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



73 



vation of darting in bottom-resting fish 

 occurred on day 54. Darting persisted as 

 a sporadic activity in metamorphosed ju- 

 veniles. 



Metamorphosing fish fed in the water 

 column as did unmetamorphosed larvae. 

 Feeding behavior was observed through- 

 out the daylight period. Other research- 

 ers have noted the strictly diurnal feed- 

 ing behavior of young winter flounder 

 (Laurence 1977). 



Newly metamorphosed fish resting on 

 the bottom were observed "gulping" on 

 day 55. Gulping was a relatively inactive 

 feeding behavior, with the jaw gape and 

 snap found in the lunge but not accom- 

 panied by other body movements. Post- 

 metamorphic juveniles increased the in- 

 cidence of gulps with age, sometimes 

 combining a short creep and a gulp but 

 often showing no other sign of active feed- 

 ing. After metamorphosis is complete, in- 

 creased feeding efficiency, coupled with 

 decreased metabolic requirements, re- 

 sults in comparatively low energy expenditures associ 

 ated with feeding behavior (Blaxter & Staines 1971 

 Laurence 1977). 



Conclusions 



In this study, larval winter flounder otoliths were found 

 to reflect internal and external changes indirectly. Daily 

 growth increments did not begin immediately after 

 hatching, although some individuals exhibited otolith 

 rings at hatch. Daily growth increments were not vis- 

 ible beginning at yolksac absorption. Rather, incre- 

 ments were visible beginning at a point midway be- 

 tween yolksac absorption and the beginning of 

 metamorphosis. These increments may have reflected 

 internal changes presaging metamorphosis, although 

 such changes are not yet externally evident. The pe- 

 riod during which these increments appeared was also 

 the period during which swimming behavior during 

 the day became constant, except when it was inter- 

 rupted by feeding behavior. Shortly after this time- 

 period, the slow "S motion" was first exhibited as a 

 feeding behavior, possibly correlated with experience 

 and better feeding efficiency. 



Metamorphosis resulted in obvious behavioral 

 changes as well as anatomical ones. Swimming began 

 with an upright position in which the tail was whipped 

 back and forth to provide propulsion. Larvae then went 

 through a period of canted swimming before settling 

 into swimming on their sides using a rippling of their 



'/.UNMETAMORPHOSED LARVAE 

 RESTING ON BOTTOM 



% OEVELOPING {EYE ASYMMETRICAL) 

 OR METAMORPHOSEO FLOUNDER 

 RESTING ON BOTTOM 



70 80 90 



POSTHATCH AGE, DAYS - 



100 



Figure 9 



Swimming vs. resting behavior of pre-metamorphosed versus developing (eye 

 asymmetrical I or post-metamorphosed winter flounder Pleuronectes americanus. 

 3-18 fish were observed in each 10 min period. Average number observed/period 

 was 7. 



fins for most propulsion. Horizontal swimming with 

 rippling fins was associated with the change to a more 

 benthic existence. The horizontal swimming style oc- 

 curred less frequently than the earlier upright one, 

 which was consistent with a decrease in overall activ- 

 ity levels. Individuals spent increasing amounts of time 

 resting on the bottom as metamorphosis progressed. 

 At this time, slow bottom "creeping" was first exhib- 

 ited along with the relatively inactive "gulping" feed- 

 ing behavior. 



The external changes in body shape at metamor- 

 phosis corresponded with internal change in sagittae 

 shape. Otoliths from metamorphosed juveniles were 

 found to exhibit accessory growth centers. Sagittae from 

 older fish that had not yet undergone metamorphosis 

 did not exhibit these centers and consequently were 

 still spherical. 



The connections between fish growth, behavioral ecol- 

 ogy, and physiology are still not well understood. There 

 is clearly a connection between behavior and physiol- 

 ogy, although the causality of change in morphology, 

 growth, and behavior is still unclear. This study at- 

 tempted to correlate some of the behavioral and ana- 

 tomical changes. 



Acknowledgments 



We gratefully acknowledge the technical assistance pro- 

 vided by the staff of the Fishery Biology Investigation 

 of the Northeast Fisheries Science Center, National 



