A PHOTOELECTRIC CURRENT METER 



by 

 H. C. Boyar and F. E. Schueler 



ABSTRACT 



A need for an accurate measure of water velocity in circular rotating tank experiments with 

 marine fishes led to the construction of a current meter, in which the revolutions of a propeller are 

 detected photoelectrically . Its design and operation permit measurements to be made of the cur- 

 rents encountered by fishes in laboratory and field tests. 



INTRODUCTION 



Studies designed to determine inaximum 

 swimming speed and endurance of fishes have 

 resulted in the development of various 

 types of rotating circular troughs, popu- 

 larly knovm as "fish wheels." Most of these 

 wheels operate on one basic principle. Fish 

 are placed in the water-filled trough section 

 of the wheel, which is then rotated about 

 a vertical axis. If a fish is positively 

 rheotactic, it will swim in a direction 

 opposite to the water movement, expending 

 enough energy to maintain a position with 

 respect to a fixed object in its environment. 



To determine swimming speed of a fish, 

 the velocity of the water under different 

 test conditions must be known. In the past, 

 various improvised devices and techniques 

 have been used to obtain this information. 

 As a result, some reported swimming speeds 

 may be estimates rather than absolute values. 

 Some recent investigators have used devices 

 which give accurate data, but which either 

 are useful only under certain conditions 

 or have one or more undesirable features. 

 With continued interest in swimming-speed 

 studies, particularly with the use of the 

 fish wheel, tliere is a need to measure water 

 currents accurately under many types of 

 laboratory and field conditions. 



A number of methods have been used 

 to determine water velocities in fish 

 wheels, Regnard (1893), one of the first 



fish behaviorists and probably the first 

 investigator to use a rotating-type vessel, 

 recorded how long it took a fixed point on 

 the vessel to travel a given distance. 

 Fry and Hart (1948) determined the water 

 velocity in a rotating circular trough by 

 measuring the time required for a ball of 

 cotton to make one revolution in the trough 

 chamber. They stated that the final speeds 

 as measured by the trough were estimates 

 rather than absolute values. Davidson 

 (1949) measured the water velocity in a 

 circular rearing pond by means of a small 

 cork weighted with a drag of the desired 

 length, but so constructed as to float with 

 the water surface. She recorded how long 

 it took the cork to move a given distance. 

 In addition, she measured how long it took 

 bubbles and "smaller floating objects" to 

 travel the same distance. 



In the last few years, several other 

 methods have been employed. Paulik, DeLacy, 

 and Stacy (1957) determined water veloci- 

 ties in their fish wheel with the aid of 

 a Leupold and Stevens midget current meter. 

 Brett, Hollands, and Alderdice (1958) 

 reported that the water velocity within 

 their rotating trough could be measured 

 accurately by determining the velocity of 

 a small circular plastic disk having needle 

 tips radically arranged and floating on the 

 water surface with the trough in motion. 

 They confirmed their results by recording 

 how long it took drops of dye to move the 

 same distance. 



