102 
less to its encouragement. The fishermen commonly regard these 
fishes as a mere nuisance, and leave them to die on the bank by | 
hundreds, rather than take the trouble to return them to the water. t 
They are a very delicate species, and are easily killed by rough © 
handling in the seine, but the, majority of those captured might be ~ 
saved with a little care. 4 
The abundance of these fishes as compared with some other spe-— 
cies 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. ‘I'wo or three items from my 
notes will furnish the basis for an intelligent estimate of this num-_— 
ber. 
From the stomach of a Stizostethium canadense caught in Peoria. 
Lake, October 27, 1878, I took ten well-preserved specimens of Dory-— 
soma, 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-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 men- 
tioned 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 can not reckon the average life of a Stizostethium — 
at less than three years, and it is probable nearly five. The smallest 
estimate we can reasonably make as 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 miles of river like the Illinois, would there-— 
fore 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 exceed 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 
predaceous fishes. Dorysoma, being a mud-eater and a vegetarian, | 
taking animal food only during the Entmostracan period, can pro- 
babry be more readily maintained in large numbers in our muddy 
streams than’ any other fish. a | 
It is evident that the increase of edible fishes without a corre- 
sponding supply of food will be largely time and labor thrown 
away. Probably if protected from wanton and ignorant destruction, - 
re Dorysoma would abound sufficiently, as it 1s enormously pro- 
ific. | 
The following table is similar to that given for the preceding 
family. The mark + is used to indicate the occurrence of an ele- 
ment in too small an amount to figure in the ratios: : 
ov 2M 
Ett oe 
