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Association and Color Discrimination 



in Mudminnows and Sticklebacks 



GERTRUDE M. WHITE, Ph. D. 



Observations were made on the activi- 

 ties of the mudminnow, Umbra limi, and 

 the stickleback, Bucalia inconstans, with 

 special reference to the acuteness of their 

 sense organs, their ability to form asso- 

 ciations and to discriminate colors and 

 patterns. The experiments were carried 

 on in the Zoological Laboratories of the 

 University of Wisconsin. 



In these fishes the senses of sight and 

 smell are most used in seeking food. The 

 Stickleback displays more alertness in 

 using both senses, and a much higher de- 

 gree of acuteness of the sense of smell. 

 This was tested as follows : Cloth packets 

 one of which contained meat and the 

 other cotton, were suspended at opposite 

 ends of the aquarium. The mudminnows 

 did not show that they perceived either 

 packet though they swam in close prox- 

 imity to both. 



The sticklebacks behaved differently 

 since the appearance of the packets at- 

 tracted them at once. Those fishes which 

 went towards the packet containing meat 

 darted furiously upon it, and pulled at it 

 with great excitement, but those which 

 swam in the direction of the packet of 

 cotton stopped about 4 cm. away, and 

 turned off in another direction. Only 

 once or twice did they actually snap at 

 the cotton packet. Then, perceiving the 

 struggles of the rest of the fishes with 

 the other packet, they swam over and 

 joined them. 



In the use of the sense of sight the 

 mudminnow compares more favorably 

 with the Stickleback, though the latter 

 reacts more quickly. Both pursue mov- 

 ing objects without odor, such as bits of 



paper, or objects above the surface of the 

 water ; both are stimulated by shadows or 

 an increase in the amount of illumination. 



A series of experiments were carried 

 on to discover whether these fishes pos- 

 sess color vision. The general problem 

 presented to them was that of learning to 

 associate food with a certain color, and at 

 the same time associate unpalatable sub- 

 stances, such as paper, with another color. 

 In order that there might be no chance 

 to smell the food, the bait was not drop- 

 ped into the water, but the fishes were 

 taught to leap out of water and take it 

 from forceps. Repeated trials determined 

 that the fishes were not able to distin- 

 guish between the imitation baits and the 

 food when both were offered out of water 

 under the same conditions. 



In the first set of experiments colored 

 papers were used. Discs cut 7.3 cm. in 

 diameter and stiffened with cardboard. 

 An aperture was cut in the centre of each 

 large enough to allow the discs to be slip- 

 ped down over the ends of the forceps 

 from which the fishes were fed. After 

 a mudminnow had been given food in 

 this way for some time, the appearance of 

 a colored disc became a signal for the 

 fish to dart to the surface and spring out 

 of water after food. When this associa- 

 tion with one color seemed to be thor- 

 oughly established, a disc of another color 

 was substituted, with paper closely resem- 

 bling the food in color and appearance in 

 the forceps. The fish first snapped at the 

 paper, but soon came to avoid it, and 

 refused to snap at paper or food under 

 the disc with which it had come to asso- 

 ciate unpalatable substances, though it 



