1056 FRESH-WATER BIOLOGY 



and consists of the organisms composing the plankton, largely 

 Entomostraca. The members of a local fish fauna are distrib- 

 uted in the following ecological groups: pelagic, littoral (bottom 

 fishes, all predacious fishes), and nocturnal. 



To these should be added abysmal fishes, but nothing is known 

 of these in America except that Triglopsis is found in deeper water 

 of the Great Lakes. 



Pelagic, abysmal, littoral, and nocturnal forms are such as find 

 their food in those regions or times. Their adaptations are but 

 secondary adjustments to the region in which their food is found. 

 Everything eatable is food for some fishes though few have such 

 omnivorous tastes as to take the entire bill of fare. The skipjack 

 {Lapidestes) is a surface ranger and occupies as definite a position 

 under the surface of the pelagic area of our lakes as the swallows 

 do over it. Insects and all other minute terrestrial organic mat- 

 ters reaching the surface of the water find a lodgment in their 

 stomachs. Frequently the fish darts out of the water as the 

 swallow dips into it to secure its food. Its food is not confined to 

 terrestrial strays, but it also takes Entomostraca and Chironomus 

 larvae. Zygonectes and Fundulus also range near the surface but 

 nearer the shores. In the mountain lakes in which the skipjack 

 is not found, the half-grown whitefish (Coregonus williamsoni) occu- 

 pies the same ecological niche. In Lake Tahoe on June evenings 

 individuals nine inches long rise to gnats blown into the lake, and 

 they can then be caught with a minute hook baited with a fly. 



In the American tropics a killifish with half its eyes adapted to 

 seeing in air and the other half adapted to seeing in water also 

 ranges on the surface. Larger objects reaching the surface of the 

 water are secured by black bass, trout, and other fishes that range 

 and poise in deeper water and ''rise" to their prey near the sur- 

 face as the kingfisher dives for his. All fishes that rise to arti- 

 ficial bait, grasshoppers, etc., belong to this group. Some trout 

 rise more readily to a mouse but for esthetic reasons this cannot be 

 recommended for bait. 



Another series of pelagic fishes is formed by the plankton feeders. 

 There are several sorts of these. The young of most fishes, the 

 sunfishes and minnows and some whitefishes, see their minute 



