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



2.50 



6 7 



STD LENGTH (CM) 



Figure 7 



Regression of standard fish length on sagittae size for pooled 

 young-of-the-year winter flounder Pleuronectes americanus 

 (3 mo or older). Pooled data include both laboratory-reared 

 and wild collected data (n=28). Y=0.10+0.29X, r 2 =0.95. 



protecting young larvae from extensive transport by surface 

 currents (Sullivan 1915, Pearcy 1962). Sullivan reported that 

 swimming appeared to be periodically inhibited by a factor 

 other than fatigue. By 7d, larvae swam for 3-10 s followed by 

 a 2-10 s passive period. After about 25-30 d, swimming was 

 constant during the day except when interrupted by feeding 

 behaviors. 



For the first 10 d posthatch, swimming larvae were concen- 

 trated at the surface; after about 20 d, larvae were dispersed 

 throughout the water column. There were noticeable aggre- 

 gations of larvae at tank corners and along sides, but no 

 schooling behavior was observed. Swimming larvae avoided 

 bright microscope lights. 



Lunging — defined as a sudden, rapid thrusting motion of 

 the body which propels the larva less than a centimeter for- 

 ward but which is faster and more abrupt than swimming 

 activity — was observed as early as 5-7 d posthatch (depend- 

 ing on hatch group), before the mouth was completely formed. 

 Once the mouth parts had formed (at the time of yolksac 

 absorption), lunges included rapid and wide jaw gape and 

 snap. Incidence of lunging increased from less than once a 

 minute initially to once every 10 s or more frequently by 40 d 

 posthatch. Systematic observations of lunges began at day 48 

 (Fig. 8). Prey items were not always visible but were seen 

 often enough that these movements were assumed to be feed- 

 ing lunges. No lunges were observed after day 72 coincident 

 with metamorphosis. 



A sigmoid coiling of the body, called an "S motion" here, 

 often preceded the lunge. This motion could be slow or fast, 

 and when rapid often included a single side lunge as the 

 body was pulled backwards and the head whipped from one 

 side of the "S" to the other. The rapid "S" was first observed 

 5-9 d posthatch, while the slow one was not noted until 30- 

 50 d posthatch. Larval feeding by such an "S strike" motion 

 has been described for other species in the literature 

 (Rosenthal & Hempel 1970, Hunter 1972). The slow "S 

 motion" we observed in older larvae is speculated to be 

 related to the greater accuracy of striking prey facili- 

 tated by experience. 



Successful feeding, defined by observation of at least 

 one food particle in the gut of sampled larvae, began 

 at 9-14 d posthatch, at or just after yolksac absorption 

 (8-12d posthatch). However, growth has been reported 

 to slow or stop for several days after absorption of the 

 yolksac (Cetta & Capuzzo 1982). 



Passive, nonswimming yolksac larvae sank in a head- 

 down position in the water column until they hit bot- 

 tom or abruptly resumed swimming towards the sur- 

 face. When on the tray bottom, they lay on either side, 

 or on top, of their yolksac. As swimming duration in- 

 creased, time on the tray bottoms decreased until, af- 

 ter 20 d (when the yolksac was no longer present), few 

 were seen on the bottom. Passive, nonswimming be- 

 havior in the water column was, however, observed 

 past 20 d. After yolksac absorption (-12 d posthatch) 



