PROGRESS IN BIOLOGICAL INQUIRIES, 1926 671 
Rivers. Above Minneapolis, 1,500 to 2,000 wall-eyed pike were taken in one 
seine haul. No seining was done in the Chippewa River or in the Mississippi 
River at the foot of Lake Pepin and at Winona, but the game wardens at 
these places reported that game fish were abundant. 
No seine hauls were made in the Mississippi River just below Minneapolis, 
but the data on dissolved oxygen and bottom fauna make it seem very doubtful 
that any fish could exist there. Thirteen seine hauls made in the Mississippi 
River between St. Paul and Prescott yielded nothing except one stickleback. 
This was taken a short distance below the mouth of the Minnesota River. 
The absence of fish is correlated with the presence of tolerant or pollutional 
bottom-dwelling animals and low concentrations of dissolved oxygen. 'Thomp- 
son, who worked on the oxygen requirements of fishes in the Lllinois River, 
cluims that even two parts per million of dissolved oxygen are not sufficient 
to support fish life. The results of oxygen determinations that I have men- 
tion are far below two parts per million. 
I give below a table to show the relationship between the amount of dissolved 
oxygen, average number of fish per seine haul, and the number of species at 
stations 1 to 8. 



l l | 
Station | 12h | Leelee | Bower ereteaz | 8 
= = 13. 5S Fee | } | | a 
Parts per million of dissolved oxygen_______..______- | 6.59 | 6.08 | E 0. 67 | b Guy | 0. 87 | 0.51 | 0.39 | 7.10 
Average number of fish per seine haul._----_-------- 1, 009 750 | tee. | 6 0 0| 330 
Nem beri ofispecies ees ak es ahs 10. (Reet | oe ho Jo 0 | 17 
| | 


NotE.—Stations 5, 6, and 7 include all hauls (13 in number) made in the Mississippi River between St, 
Paul and Prescott. Station 1 is above Minneapolis, 2 is just within the metropolitan area, 3 just below 
Minneapolis, 4 is on the Minnesota River, and 8 on the St. Croix River. 
The results of the survey, which I have presented here very briefly, seem to 
point to the conclusion that the absence of fish in the upper Mississippi River 
from below the Twin Cities to Prescott is due to the pollution caused by 
dumping sewage from the Twin Cities into the river. 
AQUICULTURE 
GENERAL REVIEW—PATHOLOGY AND EXPERIMENTAL FISH CULTURE 
By Dr. H. S. Davis 
The problems that have been under discussion at this conference, with few 
exceptions, have been confined to the so-called commercial fishes. To my mind, 
the game fishes are in many ways fully as important as those that form the 
basis of the extensive marine and fresh-water fisheries. True, from the 
monetary standpoint they are not to be compared with the more abundant 
commercial species, but the importance of the game fishes in connection with 
the life and health of the Nation far transcends their market value. In evaluat- 
ing the relative importance of these fishes, statistics are of little avail. In the 
first place, we have very few statistics on the catch of the game fishes; and 
even if we had, they would be of little value as a criterion of their relative 
importance. Can you place a monetary value on the dozen trout or the couple 
of fine bass that are the concrete rewards of a day spent on a woodland stream 
or the more open waters of a beautiful lake? 
Not only do the standards by which we must gauge the relative importance 
of these fishes differ, but the scientific problems they present are in many 
eases quite different from those that characterize the commercial fishes. 
Inasmuch as the game fishes are predominantly fishes of our inland streams 
and smaller lakes, they are more susceptible to the influence of man, either 
for good or ill. Anyone who goes angling for trout or bass in these degenerate 
days does not require a knowledge of statistical methods to determine that the 
fisheries are depleted and that overfishing is a fact and not a theory. There 
is no doubt that the situation in many localities is a most critical one; and 
while the causes are fairly well understood, it may not be easy, in any particular 
instance, to lay one’s finger on the most important factor involved in the 
depletion. But it is not my purpose to consider the causes of this depletion, 
