Maillet and Checkley Effects of stawation on Brevoortia tyrannus 



163 



increments are formed daily in sagittae of Atlantic 

 menhaden larvae. A closely related species, the Gulf 

 menhaden 5. patronus, initiated increment deposition 

 at first feeding and formed an average of one growth 

 increment per day in sagittae (Warlen 1988). The fre- 

 quency of increment formation in juvenile Atlantic 

 menhaden held in enclosures also indicated that sagit- 

 tal growth increments are formed daily (Simoneaux 

 and Warlen 1987). 



Starvation of larval Atlantic menhaden for 1-3 days 

 did not result in the cessation of sagittal growth nor 

 systematically alter the periodicity of increment for- 

 mation from one increment per day. Larvae starved 

 for 2- and 3-days formed increments at rates similiar 

 to larvae which were fed continuously. Similiar results 

 have been reported for other species reared under 

 various feeding regimes, including starvation (Marshall 

 and Parker 1982, Campana 1983, Eckmann and Rey 

 1987). However, other studies investigating formation 

 of otoliths have found that periods of starvation may 

 affect the rate of increment formation (Townsend and 

 Graham 1981, Geffen 1982, McGurk 1984, 1987). 

 Growth increments formed during starvation and 

 periods of slow growth may be difficult to resolve due 

 to their small size , generally < 1 ^^m, which is near the 

 limit of resolution of most light microscopes. This may 

 have resulted in underestimation of the number of in- 

 crements in two of the experimental groups of Atlan- 

 tic menhaden larvae in our study and contributed to 

 the apparent nondaily deposition rate. Theoretical daily 

 increment width of larval Atlantic herring during early 

 growth (first 2 weeks) was predicted to be below the 

 limit of resolution of light microscopy (Campana et al. 

 1987). Examination of otoliths of fish exposed to sub- 

 optimal conditions indicated that age was underesti- 

 mated using light microscopy compared with high reso- 

 lution viewing by SEM (Jones and Brothers 1987, 

 Bailey and Stehr 1988). 



Microstructural growth patterns observed in sagittae 

 of larval Atlantic menhaden support the hypothesis 

 that variations in nutrition and environmental factors 

 affecting fish growth are manifest as variations in in- 

 crement width (Methot and Kramer 1979, Neilson and 

 Geen 1982, 1985, Radtke 1987). The response of incre- 

 ment width to short intervals of starvation indicate that 

 sagittae of Atlantic menhaden larvae may provide a 

 reliable record of short-term (e.g., days) changes in 

 feeding. The response time to starvation of Atlantic 

 menhaden larvae examined in our study was rapid. In- 

 crement width of larvae starved for only 1 day declined 

 significantly compared with fed larvae. The response 

 time of increment width to cessation of starvation 

 varied with the age of larvae. Mean increment width 

 of larvae in the young age class increased to that of 

 the controls within 3-4 days after starvation. Mean 



increment width of larvae in the older age class in- 

 creased less rapidly after starvation than did that of 

 the younger age class and did not reach that of con- 

 trols during the recovery interval (4-6 days). 



Our results indicate that microstructural growth in- 

 crements in sagittae of Atlantic menhaden can be used 

 to infer the dynamics of larval growth. In particular, 

 examination of sagittal microstructure can be used to 

 estimate the age of individual larvae from first feeding, 

 detect stressful periods, and reconstruct the growth 

 rate chronology of Atlantic menhaden larvae. We are 

 currently investigating short-term (e.g., days) varia- 

 tions in growth rate of sea-caught Atlantic menhaden 

 larvae, inferred from analysis of sagittal microstruc- 

 ture, in relation to meteorological and oceanographic 

 variables (Checkley et al. 1988, Maillet 1988). Measure- 

 ments of individual growth increments, although tedi- 

 ous to obtain, may allow inference about important 

 events during the early life stages of fish. Variations 

 in the width of growth increments from otoliths of fish 

 larvae collected in nature could be analyzed for corre- 

 lations with the timing of particular developmental 

 and environmental events to determine their relative 

 importance. 



Acknowledgments 



We would like to thank the Beaufort Laboratory of the 

 Southeast Fisheries Center, National Marine Fisheries 

 Service, for use of their larval fish rearing facilities. 

 Assistance in laboratory experiments with Atlantic 

 menhaden was given by W.F. Hettler and A.B. Powell 

 who provided fertilized eggs of Atlantic menhaden and 

 helpful advice on rearing larvae in the laboratory, and 

 C. Lewis who supplied algae and rotifers for feeding 

 young larvae. 



K.M. Mason provided expertise in the laboratory 

 and constructive criticism of the manuscript. Drs. S. 

 Warlen, S.E. Campana , and J.D. Neilson provided 

 helpful advice in otolith preparation techniques. We 

 thank Dr. D.L. Kamykowski for use of the camera and 

 video equipment for viewing otoliths. Dr. D.A. Dickey 

 provided assistance with statistics. Drs. L.B. Crowder 

 and D.L. Kamykowski made helpful and constructive 

 comments on the manuscript. This research was sup- 

 ported by a grant from the National Science Founda- 

 tion to D.M. Checkley, Jr. (OCE-85-16799). 



