) defined stress as the 

 sum of all the physiological responses by which an 

 animal tries to maintain or reestablish a normal 

 metabolism in the face of a physical or chemical 

 force. Brett ( 1958) defined it as "A state produced 

 by any environmental or other factor which ex- 

 tends the adaptive responses of an animal beyond 

 the normal range, or which disturbs the normal 

 functioning to such an extent that, in either case, 

 the chances of survival are significantly reduced." 

 Another definition which identifies stress as the 

 product and not the cause of homeostatic change is 

 thatofEschetal. (1975): "Stress is the effect of any 

 force which tends to extend any homeostatic or 

 stabilizing process beyond its normal limit, at any 

 level of biological organization." 



Human activity has introduced or has increased 

 environmental stresses for fish in estuarine and 

 coastal waters. We have, for instance, added pes- 

 ticides and other synthetic chemicals which can, 

 even in low concentrations, drastically affect the 

 physiology of fish and shellfish, and with which 

 the species may have had no previous evolution- 

 ary experience. We have added heavy organic 

 loads, in the form of sewage sludge and effluents, 

 which can produce anaerobic or low-oxygen envi- 

 ronments and which are often accompanied by 

 other contaminants such as heavy metals, that 

 can interfere with enzymes of the fish and the food 

 organisms they consume. 



During the past decade, several diseases and 

 abnormalities offish and shellfish have been de- 

 scribed that seem associated with pollutant stres- 

 ses. These can be categorized and discussed as: 



1. Diseases caused by contaminant stress and 

 related pathogens; 



2. Stress-provoked latent infections; 



3. Environmentally induced abnormalities; 



4. Genetic abnormalities associated with 

 mutagenic and other properties of contam- 

 inants; 



5. Experimentally induced lesions; 



6. Contaminant effects on resistance and im- 

 mune response; and 



FISHERY BULLETIN: VOL. 76, NO. 4 



7. Pollutant-parasite interactions. 



In the first and second categories a synergistic 

 activity of chemical contaminants (or other form of 

 pollutant stress) and an infectious agent seems to 

 be a plausible explanation for at least some of the 

 observed effects. In categories three and four, it is 

 sometimes difficult to determine conclusively 

 whether environmental contaminants act directly 

 on target tissues or biochemical pathways, or if the 

 genetic material is first affected, with subsequent 

 changes in structure and/or function. 



During the past several years there have been 

 signs of increasing interest in relationships be- 

 tween marine fish and shellfish diseases and en- 

 vironmental pollution. Several conferences have 

 been held recently, including the 1974 Symposium 

 on Tumors in Aquatic Animals, held in Cork, Ire- 

 land; the 1975 Symposium on Sublethal Effects of 

 Pollution on Aquatic Organisms, held as part of 

 the 13th Pacific Science Congress in Vancouver, 

 B.C.; and the 1976 Conference on Aquatic Pollu- 

 tants and Biological Effects with Emphasis on 

 Neoplasia, held in New York. The amount of rel- 

 evant literature available for consideration 

 within the title "pollution-associated diseases and 

 abnormalities of fish and shellfish" is somewhat 

 overwhelming. Even the list of books containing 

 pertinent material is impressive (Dawe and 

 Harshbarger 1969; Snieszko 1970; Ruivo 1972; 

 Vernberg and Vernberg 1974; Koeman and Strik 

 1975; Ribelin and Migaki 1975; Dawe et al. 1976; 

 Lockwood 1976; Kraybill et al. 1977; Vernberg et 

 al. 1977). Additionally, significant recent reviews 

 have appeared, for example, Rosenthal and Alder- 

 dice (1976) and Mclntyre^. 



This paper attempts to summarize the present 

 state of knowledge about possible associations of 

 fish and shellfish diseases (infectious and nonin- 

 fectious) with estuarine and coastal pollution. 

 Much of the evidence for such associations is still 

 circumstantial and is presented as such. The orig- 

 inal literature on this subject, as for any 

 pollution-related subject, is voluminous. The ref- 

 erences cited here constitute only a small but, I 

 hope, a representative fraction of the published 

 information available. It should also be pointed 

 out here that this paper does not consider 



^Mclntyre, A. D. (Convenor). 1976. ICES working group on 

 pollution baseline and monitoring studies in the Oslo Commis- 

 sion and ICNAF areas. Report of the subgroup on the feasibility 

 of effects monitoring. Int. Counc. Explor. Sea, Doc. CM1976/ 

 E:44, 36 p. 



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