Abstract. — Studies were per- 

 formed to determine effects of envi- 

 ronment and physiology on the for- 

 mation of daily increments in winter 

 flounder otoliths. Otoliths from 

 embryonic to 1-yr-old laboratory- 

 raised winter flounder Pleuronectes 

 amehcanus and young-of-year wild- 

 caught specimens were examined, 

 and growth patterns were deter- 

 mined from photographs taken on 

 light and scanning electron micro- 

 scopes. Behavioral observations were 

 made from hatching through meta- 

 morphosis. 



Daily growth increments of oto- 

 liths from larval winter flounder 

 were enumerated, and a growth 

 curve was derived describing the 

 first 2 months of life. Growth was 

 best described by a Gompertz-type 

 curve. The relationship between 

 sagitta size and fish length was ex- 

 ponential for larvae, but linear dur- 

 ing the remainder of the first year. 

 Sagittae were compared with fish 

 length for both wild and laboratory- 

 reared juveniles and exhibited the 

 same relationship for each. The 

 change in relationship between 

 sagitta size and fish length coincided 

 with changes in dimensional growth 

 of the fish. 



During metamorphosis, swim- 

 ming and feeding modes changed 

 from tail-propelled, upright swim- 

 ming and frequent sudden feeding 

 lunges in larvae, to bottom-resting 

 and creeping accompanied by infre- 

 quent feeding gulps in juveniles. 

 This change reflected the transfer 

 from pelagic to benthic habitat and 

 anatomical transformation to asym- 

 metrical form. In general, juveniles 

 maintained lower activity levels than 

 did larvae. Behavioral and anatomi- 

 cal changes are summarized. 



Early growth, behavior, and 

 otolith development of the winter 

 flounder Pleuronectes amehcanus 



Ambrose Jearld Jr. 



Woods Hole Laboratory, Northeast Fisheries Science Center 



National Marine Fisheries Service. NOAA 



1 66 Water Street. Woods Hole. Massachusetts 02543-1 097 



Sherry L. Sass 



Division of Marine Fisheries, 1 8 Route 6A 

 Sandwich, Massachusetts 02563 



Melinda F. Davis 



Biology Department. Fort Valley State College 

 Fort Valley, Georgia 3 1 030 



Manuscript accepted 4 November 1992. 

 Fishery Bulletin, U.S. 91:65-75 1 1993). 



Many aspects offish development are 

 reflected in otolith structure. Short- 

 and long-term changes in growth rate 

 may be caused by either environmen- 

 tal fluctuations or life history changes 

 (e.g., metamorphosis, spawning), and 

 these events may also be incorporated 

 into the otolith record of sagittae. 

 Hyaline bands have been used for 

 decades to estimate age. Daily growth 

 increments have also been discovered 

 in fish otoliths (Pannella 1971, 1974) 

 and are proving a powerful tool to 

 study larval population dynamics. 



One daily growth increment in- 

 cludes both a calcium-rich aragonite 

 layer in a protein-poor matrix (the 

 "incremental zone") and a poorly cal- 

 cified protein-rich matrix layer (the 

 "discontinuous zone") (Watabe et al. 

 1982). Increments are entrained in 

 response to a 24 h light/dark cycle 

 (Taubert & Coble 1977, Tanaka et al. 

 1981, Radtke & Dean 1982) as well 

 as influenced by other cues (Campana 

 & Neilson 1982, Campana 1984a,b). 

 As a result of the daily cycle in cal- 

 cium deposition, otoliths often reflect 

 fish age, irrespective of growth, al- 

 though this has not always been 

 found to be the case (Geffen 1982, 

 Campana 1983, Jones 1984). Differ- 

 ences in width and other features of 



daily growth increments have been 

 correlated to life-history transitions, 

 changes in environmental conditions 

 such as temperature and ration size, 

 and physiological factors (for review 

 see Campana & Neilson 1985, Jones 

 1986). 



Flounders have a particularly com- 

 plex first year because, not only their 

 habitat, but also much of their body 

 form and behavior changes drasti- 

 cally at metamorphosis ( 35-56 d af- 

 ter hatching). Hatching as symmetri- 

 cal larvae that feed planktonically, 

 they begin to frequent the bottom as 

 their dorsoventral dimension in- 

 creases, the notocord tip bends, and 

 the adult-shaped caudal fin develops 

 (Klein-MacPhee 1978). Finally, the 

 fish spends less time swimming in 

 the water column and becomes 

 benthic. This occurs as one eye mi- 

 grates across the dorsum to the op- 

 posite side of the head and the juve- 

 nile flounder orients at a 90" angle 

 to its previous alignment. Otoliths do 

 not change their position in the head 

 during this transformation (Piatt 

 1973, Policansky 1982), so the 

 sagittae end up lying one over the 

 other. Evidence of the fish's orien- 

 tational change may be reflected in 

 the otolith depositional pattern. 



65 



