MATERIAL AND ME'IHODS 



The fish used in these studies were one or two yellowfin 

 ( Heot hunnus macropterus ) and five little tunny (Buthyiinus yaito)^ 

 v,'hich were confined in a concrete tank (Tester 1952 )o 



A general plan of the tank is shown in figure li^o In this Aj 

 Be, C, and D are four metal baffles, painted v/hite| the longer baffle 

 D houses optical equipment Eo The seawater inlet is indicated by 

 G and its exit by H, while L and U show the positions of two 60-watt 

 electric liglit bulbs which were lit each night from dusk tc dawn<> 

 The dotted line NO indicates the position of a cord placed across the 

 tank about 1 foot above the water surface to mark off the northern 

 one-quarter of the tanko It was fastened to the slat railing which 

 surrcunded the tanko The feeding station is shovm by Fo 



The instrument box E^ shcrm in detail in figure l^j is designed 

 to carry a source of light^ a set of light filters , and shutters 

 with variable speedy submerged so as to send a beam of light of 

 desired frequency horizontally under the surface of the water from 

 one end of the tank to the other^ and to prevent seawater from coming 

 into contact with the instrumentSo The box is 24 inches long, 18 

 inches wide, and 2k inches deep., made of galvanized iron sheets sol- 

 dered at the joints^ and held rigid by a wooden frameo At first a 

 carbon arc lamp with a series of optical lenses was used as the 

 source of lighto However^ the inconvenience of having to change 

 the carbon pencil every half-hour or so led to its replacement by 

 a projection lantern,, The lantern (L in the diagram) consists of a 

 ^00-watt Mazda incandescent lamp placed in front of a concave mirror 

 and behind a series of optical lenses which concentrate the light 

 into a narrow beam of about if inches in diameter at the glass win- 

 dow Wo The lantern is connected to the 110- volt, 60 cycle power 

 line through a powerstat (variable transformer) which has the follow- 

 ing specifications; output range^, 0-135 volts^ maximum amperes^ 7o5i 

 output KVAj 1;: frequency, 50/60 cycle A metal frame 1 inch larger 

 all around than the 3 x U inch glass plate used as a window Vif is sol- 

 dered on the outside of "the box over the 3~inch square opening tc 

 hold the glass in place, vfhile a patented caulking compound forced 

 into the space between glass and frame successfully makes the window 

 water tight. On its way to the window the light beam passes through 

 a shutter S which is a circular disc of aluminum carrying four open- 

 ings, each ij Inches in diameter and placed equidistally one in each 

 quadrant. The axis of the disc is mounted agairst a friction disc 

 F connected with a 3~inch pulley P, By changing the point of contact 

 between ths friction wheel and a fixed ring on the axis of the shut- 

 ter the speed of rotation of the shutter can be changed at will from 

 no motion/ when the point of contact is at the center of the friction 

 wheel, to maximum speed, when the contact is at its rimo By select- 

 ive use of either one, or two, or all four openings m the shutter, 

 the rate of interruption of light can be increased Uuree-fold, A 



37 



