62 ILLINOIS BIOLOGICAL MONOGRAPHS [62 



THE BROOK SILVERSIDES LABIDESTHES SICCULUS (COPE) 



INTRODUCTION AND DESCRIPTION 



The brook silversides, Labidesthes sicculus (Cope), which in southern 

 Wisconsin is characteristically not a brook species at all, being found most 

 commonly in clear water lakes, is one of the most abundant and typical 

 species of lake minnows found in Waukesha county. While its abundance 

 varies considerably in the different lakes, yet it has been found in all of the 

 lakes of considerable size (28 in number, table 4) and is conspicuously 

 absent from the small, muddy-bottomed ponds, and from all lakes and 

 rivers whatsoever their size in which the water is not clear. 



This little species is the only Wisconsin representative of the family 

 Atherinidae of Linnaeus (1758). These fish, known generally as the 

 "friars" or "silversides" compose a family whose members are typically 

 salt water forms. The family is composed of sixteen genera and about 

 seventy species, none of which attains a large size. Among the more 

 familiar genera can be listed Atherina, the friars; Chirostoma Swainson; 

 Menidia (Bonaparte) Jordan and Gilbert; Atherinopsis Girard; Atherin- 

 opus Steindachner; and Labidesthes Cope. Of these genera, Menidia is the 

 closest to Labidesthes both in morphological characters and in general 

 habits, as Menidia, typically a marine genus, often ascends streams and 

 rivers, passing from the brackish water environment to the fresh water 

 conditions beyond the tidal zone. Structurally Labidesthes differs from 

 Menidia in the prolongation and depression of both jaws to form a "beak" 

 which characteristic gives the name to the genus — "a pair of forceps." 

 The name is well chosen, and gives a clear picture of the daintiness of the 

 mouth structure. The Atherinidae are all carnivorous in their habits and 

 in common all the species have a straight gut lacking entirely pyloric 

 ceca. The small size of the individuals makes them of little economic 

 importance as food fishes but those which reach a size sufficiently large to 

 warrant attention are highly valued as food, hence the common name of 

 some of the marine species: "Pez del Rey" — fishes of the king! This applies 

 particularly to the genus Menidia, and more especially to Menidia sardina. 



The genus Labidesthes was created by Cope in 1870 to hold the type 

 species, sicculum, originally described by himself as Chirostoma sicculum 

 in 1865, the type specimen coming from the region of Grosse Isle in the 

 Detroit river. This places the type locality as the inlet of the Detroit river 

 into Lake Erie, some twelve miles south of Detroit, Michigan. The genus 

 comprises a single species, of which the following description is given by 



