12 



Fishery Bulletin 91(1). 1993 



*v 



A 



52 



64 68 72 



POSTHATCH AGE, DAYS - 



Figure 8 



Incidence of winter flounder Pleuronectes amerieanus feeding behaviors, average num- 

 ber of lunges in water column lA) versus average number of gulps on bottom (  ). Note 

 change in feeding behavior from frequent pre-metamorphic lunging to less-frequent 

 post-metamorphic gulping. No lunging was observed after day 72. 



the larvae began to maintain their bodies in a horizon- 

 tal position as they sank, instead of sinking in the 

 vertical, passive, nonswimming position. 



Behavior at metamorphosis: 40-60 d posthatch Eight- 

 een fish were placed in the observation tank on day 48 

 so that their behavior could be more closely monitored. 

 The following account is based on those observations. 



By 40-50 d posthatch, larval body form began to 

 change. The body widened dorsoventrally, pigment de- 

 veloped (especially over the head, jaw, gut, and fins), 

 and the end of the notocord began to bend as the adult 

 caudal fin formed. These physical changes, described 

 more fully by other researchers (Sullivan 1915, Breder 

 1922), took place concurrently with the behavioral 

 changes described below. 



The most obvious behavioral changes were seen in 

 swimming and resting patterns. Larvae up to 50-60 d 

 posthatch swam upright using the tail-whipping mo- 

 tion. The body was positioned with dorsal fin upper- 

 most, and the eye had not yet migrated. Beginning at 

 48 d, occasional interruption of swimming was noted 

 as fish drifted in the water column, usually maintain- 

 ing an upright posture but not moving fins or tail. At 

 55 d, the first observation of canted swimming was 

 recorded. Fish rose off the bottom in response to dis- 

 turbances and swam at about a 60" angle to the side, 

 then sank to the bottom again. Only larvae whose eye 



was in the process of migration 

 (asymmetrical placement) were 

 seen to swim at an angle in this 

 way, and only infrequently were 

 these individuals observed swim- 

 ming in the water column. 



Fish with obviously widened 

 bodies and adult-shaped tails be- 

 gan the transition to bottom 

 habitat just prior to eye migra- 

 tion ( -40-50 d posthatch). Eight 

 fish were observed lying on the 

 bottom by 42 d posthatch, either 

 on their ventral or left sides. Ap- 

 parently, some of these individu- 

 als returned to larval swimming 

 patterns, since only three were 

 not in the water column on day 

 48. From day 42 until the last 

 record of fish seen in the water 

 column (day 72), swimming fish 

 were seen to sink to the bottom, 

 either head-down or horizontally 

 oriented, and usually rested on 

 their left side for varying peri- 

 ods before swimming up from the 

 sand, again with an upright lar- 

 val swimming posture (Fig. 9). Other observations of 

 left-side resting have been reported as early as 10- 

 12 d posthatch (Sullivan 1915). 



Eye migration was difficult to observe precisely. It 

 has been reported (Sullivan 1915) to occur over an 

 interval of several days, and we observed that it ap- 

 peared to occur shortly after establishment of the de- 

 veloping larva on the tank bottom. Once eye migration 

 was completed, fish were never seen to swim upright. 

 However, they occasionally entered the water column 

 lying horizontally on the left side, slowly rippling their 

 dorsal and ventral fins rhythmically. 



Newly metamorphosed fish were relatively inactive, 

 lying on the bottom for 10 min or more at a time, occa- 

 sionally moving their eyes. Activity and metabolic lev- 

 els have been reported elsewhere to decrease dramati- 

 cally at this point in flounder development (Blaxter & 

 Staines 1971, Laurence 1977). The first slow bottom 

 swimming with rippling dorsal and ventral fins or 

 "creeping" activity was noted on day 55 during meta- 

 morphosis. 



Bottom-resting fish also "darted" at intervals, swim- 

 ming in a rapid burst propelled by tail beats. A dart 

 appeared somewhat like a long lunge in its sudden- 

 ness and in its generation by caudal body motions 

 rather than fin motions. Darting was also observed in 

 unmetamorphosed fish in the water column as an in- 

 frequent reaction to a disturbance. The earliest obser- 



