Jearld et al.: Early growth, behavior, and otolith development of Pleuroneaes amencanus 



69 



Figure 4 



(A) Otoliths taken from winter flounder Pleuronectes amerkanus embryo 13d after 

 spawning, showing primordial granules in center. (B) Rings in otolith taken from em- 

 bryo 16 d after spawning. Magnification 1000 x. 



Otolith development 



Pre-hatch formation All three pairs of otoliths were 

 present in embryos as early as 13 d after spawning. 

 Premordial granules of material were evident at this 

 time, clumped together in the otolith core (Fig. 4A). 

 The periphery of the otolith forms a rather irregular 

 sphere. Up to four growth rings could be seen on some 

 embryonic otoliths (Fig. 4B). Similar formations have 

 been found on embryonic otoliths of several other spe- 

 cies (Taubert & Coble 1977, Brothers & McFarland 

 1981, Radtke & Dean 1982, Geffen 1983, Brothers 

 1984), but their periodicity or significance has not yet 

 been determined. 



Shape change at metamor- 

 phosis At the time of eye mi- 

 gration (40-50 d posthatch), the 

 sagittae of winter flounder un- 

 derwent a profound change in 

 shape. Clumps of what seemed 

 to be amorphous calcareous ma- 

 terial accumulated at the otolith 

 periphery. These accessory 

 growth centers developed irregu- 

 larly, sometimes appearing two 

 or three on an otolith, often 

 forming at 90° intervals around 

 the circumference of the previ- 

 ously round otolith (Fig. 5A). 

 Similar observations have been 

 made in other Pleuronectids 

 (Brothers 1984, Campana 1984c). 

 It is significant that accessory 

 growth centers were found only 

 on otoliths of flounders during 

 and after metamorphosis. Lar- 

 vae with symmetrically-placed 

 eyes did not show these irregu- 

 lar formations on their sagittae, 

 even as late as 73 and 76 d 

 posthatch (Fig. 5B). A photo- 

 graph of a non-metamorphosing 

 73d-old larval otolith without 

 accessory growth centers is com- 

 pared with that of the typical 

 otolith from a metamorphosing 

 individual in Figure 5. The ap- 

 pearance of asymmetrical forma- 

 tions on sagittae of metamor- 

 phosing flounders coincides with 

 the change from vertical to hori- 

 zontal orientation (i.e., dorsal- 

 side uppermost to right-side up- 

 permost) which accompanies the 

 shift to an asymmetrical form 

 and a benthic habitat. Thereaf- 

 ter, accretion again seems to proceed by increments 

 which coincide with age in days, but which continue an 

 asymmetrical deposition until the adult shape is stabi- 

 lized. If the formation of accessory growth centers is 

 found to occur at the time of metamorphosis in other 

 flounder species (Brothers 1984, Campana 1984c), this 

 may prove useful in marking the point of habitat change 

 within the otolith record. It is possible that accurate 

 otolith counts could then begin with the juvenile stage 

 rather than the earlier, less easily prepared, and counted 

 larval otoliths. 



Fish length/otolith length relationship during the 

 first year The relationship between sagitta size (larg- 



