lo62 FRESH-WATER BIOLOGY 



Tahoe the dead trout eggs from the hatchery were daily thrown 

 into the lake. Wliile no fish might be in evidence a handful 

 of trout eggs was sure to bring a bullhead {Cottus heldingi) from 

 under every rock. The same thing happened when the young 

 trout fry were planted in the brooks. The adaptations of the 

 black bass, sunfish, and Amia against depredations in their nests 

 have already been given. No doubt many young fishes are eaten 

 by minnows and sunfishes. A half-starved sunfish captured in a 

 cave began to pick out the larval bhndfishes in his pail, with neat- 

 ness and dispatch, as soon as there was light enough for it to see 

 them. The herding or schooling of their young by many fishes, as 

 an adaptation against enemies, has been described before. Against 

 their predacious neighbors strength, agility, endurance, and color 

 are the adjustments. The dispersal of a school and the leap out 

 of the water, reaching its maximum in the fhght of the flying fish, 

 are all adaptations to escape specific attacks. Aside from these 

 general adaptations in the habit, structural adaptations against 

 fish-eating enemies are also found. 



The stickleback has divergent, erectile spines that can be locked 

 when erected. This arrangement is altruistic rather than egoistic. 

 While it does not prevent a duck or other animal from eating an 

 occasional stickleback the duck is not Ukely to be tempted by a 

 second stickleback. More effective weapons are the erectile dorsal 

 and pectoral spines of the catfishes. In the stone cats the spine 

 is surrounded by glandular tissue producing poison. The spine in 

 entering an opponent pierces the gland and carries some of the 

 poison into the wound. 



Color must be looked upon as an adjustment to light in the 

 presence of enemies. The amount of color on the surface of a 

 fish is proportionate to the intensity of the light in the environment. 

 The arrangement of the color is conditioned by the surroundings. 

 Its presence is an adaptation to the physical environment and its 

 arrangement is an adaptation to the biological environment. All 

 animals living for generations in caves become bleached and finally 

 lose all pigment. Nocturnal fishes are in large measure black. 

 Bottom fishes, like the darters, hog sucker, miller's-thumb, are 

 mottled and crossbarred. Weed-inhabiting species are barred (yel- 



