OLLA, SAMET, and STUDHOLME: SUMMER FLOUNDER 



feeding was always preceded by active prey 

 search. In most instances, a flounder, after se- 

 lecting a potential prey, would rest on the sand 

 with the head slightly raised. Then, while vis- 

 ually fixing on a shrimp, the fish would begin 

 to stalk, crawling on the sand towards the prey. 

 This crawling was viewed as waves of cephalo- 

 caudal movements of the dorsal and anal fins 

 (Figure 3A-D). When a fish was within strik- 

 ing distance (5-10 cm), the head was angled 

 downward or lay flat on the sand. The mid- 

 section of the body was arched, supported by 

 the caudal fin and by portions of the edges of 

 the dorsal and anal fins braced into the sand 

 (Figure 4A) . As the caudal fin beat downward 

 (Figure 4B), the fish sprang forward, mouth 

 agape and opercula spread, striking and ingest- 

 ing the shrimp (Figure 4C). Speed during the 



strike was about 40 to 50 cm/sec. After in- 

 gestion, there was continued mouth movement, 

 apparently part of the pharyngeo-esophageal ac- 

 tivity necessary for swallowing. 



Fish that were resting on the bottom, with the 

 head either up or down, would not strike at 

 shrimp even though prey were well within strik- 

 ing distance. Feeding was always preceded by 

 active search, although these fish were seemingly 

 well-adapted for a "lying-in-wait" method of 

 prey capture. 



Fish swimming 50 to 70 cm above the bottom 

 could also capture shrimp from the sand. As a 

 swimming fish (Figure 5A) visually fixed on a 

 single shrimp, speed abruptly decreased (Fig- 

 ure 5B). While the flounder was still moving 

 forward, it would tilt towards the sand at a 30° 

 to 45° angle. At this point, with the prey about 



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FiGxmE 3. — Stalking behavior. The fish visually fixes on a shrimp and 

 crawls slowly forward on the dorsal and anal fins (A-D). 



1131 



