4 
fauna. He is of the opinion, that this condition can be explained in this way, 
that new plankton often, almost daily in fact, is carried by the current into the 
Canal, and that what is present is eaten up hy the bottom-animals; I think, that 
the condition can be explained in a much more natural manner from the large 
deposits of detritus. (See Brandt: Wiss. Meeres. IV. Bd. Kiel. 1899, p. 226, Note 
and Mitt. Deutsch. Seefischerei v. 1897, pg. 232—241). 
At many places in the salt-water it is naturally more difficult to obtain 
information regarding the importance of the plankton in quantitative regards for 
the food of the fauna, than in freshwater, as the latter is sometimes quite 
enclosed; but the results obtained hitherto do not seem to indicate that the 
plankton plays any great role in the food question of the fishes. Wesenberg- 
Lund writes in »Ymer« 1909, (Part I, pp. 132—133) as follows: »With regard to 
fishery questions it has hardly been made clear, that the plankton does not play 
nearly so important a part for the useful fishes of the freshwater as for those of 
"the sea. Not a single one of the former lives as adult on plankton. — Even if 
we might say that the young live partially on plankton, this description of the 
food of the young is on the whole erroneous. Its food should much rather be 
called the lower animal and plant world of the littoral zone —.« 
In the recently published Nr. 1 of the »Deutsche Fischerei-Zeitung« 1911 
B. Schiemenz states (p. 2): »dass der Auftrieb (Plankton) nur fir wenige Fische 
als Hauptnahrung in Betracht kommt, dass aber die meisten unserer Sisswasser- 
fische und auch unsere såmmtlichen Teichfische sich von der Ufer- und Boden- 
fauna ernåhren und der Auftrieb (Plankton) nur als Gelegenheits: oder Notnahrung 
in Betracht kommt — —«. He shows further, how the word plankton in regard 
to freshwater has been misused and gradually come to include everything that 
occurs on occasion in the water, even the organisms which really belong to the 
bottom; we should return to Hensen's definition of the plankton, he says. Ås 
contrast he uses the word »Aufwuchs«, by which he understands: »diejenigen 
Organismen, die auf den Pflanzen und andere Gegenstånden des Ufers and flachen 
Wassers wachsen und sich herumtreiben.« » Dieser Aufwuchs ist es nun, der sehr 
wesentlich als Fischnahbrung in Betracht kommt.« 
These are the opinions of men who have studied the biology of our fresh- 
waters for many years; for a long time many seem to have overestimated the 
importance of the plankton as a source of food, and I am inclined to believe, that 
at least the same has been done in the case of our coastal seas. 
I shall not seek to penetrate deeply on this occasion into what is known 
regarding the metabolism of the freshwater, as I have not made investigations in 
this field: but a study of recent literature, E. Walter, Sehiemenz, Zuntz, 
Knauthe, Knørrich etc., seems to me to indicate definitely, that even if dis- 
agreement exists as to what should be called plankton and what not — a dis- 
agreement which has perhaps tended to accentuate the differences of opinion — 
— yet all are agreed, that the dissolved and suspended, organic materials 
in the water as well as the detritus on the bottom coming from dead 
bottom-plants, are of great importance as food for the animals. (Schie- 
menz: Anhang pp. 200—201 in Max. von dem Borne: Kiinstliche Fischzucht, 
bte Ausgabe 1905, and E. Walter: Die Karpfennutzung in kleinen Teichen, 1909, 
