9 
different physically and biologically from either of the other three, 
is not beyond our reach, and comparative studies of all these streams 
have been begun by us this year.* 
In such an investigation as is here proposed, the foundation in¬ 
quiry which must fix our beginning' points and show where the prin¬ 
cipal emphasis should at first be placed, is this: Just what is it that 
we need to know in order that we may be in a position to do all 
that we might hope to accomplish, and ought to undertake, for the 
conservation and increase of our aquatic resources? To this in¬ 
quiry I must make, at first, a general and perhaps a disappointing 
answer. It is perfectly evident that if we wish to maintain or to 
improve the conditions of life for the fishes of our rivers, we must 
first know what the present conditions are, and which of these are 
the most important to our purpose. We might, it is true, hatch 
young fish by the million, and throw them out by the hundred thou¬ 
sand, into all the sorts of waters which their species inhabit, without 
any precise knowledge on cur part of the conditions in which they 
will find themselves when set free, or any rational judgment of the 
chance that they can survive to adult size. This sort of thing, 1 
surmise, has sometimes been done, but I hope that it is, at any rate, 
done no longer, and certainly it can no longer be defended as either 
scientific or practical; it is simply ignorant. Intelligent plans for 
their improvement require that we should know the conditions under 
which our fishes live, and that we should be able to distinguish bene¬ 
ficial conditions from injurious, and important conditions from un¬ 
important. We need to know what our fishes require in respect to 
the main essentials of their well-being—that is, to a suitable water 
supply, to oxygen for respiration, to temperature in the different parts 
of the year, to their food at all their ages, to breeding places, to 
freedom of migration and other necessary movements to and fro, and 
to freedom from injurious physical conditions, from poisonous gases 
and solutions, from parasites, from diseases, from excessive com¬ 
petition, especially for food, and from decimation by their enemies 
It is commonly conceded I think, both by scientific students and 
by practical fishermen, that the most general and rigorous limita¬ 
tions upon the numbers of fishes are those set by their breeding 
*Plankton collections, continuous for all practical purposes, have now been 
made from the main streams of these great rivers, aggregating - 1010 miles for 
the Illinois, 1195 miles for the Mississippi, and 46 miles for the Ohio. On the 
Illinois river these collections were made, for ninety miles, from the station 
launch; but for the remainder of this Illinois work, and for all that on the Mis¬ 
sissippi and the Ohio, we have had the use of the steamer “Illinois,” kindly 
placed at our disposal for this purpose by the State Fish Commission. 
