FISHERY BULLETIN: VOL. 70, NO. 4 



an intention movement 3 min later. Then four 

 more shrimp were ingested during the next 20 

 min, followed 2 min later by two additional in- 

 tention movements. A second fish ingested 15 

 shrimp within 35 min and 2 min later made an 

 intention movement. A third fish, after ingest- 

 ing 16 shrimp in 26 min, made an intention move- 

 ment 1 min later, then fed immediately on one 

 shrimp, and 2 min later exhibited an intention 

 movement. These movements may have been 

 related to a reduction of feeding motivation as 

 a result of satiation. 



FRIGHT RESPONSE 



We observed what was apparently a "fright" 

 response to a sudden stimulus under two differ- 

 ent circumstances. In one case, there was a mal- 

 function of the dimmer lights which caused the 

 sudden onset of the daylight lights. A swim- 

 ming fish immediately dropped to the bottom 

 where it remained resting on the sand surface. 

 In another case, an observer above the tank 

 waved his arms as a fish moved about near the 

 water surface. The fish immediately dropped to 

 the sand, darkened, and assumed a rigid posture. 

 The head and caudal fin lay flat, but the dorsal 

 and anal fins were arched in two places along 

 their length. The fish remained in this posture 

 for about 45 sec during which it slowly lowered 

 first the anterior, then the posterior sections of 

 the dorsal and anal fins until they were flat. The 

 flounder then swam about 2 m away and buried. 

 In both instances, the initial response of the fish 

 to a fright stimulus was to drop to the bottom 

 and remain motionless. Burying occurred as a 

 secondary response. 



DISCUSSION 



Previous descriptions of the habits of sum- 

 mer flounder have characterized them as primar- 

 ily bottom-oriented, except for occasional sorties 

 to the surface in pursuit of prey (Bigelow and 

 Schroeder, 1953:267-270). Furthermore, this 

 species has been described as being relatively 

 immobile, except while feeding or during the 

 normal migratory period (Ginsberg, 1952). In 

 our laboratory observations, while the fish fre- 

 quently searched for and captured prey on the 



sand and also remained quiescent on the bottom 

 for long periods, they would also frequently use 

 the water column for swimming, prey search, 

 and feeding. In fact, during one part of our 

 study, the fish swam and glided for extended 

 periods throughout all levels of the tank, seldom 

 resting in any one position. 



The gliding behavior we observed could play 

 an important role for the animal in the sea. 

 After reaching the surface, the fish could travel 

 considerable distances with little or no active 

 swimming movements, using natural negative 

 buoyancy and body shape to full advantage. Po- 

 sitioning of the fins and body would control for- 

 ward speed and distance traveled. Although 

 there might have been a sacrifice in speed, the 

 gliding would represent a saving in energy as 

 compared with that required to swim the same 

 distance. Gliding would also enable the animal 

 to search for and capture prey in the water col- 

 umn more efficiently, since it could approach a 

 prey with less gross movement than would occur 

 during active swimming. This might lessen the 

 chance of eliciting escape responses from the 

 prey due to visual or mechanical stimuli. An- 

 other adaptive advantage of gliding in food 

 search might be related to the fact that the head 

 was steady, thus making it easier to keep the 

 prey in the visual field. 



Although the summer flounder were primarily 

 day-active, we observed burying, feeding, 

 shambling, and swimming both day and night. 

 Similar to the summer flounder, turbot (Scoph- 

 thalmus maximus) swim and are active on the 

 bottom primarily during the day, although both 

 activities may occur at night to a lesser degree 

 (de Groot, 1971). Verheijen and de Groot 

 (1967) and de Groot (1971) established that 

 plaice (Pleuronectes platessa) and flounder (P. 

 flesus) showed a nocturnal pattern of swimming 

 in the upper water column, while during the day 

 they would shamble or swim over the bottom 

 searching for food. Kruuk (1963) and de Groot 

 (1971) found that the sole (Solea vulgaris) also 

 had a nocturnal period of high activity under 

 both natural and artificial light. 



The method of burying in the summer flounder 

 is similar to Kruuk's (1963) description of "dig- 

 ging-in" in the sole. In the sole as well as the 



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