96 The Life Story of the Fish 



fish, and everyone knows that when a phoebe darts after a 

 moving insect in the air, its beak comes together with a snap 

 not behind its prey or in front of its prey, but on it. 



We have not yet said a word about a very important 

 point. Can fish tell color? There have been more experiments 

 on this than on any other phase of the fish's vision, and 

 hotter debate, and the answer is, Yes, at least in so far as 

 the fisherman is concerned. 



Color experimentation can be very simple. Aquarium fish 

 have been taught to take food when offered on blue forceps, 

 avoid it when offered on red. Native fish at the Tortugas 

 have been taught to come to a certain place for feeding, and 

 to take food when dyed one color, but not another color. 

 The method in each case is to make the food associated with 

 the undesired color in some way unpalatable, and the as- 

 sumption is that it is the fish's discrimination between the 

 two colors which enables him to leave the unpalatable food 

 alone. 



One of the prettiest demonstrations of color discrimina- 

 tion was offered by the aforementioned jewel. The young 

 of this species, while still in the herding stage, will assemble 

 around the parent if the latter gives a sharp, quick move- 

 ment of the fins. The parent at this stage is bright red. In a 

 closely related species, Cichlasoma bimaculatum, the young 

 will obey the same signal, but the outstanding color of the 

 parent at this stage is an intense, very dark blue. A small 

 tank was rigged up with two metal disks, one just outside 

 the glass at each end. One was red, the other dark blue. By 

 means of a mechanism, the disks were made to give periodic 

 sharp jerks. If young jewels were put in the tank they soon 

 assembled at the end where the red disk was in operation. If 

 cichlasomas were put in the tank, they assembled at the blue 

 end. If both were in the tank at the same time, they separated 

 out at the blue and red ends very nicely according to species. 



