246 BULLETIN OF THE BUREAU OF FISHERIES. 



within these patches. In this they differ from the rock bass, the small-mouthed bass, and 

 the bullhead, which have been taken only in or near vegetation and in shallow water, 

 although their size would apparently enable them to enter the deep-water community. 

 In addition to the five species listed, one other, the cisco, or lake herring, must 

 occur at some level considerably above the bottom. This may be inferred from the 

 fact that it has never been taken by us in fine-meshed gill nets set on the bottom in 

 either shallow or deep water. It is probable that it should be regarded as a member of 

 a nekton community characteristic of a mid-water habitat. No other fishes are known 

 to be associated with it. 



RELATION OF DOUGLAS LAKE SPECIES TO THOSE OF OTHER WATERS. 



Douglas Lake has large areas of bare sand or gravel bottom, comparatively clear 

 water, kept well agitated by the wind, and a relatively sparse growth of vegetation. 

 It would be of interest to learn: (i) Whether its fishes give preference in other regions 

 to the conditions that they find in Douglas Lake, and (2) whether their distribution 

 over the continent is such as to afford these conditions. Forbes and Richardson (1908) 

 give the only data known to me on the habitat preferences of American fresh-water 

 fishes. For many species they indicate by coefficients or percentages the kind of water 

 preferred (whether large rivers, small rivers, creeks, lakes, or ponds), the kind of bot- 

 tom (mud, rock and sand, mud and sand), and the amount of current (swift to mod- 

 erate, slow to stagnant, variable). I am unable to interpret these data in such a way 

 as to make them available for a detailed comparison of the habitat preferences of the 

 fishes of Douglas Lake with those of Illinois, and therefore restrict myself to noting 

 two points : 



There is no mud bottom in Douglas Lake, none at least in its shallower parts. 

 The bottom is sand or gravel, with an overlying stratum of muck in the deeper water 

 and in protected situations in shallow water. None of the species occurring in the 

 lake are among those given by Forbes and Richardson as preferring mud bottom in 

 other waters, and but two species {Ameiurus nebulosus, and Umbra limi) are commonly 

 found on such bottom in other waters. The other Douglas Lake species, in so far as 

 their preferences are indicated for Illinois, are found with greatest frequency on a 

 bottom which includes rock or sand or both. 



Among the fishes in our list the following are found by Forbes and Richardson 

 to show a preference for small rivers or creeks: Catostomus commersonii, Semotilus 

 atromaculatus, Notropis cornutus, Ambloplites rupestris, Microplerus dolomieu, Percina 

 caprodes, Boleosoma nigrum. Suckers, rock bass, and small-mouthed bass occur often 

 in lakes, but the homed dace and the common shiner are rare in lakes. Forbes and 

 Richardson give the water preference of the horned dace as large rivers 1.67, creeks 

 3.77, lowland lakes o.ii. The species is of local occurrence in Douglas Lake and is 

 possibly introduced. For the common shiner the Illinois preferences are large rivers 

 o.ii, small rivers 2.45, creeks 3.00, lowland lakes 0.02, upland lakes 0.20. The species 

 is one of the most widely distributed and abundant of the Douglas Lake fishes. Its 

 abundance, together with the presence of the other species showing preference for small 

 rivers and creeks, indicates that in the character of its bottom, the movement of its 

 waters and the sparseness of its vegetation Douglas Lake affords the small-river-creek 

 conditions preferred by these species. 



