OLLA, SAMET, and STUDHOLME: SUMMER FLOUNDER 



change in activity; i.e., 17 times yawning pre- 

 ceded swimming from a resting position, 2 times 

 it preceded burying, and 5 times, a change in 

 position. In seven instances, 5 to 10 min elapsed, 

 before the fish proceeded to bury (2 times) , swim 

 (4 times), or change position (once). The re- 

 maining two instances occurred as the fish set- 

 tled on the sand after swimming. It appeared 

 from these findings that yawning generally was 

 associated with changes in activity. This is sim- 

 ilar to the increased activity following yawning 

 in the yellowtail demoiselle. Micros pathodon 

 chrysurus, (Rasa, 1971). 



The buried position was characteristic of fish 

 in a state of low responsiveness, similar to that 

 shown by fish lying flat on the surface of the 

 sand. The eyes seldom rotated and a buried 

 fish did not respond to prey that moved or settled 

 directly within its line of vision. Burying be- 

 gan with an upthrust of either head or tail which 

 continued as a beating of the head and tail alter- 

 nately against the sand, from 5 to 10 times, until 

 the fish was partially or completely covered. 

 This took 1.5 to 3.0 sec. 



The events leading to burying were apparently 

 nonspecific. For instance, after swimming, some 

 flounder would settle on the sand and immedi- 

 ately bury. Other flounder resting on the sand 



for as long as 20 min would, for no reason ap- 

 parent to the observer, bury. We also found 

 that, as described below, burying might occur* 

 as a secondary response when the fish were sub- 

 jected to an intense or sudden stimulus. 



SWIMMING 



Swimming movements could begin from any 

 resting position and could be classified into three 

 categories. In one category, fish swam in the 

 water column, at any depth from surface to bot- 

 tom, at speeds ranging from 19.0 to 58.0 cm/sec. 

 As a fish swam, the head moved up and down 

 while the body musculature expanded and con- 

 tracted, the whole process viewed as a series of 

 rhythmic undulations. The caudal fin exerted 

 most of the momentum for forward movement; 

 the left pectoral (the eyed side) and to a lesser 

 extent, the right pectoral, acted as rudders. To 

 counteract their natural negative buoyancy, and 

 hence the tendency to sink, the fish were contin- 

 ually in motion, swimming at one level or swim- 

 ming upward, 



A second type of swimming combined active 

 propulsion and gliding. The fish would swim 

 upward in the water column (Figure lA and B) 

 and then, by positioning the head downward and 



Figure 1. — Swimming and gliding behavior. A swimming fish (A, B) flexes from head to midsection (C) to begin 

 a glide. As the head drops (D) and the body flattens (E), the fish glides downward and forward (F, G). At any 

 depth, the fish can either resume swimming (H) or brake its forward glide (I). 



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