ASYMMETRY ANALYSIS IN FISHES: A POSSIBLE 

 STATISTICAL INDICATOR OF ENVIRONMENTAL STRESS 



David W. Valentine,' Michael E. Soule,^ and Paul Samollow^ 



ABSTRACT 



One of the more difficult tasks in evaluating the possible deleterious effects of multiple 

 toxicants on natural communities is in defining subtle sublethal effects before the onset 

 of chronic morbidity. We reason that before detectable changes in either species diversity 

 or species abundance occur subtle changes must take place in a number of important 

 processes, ranging from molecular to behavioral changes. Unfortunately, changes in these 

 parameters have proven most difficult to detect with current methodology. We, therefore, 

 have been examining the possible use of fluctuating asymmetry as a possible measure of 

 environmental stress. 



Fluctuating asymmetry is simply the random deviation from perfect symmetry of any 

 bilateral anatomical character. It is, therefore, a nonspecific measure of developmental 

 perturbation. 



Using asymmetry analysis on three species of marine teleost — barred sand bass, 

 Paralabrax nehulifer; grunion, Leiiresthes tenuis; and barred surfperch, Amphistichus 

 argenteus — from southern California and Baja California, we have been able to define 

 two possible asymmetry trends, historical and geographic. Asymmetry values are shown 

 to increase as we approach highly populated areas (southern California) both from the 

 north and south and also with time within southern California. Such increases in asym- 

 metry correlate well with the known distribution of various toxicants from this same area. 



Biological indices are urgently needed for 

 efficiently assessing the effects of man-induced 

 environmental stresses on the marine environ- 

 ment, a task w^idely acknowledged as both 

 important and difficult (National Scientific 

 Committee on Oceanography of the NAS-NRC 

 Ocean Affairs Board, 1971). Several general 

 approaches are now being used with mixed 

 results: 1) the documentation of die-offs or 

 sterility, such as results from anoxia, thermal 

 shock, pesticides, industrial wastes, oil spills, 

 etc., 2) the detection and description of anoma- 

 lies ascribable to microorganisms associated 

 with sewage, 3) the quantification of changes 

 in species diversity and community organiza- 

 tion, sometimes attributable to thermal, domes- 

 tic, or industrial effluents, and 4) population 

 changes in certain indicator species which 

 are themselves either resistant or sensitive 



' Department of Biology, University of California at 

 San Diego; present address: Dames & Moore, 1100 

 Glendon Avenue, Suite 1000, Los Angeles, CA 90024. 



^ Department of Biology, University of California at 

 San Diego, La Jolla, CA 92037. 



^Zoology Department, Oregon State University, Cor- 

 valHs, OR 97331. 



to specific pollutants (Wilber, 1969). Many of 

 the above methods have been criticized for 

 their insensitivity, lack of standardization, and 

 for being useful only after the occurrence of 

 significant biotic changes. The method we pro- 

 pose may be a useful and sensitive alternative 

 under certain conditions. 



Our approach is morphological and is based 

 on fluctuating asymmetry, the random signed 

 differences between the right and left sides of 

 a bilateral character (Van Valen, 1962). The 

 extent to which deviations from perfect sym- 

 metry occur is thought to be an estimate of 

 the regulatory capacity of the developmental 

 system in a particular environment. Our work- 

 ing hypothesis is that asymmetry will be in- 

 creased under certain kinds of environmental 

 stress due to the failure of homeostatic regula- 

 tory mechanisms. Such developmental effects 

 might occur before the concentration of toxi- 

 cants in waters or food reach levels high 

 enough to cause widespread morbidity. It 

 would be slightly easier to use variation per 

 se, such as estimated by the standard deviation 

 or coefficient of variation of a unilateral char- 



Manuscript accepted November 1972. 

 FISHERY BULLETIN: VOL. 71, NO. 2, 1973. 



357 



