Swimming-speed studies of herring 

 ( Clupea harengus ) using a circular rotating 

 trough are in progress at the Bureau of 

 Commercial Fisheries Biological Laboratory 

 at Boothbay Harbor, Maine. Fish are placed 

 in a specially designed cage (20 inches long 

 by 3 3/4 inches wide by 7 inches high), so 

 constructed that it fits within a section 

 of the rotating trough, but permits water 

 to enter and leave. The cage provides ex- 

 cellent opportunity for observation of fish 

 behavior. It also eliminates visual refer- 

 ence points on the trough. To determine 

 the water velocity through the cage (and if 

 desired, the velocity of the water in the 

 trough itself), it was necessary to have a 

 device which could fit easily within the 

 cage and could be used in salt water. 



Previous methods for water velocity 

 determinations in circular tank experiment? 

 are subject to several limitations. The 

 technique used by Regnard (1893), based on 

 the assumption that water rotating in the 

 vessel was moving at the same velocity as 

 the vessel itself, does not correct for the 

 decided lag that exists between the speeds 

 of the container and the water rotating 

 in the container. The methods used by Fry 

 and Hart (1948), Davidson (1949), and Brett, 

 Hollands, and Alderdice (1958), although 

 able to measure surface water velocities, 

 cannot be used to determine any differences 

 in velocities which might exist between sur- 

 face and lower water layers. To date the 

 Leupold and Stevens meter used by Paulik, 

 DeLacy, and Stacy (1957) has been the best 

 reported method for determinations of water 

 velocities in the fish wheel experiments. 



Unfortunately , the meter is a delicate 

 instrument and must be handled with extreme 

 care. In addition, at Boothbay Harbor, it 

 has been found to be usable only in fresh 

 water, since the electrolysis that occurs 

 in salt water interferes with operation of 

 the meter by forming deposits on the con- 

 tacts. 



None of the devices used previously 

 in swimming-speed determinations meet the 

 specifications required for the present 

 studies.— For this reason, a new photo- 

 electric cell-type current meter, using a 

 modified l-?hot cathode-coupled multivibra- 

 tor circuit, has been planned, built, and 

 tested. This meter cannot be used to deter- 

 mine the velocities at the surface or the 

 immediate sides or bottom of the container. 

 However, these limitations do not appear 

 serious, for the fish swims infrequently in 

 these regions for any length of time and 

 the current being measured is that actually 

 encountered by the fish. The immersed part 

 of the meter was designed to reduce as much 

 as possible any interference with the water 

 current. 



It will be noted from the following 

 illustrations and descriptions that the 

 meter is sturdy cind small enough to fit 

 easily within the cage (previously described) 



jy Only the Gurley current meter, Model 622B-SW10 with 

 Model 609-B counter, would seem to meet with most of 

 the desired specifications. To date, use of this meter 

 in swimming -speed studies has not been reported, and it 

 was not tested in the present study. 



Figure 1. --Laboratory current meter, with parts labelled (wherever possible) to correspond with text. 



