FISHERY BULLETIN: VOL. i'). NO. 2 



size of the fish were not measured and tail beat 

 frequency was measured over a limited speed 

 range. Fierstine and Walters (1968) measured 

 both tail beat frequency and amplitude of wavy- 

 back skipjack, Euthynnus affinis, from dorsal 

 cine photographs of free-swimming fish in cir- 

 cular swimming pools but only five, one-beat se- 

 quences of swimming were analyzed. 



The objective of the present .study was to de- 

 termine the relationships between swimming 



speed, fish length, tail beat amplitude, and tail 

 beat frequency in a pelagic marine fish, jack 

 mackerel, Trachurus symmetricus. To accom- 

 plish this objective, dorsal cine photographs were 

 taken of fish swimming in currents of different 

 speeds in a specially designed activity chamber. 

 For comparative purposes tests were also run 

 on three other marine fish: chub mackerel, 

 Scomber japovicns; Pacific sardine, Sardinops 

 sagax; and a shark, Triakis henlei. 



Figure 1. — .'Vpparatu.s used to measure .swimming speeds of fishes. Inset upper left apparatus shown with 

 opaque walls; center, isometric, three dimensional scale drawing, walls, deflectors and other structures are shown 

 as transparent for purposes of illustration; arrows indicate direction of current flow; and lower right, scale 

 for vertical and horizontal planes of drawing. 



254 



