FISHERY BULLETIN: VOL. 74, NO. 3 



disturbances outside their container. Tliere is no 

 reason to suppose that the results were so 

 influenced. 



Two grams of the dry granular Polyox were 

 dissolved in a small portion of the synthetic 

 seawater. This was then returned to the test 

 aquarium by allowing it to drip back by means of a 

 siphon tube nearly closed by a screw clamp. The 

 final concentration of Polyox in the aquarium 

 became approximately 42 ppm. 



A motion picture camera facing down was 

 erected so that its optical axis was over the 

 geometric center of the tank. Photo floodlights 

 were set up as required. The view included most of 

 the aquarium, omitting only the ends of the tank 

 where the fishes were forced to turn back, as these 

 tests must be made with the fishes moving in a 

 nearly straight line. Also included in the camera's 

 coverage were tapes marked in centimeters. One 

 ran along the top edge of the tank and the other 

 along its bottom, thus providing an index to the 

 lengths of the fishes and their distances of travel. 

 The aquarium had its sides blocked with bluish 

 cardboards, except on the sides toward the lights. 

 These were higher than the aquarium and off to 

 one side sufficiently to eliminate reflections into 

 the camera's lens. The test fish were added and 

 allowed to adjust to the new situation for about 1 

 h. The tank in which they had lived for at least 1 

 wk was identical with the test tank, except that it 

 had all four sides covered with similar cardboard 

 guards. 



Photographs were taken after the lights had 

 been turned on gradually to full voltage. It was 

 found by experience that normal film speed was 

 fully adequate for our analysis. Sufficient footage 

 was exposed to insure an adequate number of 

 straight runs of single fish. 



When the above procedures were completed, the 



Polyox was allowed to drip into the tank, which 

 took about 10 min. After 1 h had elapsed, its 

 mixing was considered completed, for in addition 

 to the aerating devices, the four very active fishes 

 provided continuous mixing. After this time in- 

 terval the photographic procedures were repeated 

 and the experiment was terminated. 



The results of these experiments are given in 

 Table 4 and their analysis is illustrated by graphs 

 in Figure 21. Graphs A and C clearly show the 

 difference between fishes swimming in synthetic 

 seawater, initially devoid of any long-chain 

 polymers, and in the same water to which the 

 polymer has been added. The speed of the fishes is 

 approximately double in the latter, as are the tail 

 beats. In this experiment, after the first run (Si) 

 was made in synthetic seawater, the tank with its 

 contained fishes was left as it was until 2 days later 

 when another run (S2) was made. The new speed 

 readings were a little higher, but the proportional 

 corrections were not. If more refined measure- 

 ments show that a small difference is measurable, 

 it should be due to the additions of organic sub- 

 stance in the interim, consisting of the body 

 wastes of the fish as well as their own surface slime 

 produced in this period. Added to this must be the 

 dissolved matter from the food given to the fishes. 

 To minimize all this, all particles not consumed di- 

 rectly were meticulously removed. The manner of 

 handling data was that of Bainbridge (1958). The 

 greater refinements of the methods of Hunter and 

 Zweifel (1971) were not deemed necessary for the 

 present simple purposes. Because of the large 

 differences between the speeds of fishes in the 

 same water, with and without long-chain 

 polymers, the slight possible spreading of the 

 caudal fin in this species could not increase the 

 area of the tail by more than a negligible amount 

 in these experiments. Later another set of four 



Table 4.-Calculations based on experiments on drag reduction in Brevoortia by polymers. TL = total 



length. TB = tail beats. 



496 



