AbStraCt.-Developmental Insta- 

 bility (DI) has been proposed as an 

 inexpensive, quickly applied, and 

 sensitive indicator of stress that can 

 be utilized in early warning and in 

 monitoring anthropogenic impacts 

 on fish and other animals and 

 plants. A problem arises, however, 

 to the extent that natural stressors 

 confound the effects of human-in- 

 duced disturbances. Our objective in 

 this work was to investigate whether 

 a natural stressor, in the form of El 

 Nino conditions, contributed to DI 

 in the Pacific hake. Right-left 

 (fluctuating) asymmetry of otolith 

 length, width, growth rate, and 

 weight, as well as right-left otolith 

 shape differences, were used as mea- 

 sures of DI. Results show that in- 

 deed El Nino disrupts development, 

 indicating stress. This outcome sug- 

 gests that DI, as an early warning 

 and monitoring tool for stress, must 

 be used with caution. 



Developmental instability as 

 an indicator of environmental 

 stress in the Pacific hake 

 (Merluccius productus) 



Consuela L. Alados 

 Juan Escos 



Estacion Experimental de Zonas Andas 



Consejo Superior de Investigaciones Cientificas 



Almena. Spain 



Present Address: National Fisheries Research Laboratory 



U S Fish and Wildlife Service 



Naval Station Puget Sound. Seattle, WA 98 1 I 5 



John M. Emlen 



National Fisheries Research Laboratory 



U S Fish and Wildlife Service 



Naval Station Puget Sound, Seattle, WA 98 1 I 5 



Manuscript accepted 25 June 1993. 

 Fishery Bulletin 91:587-593 ( 1993). 



The viability of fish populations and 

 the ecological communities of which 

 they form a part is a matter of con- 

 cern to fisheries managers. At pres- 

 ent, awareness of ecological problems 

 often occurs only when stocks have 

 already begun to decline, when there 

 is clear evidence of disease or mor- 

 bidity, or when die-offs occur. 



Much work has been done on meth- 

 ods to assess adverse environmental 

 impacts on fish via physiological 

 stress measures (Adams, 1990a). 

 These methods can, in theory, be used 

 to monitor problems and, possibly, act 

 as early warning indicators. However, 

 most of these indicators either mea- 

 sure short-term acute stress response 

 (e.g., corticosteroid levels), or are ex- 

 pensive and laboratory-intensive. 

 They are cost-effective only in evalu- 

 ating already obvious signs that a 

 problem exists. In economically de- 

 pressed areas, including the devel- 

 oping nations, these methods are im- 

 practical. In addition, they generally 

 lack ecological relevance (Adams, 

 1990b). 



A possible alternative to these 

 methods lies in morphological mea- 



sures of developmental instability by 

 which changes (induced by environ- 

 mental or genetical stress) in the ba- 

 sic developmental strategy of organ- 

 isms can be assessed. For example, 

 chronic stress might aggravate right- 

 left asymmetry in normally bilater- 

 ally symmetric structures (Soule, 

 1967; Valentine and Soule, 1973; Val- 

 entine et al, 1973) or increase the 

 number of aberrations in circulus 

 patterns on scales (Shackell and 

 Doyle, 1990). Morphological measures 

 are inexpensive to obtain and cause 

 minimal or no damage to animals in- 

 volved. They can be quickly and in- 

 expensively applied not only in situ- 

 ations where concern has already 

 arisen, but also as standard moni- 

 toring tools. Screening of fry might 

 be valuable in assessing effectiveness 

 of various hatchery practices or in 

 evaluating smolt quality in Pacific 

 salmon. 



The efficacy of right-left, or "fluctu- 

 ating" asymmetry (FA) as an indica- 

 tor of both genetic and environmental 

 stress has been well documented. 

 Within populations, homozygosity 

 is associated with increased FA 



587 



