waves created by the ship's forward motion. It is called the 

 Inui bulb after its inventor, Dr. T. Inui of Tokyo University. 



The Inui bulb has a secondary, but most useful, function. 

 Extending 10 feet forward, it makes an excellent chamber for 

 underwater observation. 



The use of the Cromwell will greatly facilitate many of the 

 Laboratory's programs. 



Behavior 



studies in the Behavior Program continued to be directed 

 toward gaining fundamental knowledge on the responses of tunas 

 and other pelagic fishes to their environment and to artificial 

 stimuli. The studies included determining sensitivity ranges 

 of vision and hearing in tunas, description and classification 

 of behavior patterns in tunas and related fish, and observation 

 of fish communities under objects adrift at sea. 



Visual acuity in tunas was tested by observing the response 

 of the fish to patterns of alternating black and white horizontal 

 and vertical bars. The experimental method, diagrammed in 

 figure 1, involves training afish to respond to a visual stimulus, 

 which is an image of either vertical or horizontal stripes pro- 

 jected on an opal glass plate placed against a tank window. 

 When the stripes are vertical, the fish is trained to swim down 

 the tank to a food-drop area where it is rewarded; when the 

 stripes are horizontal, it is trained to turn before reaching the 

 food-drop area and return to the far end of the tank. If the 

 fish fails to turn when horizontal stripes appear, it receives 

 an electric shock. The projector is turned on when the fish is 

 at the far end of the tank and turned off when it reaches a marked 

 distance from the window. Filters are used to reduce the 

 brightness of the image until the fish is no longer able to dis- 

 criminate between vertical and horizontal stripes. 



Visual acuity can be measured in fish that have been trained 

 in this manner. Skipjack show a greater visual acuity than 

 little tunny for bright targets (those with higher luminances), 

 but the visual acuities of the two species are similar with tar- 

 gets of lower luminances. 



A captive yellowfin tuna was taught to respond to under- 

 water sound in a circular tank (fig. 2). The trained fish would 

 swim by the loudspeaker placed against the tank wall and turn 

 left into the open V (shown in the figure) whenever the sound 

 was perceived. If there was no sound or the sound was too 

 soft the tuna would swim straight by the speaker. Food rein- 

 forced this learned response. At any one pitch the loudness of 

 the sound would be decreased until the tuna no longer made 



