BREEDING HABITS OF RAINBOW DARTER. 39 



darker than later in the season, but are inconspicuously mottled 

 with dark colors on an olive or brown background. In the young 

 male the first dorsal often shows a dark blue color, the first bright 

 color to appear. But the breeding males (Fig. i)take on brilliant 

 shades of red, orange, blue and green. As Holt (1898) states 

 for Callionymus, so also in the male of Etlieostoma, the back re- 

 tains its mottled brown appearance, while the color pattern of 

 the sides and fins becomes very brilliant. The blue of all parts 

 becomes more intense and is of a bright peacock shade except 

 where apparently darkened by black as in the bars and the 

 ventral fins. The reds also become in places a bright orange. 

 The most brilliant colors were observed the first part of the 

 season. Besides these seasonal changes, there are many indi- 

 vidual variations. The blue of the first dorsal may cover the 

 whole fin so as to obliterate the pattern. The blue bands across the 

 posterior part of the body may be six or four instead of five ; the 

 red which alternates with these may form intervening bands or may 

 occur in patches above and below the lateral line ; the caudal fin 

 which is sometimes light greenish blue may have two pale red or 

 yellow lines radiating from the base of the fin. In addition to 

 individual variations and seasonal changes there are changes in 

 color tone which occur from day to day or from moment to mo- 

 ment. (1) The ground color in both sexes varies in tone with 

 the color of the bottom. Thus it is dark on an ooze covered 

 bottom, but when the high water sweeps away the ooze and ex- 

 poses the underlying yellow sand the color of the fish becomes 

 lighter in harmony with the bottom. (2) The colors are more 

 brilliant when the temperature of the water is low. This change 

 of color with decrease of temperature does not appear to coincide 

 with increased spawning activity, since spawning was not ob- 

 served when the water was below 15 C. The brilliant colors 

 coincide rather with the low temperatures of the early part of the 

 season before the actual spawning. Besides this the brilliant 

 colors of the males, especially the blues often flash out mo- 

 mentarily and fade again when the rivalry between them is most 

 intense, as described below. 



In the spring the darters leave their lurking plaees in the rapids 

 and congregate on the gravel sheets which are spread out at the 



