ACTIVITY AND FEEDING BEHAVIOR OF THE 

 SUMMER FLOUNDER {PARALICHTHYS DENTATUS) 

 UNDER CONTROLLED LABORATORY CONDITIONS 



BoRi L. Olla, Carol E. Samet, and Anne L. Studholme* 



ABSTRACT 



A group of five to six adult summer flounder, Paralichthys dentatus (Linnaeus), held 

 under controlled laboratory conditions in a large, experimental, seawater tank, exhibited 

 three general behavior patterns: (1) resting, (2) swimming, and (3) feeding. While 

 resting on the sand surface, the fish maintained varying degrees of alertness, indicated 

 by the position of the head and/or eye movements. Fish buried beneath the sand were 

 considered to be in a lower state of responsiveness. The fish swam and glided at all levels 

 in the water column or combined crawling and swimming to move along the sand. Ac- 

 tivity measurements based on these swimming patterns indicated that the fish were pri- 

 marily day-active. A range of feeding behaviors enabled the fish to capture prey equally 

 well on the bottom or in the water column. The significance of these patterns and their 

 relation to those of other flatfishes is discussed. 



Until recent years, knowledge about the behavior 

 of marine flatfishes has come mainly from the 

 artalyses of catches by fishing and research ves- 

 sels to determine population structure, rates of 

 recruitment, growth and mortality, migratory 

 habits, and other aspects of life history from egg 

 to adult stages. However, there are many ques- 

 tions that have been left unanswered, especially 

 those concerning patterns of behavior that in 

 many cases have a direct bearing on life habits. 

 One approach to answering questions on be- 

 havior is to observe the animal in the laboratory, 

 under controlled conditions. Recent comprehen- 

 sive laboratory studies on flatfishes have included 

 work by Kruuk (1963) on Solea vulgaris; de 

 Groot (1964) on Plenronectes platessa; de Groot 

 (1969) on Solea solea, Limanda limanda, Pleuro- 

 nectes platessa, P. flesus, Scophthalmtis rhom- 

 bus, and S. maximus; and Verheijen and de 

 Groot (1967) on Pleuronectes platessa and P. 

 flesus. A most valuable paper by de Groot 

 (1971) reviews the literature and discusses food, 



^ National Marine Fisheries Service, Middle Atlantic 

 Coastal Fisheries Center, Sandy Hook Laboratory, High- 

 lands, NJ 07732. 



Manuscript accepted May 1972. 



FISHERY BULLETIN: VOL. 70, NO. 4, 1972. 



feeding behavior, and activity in flatfishes. 

 These investigations have pointed to the diversi- 

 ty of their habits and the importance of com- 

 parative studies in understanding the interre- 

 lations between the various species. 



In this work we have endeavored to further 

 the understanding of some specific behaviors by 

 studying, under controlled laboratory conditions, 

 the activity cycles, feeding, and general swim- 

 ming patterns of adult summer flounder, Paral- 

 ichthys dentatus (Linnaeus) , a species of major 

 commercial and recreational importance. 



MATERIALS AND METHODS 



We observed five to six adult summer flounder, 

 captured 16 to 48 km off" the coast of Maryland. 

 The fish ranged in length from 37.0 to 74.5 cm 

 and in weight from 957.0 to 5,690.0 g. 



We held the fish in an elliptical seawater 

 aquarium, 10.6 X 4,5 X 3.0 m deep with a ca- 

 pacity of 121 kliter (Olla, Marchioni, and Katz, 

 1967). To provide a suitable bottom habitat 

 for the fish, we added several layers of gravel, 

 covered by an upper layer of 0.6 to 0.8 mm sand. 

 Beneath the sand and gravel was a network of 



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