36 The Fond of Fishes. 



other species in the river might seem to indicate that they 

 are common enough as it is. Few realize, however, the 

 number of fishes needed to feed a pike-perch to maturity. 

 Two or three items from my notes will furnish the basis for 

 an intelligent estimate of this number. 



From the stomach of a Stizostethium canadense caught 

 in Peoria Lake October 27, 1878, I took ten well-preserved 

 specimens of Dorysoma., each from three to four inches 

 long ; and from a Stizostethium vitreuni I took seven of 

 the same species, none under four inches in length. As 

 the Dorysoma is a very thin, high fish, with a serrate belly, 

 these were as large as a pike-perch can well swallow ; and we 

 may safely suppose that not less than five of this species 

 would make a full meal for the pike-perch. The species 

 is a very active hunter, and it is not at all probable that 

 one can live and thrive on less than three such meals a 

 week. The specimens above mentioned were taken in 

 cold autumn weather, when most other fishes were eating 

 but little ; l)ut, since fishes generally take relatively little 

 food in winter, we will suppose that the pike-perch eats, 

 during the year, on an average, at this rate per week for 

 forty weeks, giving us a total per annum of six "hundred 

 Dorysomas destroyed by one pike-perch. We can not reckon 

 the average life of a Stizostethium at less than three years, 

 and it is probably nearer five. The smallest estimate we 

 can reasonably make as to the food of each pike-perch would 

 therefore be somewhere between eighteen hundred and 

 three thousand fishes like Dorysoma. A hundred pike- 

 perch, such as should be taken each year along a few mile's 

 of a river like the Illinois, would therefore require one hun- 

 dred and eighty thousand to three hundred thousand fishes 

 for their food. Finally, when we take into account that 

 a number of other species also prey upon Dorysoma, and 

 that the whole number destroyed in all ways must not 

 exceed the mere surplus reproduced, — otherwise the spe- 

 cies would be extinguished, — we can form some approxi- 

 mate idea of the multitudes in which the food species must 

 abound if we would support any great number of preda- 

 ceous fishes. Dorysoma, being a mud-eater and a vegeta- 

 rian, taking animal food only during the entomostracan 



