CHEMORECEPTION: LOCOMOTION AND ORIENTATION 



291 



Figure 13 Shark monitoring tank: radially oriented hollow dividers (A); vertical win- 

 dows (B), behind which are either fluorescent lamps and red filters (C) or banks of 

 photoconductive cells (D); peripheral channel (E) through which water is supplied to the 

 individual compartments. 



boxes are mounted banks of eight photoconductive cells, uniformly spread 

 with their photosensitive surfaces directed toward the windows of the neigh- 

 boring boxes containing the light sources. Stops in front of the photocells 

 reduce light scatter and thereby heighten the responsiveness of each cell to 

 reductions in light intensity, resulting from the passage of a fish at the level 

 of that cell. Thus, in the tank as a whole, 16 photoelectric gates are formed, 

 passage of the fish through which is recorded, with the time, on paper tape 

 by an electronic recorder. The record, therefore, reveals the time of entry 

 and exit and the number of the compartment in question. It is afterwards 

 transferred to a computer disk pack, whence it can be retrieved for analysis 

 and computation of various locomotor characteristics. Frequency distribu- 

 tion of entries, time spent in each compartment, orientation angle on leaving 

 a compartment, sequence of pathways as a function of time, and velocities 

 are examples of the information computed from the raw data. 



The main, cylindrical body of the monitor tank is surrounded by a con- 

 tinuous channel (B in Figure 13) of the same depth as the tank. Synthetic 

 seawater, treated by biological sand and diatom aceous earth filters, enters 

 channel B, where it is maintained at constant high level by a motorized valve 

 controlled by a water level sensor. The water in the channel then enters each 



