FISHERY BULLETIN: VOL. 76. NO 4 



Snieszko ( 1962) stated, concerningA. liquefacicns 

 that ". . . fish may have latent infections that 

 flare up when the flsh are exposed to stress." 



There are recent published accounts of two viral 

 diseases of marine invertebrates which also indi- 

 cate that latent infections may be provoked into 

 patency by environmental stress. One, a 

 Baculovirus infection of pink shrimp, Pcnaeus 

 duororum, was first recognized in stressed 

 laboratory populations (Couch 1974b, 1976). The 

 other, a herpes-like viral infection of oysters, was 

 discovered in a population held in a heated power 

 plant effluent in Maine (Farley et al. 1972). 



An association of shrimp virus disease and low- 

 level chronic exposure to pollutant chemicals is 

 being explored at the Gulf Breeze Environmental 

 Research Laboratory of the U.S. Environmental 

 Protection Agency (Couch 1974a, 1978). In this 

 work a virus disease of pink shrimp caused by B. 

 penaei reached patent levels and caused mor- 

 talities of dO-SO'Vo in shrimp exposed to the PCB 

 Aroclor 1254 and to the organochlorine insecticide 

 Mirex (Couch and Nimmo 1974a, b; Couch 1974a, 

 b, 1976). Other experiments in which the shrimp 

 were crowded, but not exposed to chemicals, re- 

 sulted in similar enhancement of virus infections, 

 indicating that environmental stress may be an 

 important determinant of patent infections. The 

 virus infection has been found subsequently in 

 brown and white shrimp (Overstreet and Howse 

 1977; Couch 1978). 



Couch and Courtney (1977) have recently pro- 

 posed an elaborate and unique conceptual scheme 

 to utilize the shrimp virus for interactive bioas- 

 says for chronic sublethal effects of contaminants. 

 The authors point out that there are a number of 

 possible interactions of host, pathogen, and chem- 

 ical stressors — change in resistance of shrimp to 

 the virus, enhancement of widespread latent in- 

 fections in the shrimp population, change in viru- 

 lence of the virus, and losses of diseased shrimps 

 by cannibalism. Criteria developed by Couch and 

 Courtney for interaction include increased viral 

 prevalence in stressed populations (as indicated 

 by numbers of inclusion bodies), increased infec- 

 tion intensity in stressed individuals, increased 

 mortality in stressed populations, and greater 

 cytopathic effects in infected and stressed indi- 

 viduals. The shrimp virus infection has great po- 

 tential for elucidating effects of pollutants on 

 host-pathogen relationships. 



An association of high environmental tempera- 



tures with high disease prevalence (or disease en- 

 hancement) in molluscan shellfish sampled from 

 thermal effluents has been made recently. Farley 

 et al. (1972) described a lethal herpes-type virus 

 disease of oysters held in heated discharge water 

 in Maine. The disease, which apparently existed 

 at a low enzootic level in oysters growing at nor- 

 mal low environmental temperatures (12°-18°C 

 summer temperatures), seemed to proliferate in 

 oysters maintained at elevated temperatures 

 (28°-30°C) and to produce mortalities in those 

 populations. Intranuclear inclusion bodies, con- 

 taining viral particles, characterized advanced in- 

 fections. Mortalities of oysters held at higher 

 temperatures were correlated with greater preva- 

 lence of the viral inclusions. Elevated water tem- 

 peratures were considered by the authors to favor 

 spread of the infection or to activate latent infec- 

 tions, or both. 



This evidence for a possible role of environmen- 

 tal stress in activating latent viral infections could 

 hardly be termed overwhelming, since it is possi- 

 ble that new infections produce the effects discus- 

 sed. However, the two viral diseases may provide 

 an insight into the total effect of pollutant and 

 other environmental factors on disease prevalence 

 and disease-caused mortalities. The carrier state 

 is often difficult to diagnose, but it may play a 

 much larger role in the epizootiology of marine 

 disease than can be demonstrated at present. 



ENVIRONMENTALLY INDUCED 

 ABNORMALITIES 



Neoplasms (Tumors) 



The terms "neoplasia" and "neoplasms," par- 

 ticularly as they concern lower animals, are 

 difficult to define precisely. The Oxford Dictionary 

 definition of neoplasm is "a new formation in some 

 part of the body; a tumor." More elaborate defini- 

 tions exist. Warren and Meissner (1971) defined a 

 neoplasm as "a disturbance of growth charac- 

 terized primarily by an unceasing, abnormal, and 

 excessive proliferation of cells." Prehn (1971) 

 defined neoplasia as "that form of hyperplasia 

 which is caused, at least in part, by an intrinsi- 

 cally heritable abnormality in the involved cells." 

 Although neoplasia has been studied most exten- 

 sively in humans and laboratory mammals, the 

 existence of tumors in fish and shellfish has been 

 recognized for almost a century (the first oyster 

 tumor, for example, was reported by Ryder in 



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