60 



ftquattc JLitt 



medium-sized all-glass aquarium on the 

 top of my desk. From day to day or from 

 hour to hour I have watched it change 

 its color-pattern back and forth, from 

 one type or phase to another, each ap- 

 pearing like the marks of a distinct spe- 

 cies. When kept in the dark, either dur- 



Striped Phase 



ing the night or during the day (by cov- 

 ering the sides and top of the aquarium 

 with pasteboard), the whole complement 

 of dark colors is brought out, as shown 

 in the figure at the head of this article: 

 a black lateral streak, extending from the 

 tip of the snout to the base of the caudal 

 fin, is crossed by about thirteen dark 

 bars; the fins, too, are largely blackish. 

 The darkest color and most extensive pat- 

 tern, it thus appears, are displayed in a 

 similarly dark environment. The darken- 

 ing of the fish by darkening the tank in 

 the daytime would seem to indicate that 

 light, rather than temperature, influenced 

 the change. 



In the morning hours the little sucker 

 actively swims about in the increasingly 

 bright light of the aquarium, usually in 

 clear water away from weeds and stones. 

 The vertical bars now more or less grad- 

 ually fade out, leaving the back a nearly 

 uniform dark shade, separated by a 

 bright streak from the black lateral band 

 or stripe, which thus by contrast is ren- 

 dered very inconspicuous. Can this pat- 

 tern tend to conceal the fish in open 

 water? Though we cannot be certain in 

 our answer, it appears probable that this 

 black stripe enters the classification of 



"ruptive" markings, that is, those that 

 conceal an animal or other object by 

 breaking its outline in two, making it 

 appear what it is not. To produce 

 analagous results, a camouflage artist 

 paints a black streak, or several of them, 

 across a field gun. Though conspicuous 

 in itself, the marking is concealing in ref- 

 erence to the fish — or to the gun, de- 

 pending on whether Nature or Man is 

 the artist. 



Under certain conditions the chub- 

 sucker loses the black longitudinal stripe, 

 but gains in its stead a series of vertical 

 bars. It is hard to believe that this barred 

 fish is the same individual as the streaked 

 one observed before. But it really is the 

 self -same fish, exhibiting another and dis- 

 tinct color pattern. By combining the 

 bars and stripes, the chub-sucker develops 

 the complete color pattern illustrated at 

 the head of this article. 



We have not yet exhausted the color 

 phases which the young sucker is able to 

 display at appropriate times. Often when 

 browsing over a gravelly bottom it takes 

 on a blotched appearance. This blotched 

 phase, it appears on a moment's analy- 



Barred Phase 



sis, combines features of both the barred 

 and striped phases. As the blotches ren- 

 der the fish extremely inconspicuous 

 (under natural top light) against the 

 gravel background, it is obvious that we 

 are dealing here with a typical example 

 of concealing coloration. 



Thus we discover that the young chub- 

 Concluded on page 62. 



