521 
Daily growth increments in otoliths of 
juvenile weakfish, Cynoscion regalis: 
experimental assessment of changes 
in increment width with changes 
in feeding rate, growth rate, 
and condition factor 
Richard Paperno 
University of Delaware 
Graduate College of Marine Studies, Lewes, Delaware 1 9958 
Present address: Florida Department of Environmental Protection 
Florida Marine Research Institute 
1220 Prospect St., Suite 285, Melbourne, Florida 32901 
E-mail address: rpaperno@winnie.fit.edu 
Timothy E. Targett 
University of Delaware 
Graduate College of Marine Studies, Lewes, Delaware 1 9958 
Paul A. Grecay 
University of Delaware 
Graduate College of Marine Studies, Lewes, Delaware 1 9958 
Present address: Department of Biological Sciences 
Salisbury State University, Salisbury, Maryland 21801 
Abstract .—Laboratory analyses 
were conducted on age-0 weakfish, 
Cynoscion regalis , to determine if depo- 
sition rate of otolith increments was 
daily and to examine the relation 
among otolith increment growth, daily 
feeding rate, specific growth rate, and 
condition factor. Tetracycline-marked 
juveniles (n= 58) had a mean deposition 
rate of 0.98 (0.03 SE) increments/d. 
Feeding rate significantly affected in- 
crement width and was positively cor- 
related with somatic growth rate and 
condition factor. Increment width re- 
sponse to changes in ration level was 
immediate, significant differences oc- 
curring between day 7 and 14. Mean 
increment width and specific growth 
rate were positively correlated (r=0.86). 
The continuation of otolith growth dur- 
ing periods of negative fish growth re- 
flects the conservative nature of otolith 
growth and the lack of otolith resorp- 
tion. An established relation between 
known growth rates of juvenile weak- 
fish in the laboratory and otolith incre- 
ment width will allow otolith increment 
widths to be applied to field samples. 
Such analyses could be used to exam- 
ine closely factors affecting growth, 
survival, and recruitment. 
Manuscript accepted 27 February 1997 
Fishery Bulletin 95:521-529 ( 1997). 
Growth rates in fishes can be deter- 
mined by using scales, otoliths, 
modal analysis, RNA-DNA ratios, 
and assorted skeletal structures 
(Bagenal, 1978; Campana and 
Neilson, 1985; Summerfelt and 
Hall, 1987). Interpretations from 
these structures are based upon 
assumptions that increments within 
otoliths are added periodically and 
that the change in thickness of con- 
secutive rings is proportional to fish 
length (Campana and Neilson, 
1985). Otoliths have also proven to 
provide an accurate record of fish 
growth because there has been no 
evidence of resorption (Degens et ah, 
1969; Dunkelberger et al., 1980; 
Watabe et ah, 1982; Mugiya, 1987), 
except under extreme physiological 
stress (Mugiya and Uchimura, 1989). 
The periodicity of increment ad- 
dition has been shown to be daily 
in larval and juvenile fishes (Cam- 
pana and Neilson, 1982; Hettler, 
1984; Schmitt, 1984; Tsukamoto, 
1985; Wilson et al., 1987; Tzeng and 
Yu, 1989; Monaghan, 1993). Otolith 
microstructure has more recently 
been used to compare growth of dif- 
ferent cohorts within a year class 
(Townsend and Graham, 1981; 
Warlen, 1982; Methot, 1983; Jones, 
1985), examine life history transi- 
tions (Brothers and McFarland, 
1981; Laroche et ah, 1982; Powell, 
1982; Miller and Storck, 1982; Vic- 
tor, 1986; Thresher and Brothers, 
1989), estimate mortality and sur- 
vival (Crecco et ah, 1983; Graham 
and Townsend, 1985; Neilson and 
Geen, 1986; Essig and Cole, 1986; 
Dalzell et ah, 1987; Post and Pranke- 
vicius, 1987; Rice et ah, 1987), and 
determine the effects of biotic and 
abiotic factors on microstructure 
