36 
The Food of Fishes. 
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-pre- 
served specimens of Dorysoma, each from three to four 
inches long; and from a Stizostethium vitreum 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- 
tperch. 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; but, 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 cannot reckon the average life of a Stizo- 
stethiura at less than three years, and it is probably near- 
er five. The smallest estimate we can reasonably make as 
to the food of each pike-perch would therefore be some- 
where between eighteen hundred and three thousand 
fishes like Dorysoma. A hundred pike-perch, such as 
should be taken each year along a few miles of a river 
like the Illinois, would therefore require one hundred 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 ex- 
ceed the mere surplus reproduced — otherwise the species 
would be extinguished — we can form some approximate 
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 entomostraean 
