FISHERY BULLETIN: VOL. 70, NO. 4 



pipes designed to move filtered water through 

 the layers to prevent contamination of the bot- 

 tom. Water temperature in the tank ranged 

 from 17.0° to 20.0°C. Salinity ranged from 23.0 

 to 26.0^/f, oxygen from 6.5 to 7.7 mg/liter, and 

 pH from 7.3 to 7.7. 



Fluorescent lights mounted on two side walls 

 above the aquarium were mechanically timed to 

 approximate the natural daily photoperiod from 

 morning to evening civil twilight. Since Ver- 

 heijen and de Groot (1967) reported that high 

 light intensities could inhibit normal activity in 

 flatfish, we held the maximum daytime light in- 

 tensity, as measured at the surface, at 3.5 X 10^ 

 mc. Preliminary measurements showed this 

 level not to be inhibitory. An automated dim- 

 ming system gradually raised and lowered light 

 intensity during morning and evening civil twi- 

 light, avoiding sudden light changes that might 

 startle the fish. A second lighting system, which 

 switched on before the dimmer lights were ex- 

 tinguished, provided an indirect light of 2 X 

 10 ~^ mc as measured at the water surface (2.5 

 X 10"^ mc at 1 m below the surface) during 

 the night period. 



Throughout the course of the observations, at 

 intervals of about 30 days, we fed the fish 1,100 

 to 4,400 g of live sand shrimp, Crangon septem- 

 spinosa, and grass shrimp, Palaemonetes vulgar- 

 is. The quantity of shrimp introduced each time 

 insured a food supply which lasted for 30 days. 

 According to Poole (1964) and Smith (1969), 

 shrimp appear to be an important constituent 

 of this species' natural diet. 



Following 34 days of acclimation to the tank, 

 we measured the activity of six fish over a 51-day 

 period. At the end of this time, one fish died 

 and our measurements were then based on five 

 fish. Throughout the day and night, we made 

 5-min observations every hour 4 days each week 

 of the number of fish swimming, feeding, or mov- 

 ing about on the bottom. 



We found that 5 min was too brief to allow 

 for extensive observations of the fish's behavior, 

 so after establishing the daily cycle of activity, 

 we lengthened these periods to 30 min every 3 

 hr 4 days each week. In conjunction with these 

 extended observations, we periodically took mo- 

 tion pictures which allowed us to make a more 



detailed analysis of feeding and swimming. 

 Gliding and swimming speeds were measured 

 from these motion pictures as well as from stop- 

 watch readings taken as the fish passed between 

 two marks 335 cm apart. 



RESULTS 



We have classified the activity patterns of the 

 fish into three general categories: (1) resting, 

 either on the surface of the sand or beneath it, 

 (2) swimming, and (3) feeding. Within these 

 three categories, we have described the various 

 aspects of each behavior in an attempt to pro- 

 vide a clearer picture of the fish's habits. 



RESTING 



The summer flounder exhibited three basic 

 resting positions: (1) lying flat on the sand; 

 (2) lying on the sand with the head raised (as 

 much as 7.5 cm), supported by the body mus- 

 culature and the anterior portions of the dorsal 

 and anal fins braced vertically into the sand; 

 and (3) buried beneath varying amounts of 

 sand. 



In the first resting position, while flat on the 

 sand, the eye turrets were either retracted or 

 extended. When extended, the eyes either re- 

 mained relatively fixed or moved up to 6 to 8 

 times per min. When the head was raised, as 

 in the second resting position, eye movements 

 were generally more frequent, ranging from 10 

 to 30 times per min, reflecting a higher degree 

 of responsiveness. This "head-up" posture was 

 generally characteristic of an animal at a higher 

 level of activeness than fish lying flat. 



Fish in either resting position occasionally 

 "yawned." The head was elevated, the mouth 

 opened, and the opercula extended. Yawning 

 occurred either as a single event or up to 16 times 

 in rapid succession. As yawning was repeated, 

 the gape of the mouth increased and the head 

 rose progressively farther off the sand. During 

 the 30-min observation periods, we recorded the 

 events preceding and following 33 yawns, i.e., 

 separate occurrences, whether comprised of a 

 single yawn or a number of successive yawning 

 movements. Of these, 24 preceded an immediate 



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