FISHERY BULLETIN: VOL. 80, NO. 2 



should be 0.01-0.05 of the lethal concentrations. 

 Since a small rise in temperature or salinity can 

 shift the LC50 by one order of magnitude (Eisler 

 1972), most pesticides may be more harmful than 

 previously assumed. A synergistic effect of sev- 

 eral sublethal concentrations of pollutants is pos- 

 sible. They may exist in such low concentrations 

 that conventional analysis or collection methods 

 will not detect them, especially herbicidal con- 

 taminants. However, Seba and Corcoran (1969) 

 found that surface slicks formed by a film of or- 

 ganic matter concentrated pesticides in south- 

 west Biscayne Bay to detectable levels, up to 137 

 times as much as slicks in the Florida Current. 



Although the reaction of gill tissue to toxic 

 chemicals appears to be nonspecific in regard to 

 the particular chemicals present, and it is there- 

 fore difficult to indict any one particular com- 

 ponent or group of components in nature, the 

 overall result of gill damage is impairment of 

 function. Regardless of cause, pathological 

 changes reduce the useful respiratory surface 

 and make gas exchange difficult, which stresses 

 the fish and eventually weakens it. 



Disease has been known to change behavior in 

 fish (National Academy of Sciences 1973) and in- 

 fluence their chance for survival. Impaired func- 

 tion of an organ and reduced efficiency require 

 expenditure of energy which cannot be used for 

 other life processes such as feeding, reproduc- 

 tion, and predator avoidance. In case of gill dam- 

 age, metabolic activity must be reduced to a 

 minimum in order to reduce oxygen demand 

 (Wedemeyer et al. 1976), and the fish become 

 weakened and stressed. Selye's (1950) definition 

 of stress was used in reference to fish by Wede- 

 meyer (1970): "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." Unfortunately, 

 some of the metabolic changes may also contrib- 

 ute to increased susceptibility to disease (Wede- 

 meyer et al. 1976). 



When fish are weakened by environmental fac- 

 tors, chemicals, or poor nutrition, their resist- 

 ance to infestation and infection by Monogenea, 

 Trichodina, and bacteria is reduced (Schaper- 

 claus 1954; Wedemeyer et al. 1976). These facts 

 are well known to the aquaculture and aquarium 

 industries. Most research on immune reactions is 

 done in human and veterinary medicine, but 

 parallels can be drawn since fishes' immune sys- 

 tems, although less advanced, resemble those of 

 other vertebrates (Sindermann 1970). Mucus 



antibody may be active against some external in- 

 festations (Anderson 1974); thus, a parasite must 

 be able to avoid the immune reaction of the host 

 (Williams 1970). Stress-provoked physiological 

 changes may cause a disturbance of the host's im- 

 mune system, and damaged or irritated gills can 

 then become heavily infested with parasites. 

 Snieszko (1974) shared the belief of other scien- 

 tists that the aggravating effect of stress from 

 various types of pollution caused a high inci- 

 dence of infectious disease in fishes, and men- 

 tioned that this belief, unfortunately, was not yet 

 adequately documented. Sindermann (1979) 

 summarized some of the recent supporting evi- 

 dence that toxins have a deleterious effect on the 

 immune response of fishes. This study of Bis- 

 cayne Bay fishes suggests that, in the presence of 

 sublethal quantities of pollutants in a natural 

 marine environment, fish suffered from gill 

 damage which produced stress, physiological 

 and physical compensation, leading to weaken- 

 ing, reduced immunity, and heavy parasitic in- 

 festation. 



ACKNOWLEDGMENTS 



I thank Edwin S. Iversen, Eugene F. Corcoran, 

 and Donald P. de Sylva of the Rosenstiel School 

 of Marine and Atmospheric Science, University 

 of Miami; and George T. Hensley and Lanny R. 

 Udey of the School of Medicine, University of 

 Miami, for their advice and assistance during 

 this study. 



Special thanks go to James T. Tilmant, Bis- 

 cayne National Monument; James F. Redford, 

 Jr., Dade County Commissioner; Henry J. 

 Schmitz and Edward Gancher, Dade County De- 

 partment of Environmental Resources Manage- 

 ment; Robert L. Taylor, South Florida Water 

 Management District; and Keith Dekle, Florida 

 Power and Light Company, for help with field 

 work and obtaining water quality data. 



I am grateful to Fay Mucha, Rosenstiel School 

 of Marine and Atmospheric Science, University 

 of Miami; and Elaine Kraus, Medical School, 

 University of Miami, for assistance with histo- 

 logical work and photomicrography. 



Funds were provided by the Rosenstiel Fund, 

 University of Miami, RSMAS. The Richard G. 

 Bader Memorial Student Fund supplied a gill 

 net and photographic material. This is a contri- 

 bution from the Rosenstiel School of Marine and 

 Atmospheric Science, University of Miami, 4600 

 Rickenbacker Causeway, Miami, FL 33149. 



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