65 
The results from Sallingsund and Thisted Bredning seem to me sufficiently 
clear; the digestive tract is emptied of its contents before 4—5 a. m. and is again 
filled in the course of the forenoon; in Nissum Bredning on the other hand the 
morning investigation at 4—6 a. m. shows a little in the gut and stomach; this 
suggests a longer time for digestion in this Bredning, where the plaice thrive very 
badly (cf. Franz for the North Sea). Whether the plaice digest much in the 
course of the day, is not known; but what is found in the digestive tract, 
when it is full, is digested in the course of the day at any rate in Sallingsund 
and Thisted Bredning; this is therefore its minimum of food at this time of 
the year. 
To ascertain something about the mass of this minimum, the amount of 
dry matter in the stomach-contents of 6 kg. of plaice from Thisted and Nissum 
Bredning was investigated, partly taken when they contained least, partly when 
they had most food; but as it is impossible to separate out the Lammellibranch 
shells in the finely divided contents of the stomach, Boysen Jensen determined 
the amount of carbon in these; when the results are multiplied by 2, we may 
assume that we are near the actual quantity of dry matter in the contents of the 
stomachs; but larger or smaller parts of the food there must be considered to have 
been digested and absorbed. 
organic dry matter 
Thisted Bredning, ?%/, 1910. 4—5 a. m. 6 kg., 22 spec. 3.42 gm. 
— EEN OTTE) Fam ORK RODES peer 18 gm. 
Nissum Bredning, ?%/, 1910. 4—6 a. m. 6 kg., 65 spec. 4.4 gm. 
— —  , ?5/, 1910. 9—11 a. m. 6 kg., 57 spec. 8.4 gm. 
I believe that we get nearest to the real conditions for Thisted Bredning, 
if we assume that the plaice digest daily at least as much as they have at any 
one time in their digestive tract; thus, the 19 plaice consume ca. 18 gm. daily, 
or almost a gram for each, which means 10 gm. raw matter daily or 3 gm. dry 
matter per kg. daily. As about 100,000 kg. of plaice was fished in Thisted Bred- 
ning in 1910, the amount they have eaten, provided that they eat just as much 
from April to November or 240 days of the year, would be 72,000 kg. This esti- 
mate however is probably too high, as the plaice are small in the beginning and 
only later eat much, especially in August to November. 
As already mentioned we know approximately the number of plaice which 
live each year in the Bredning; almost all in fact are transplanted and by far the 
greater part are fished up each year before Christmas. Here, therefore, we are 
dealing with a yearly growth and the conditions are thus much simpler than they 
usually are in the sea. It is different on the other hand with the eel; we only 
know roughly how many are fished yearly, but I imagine that a very large number 
migrate out as silver eels without being fished in the Bredning; further there are 
at least 6—8 younger age-groups which are yet too small to be caught. In this 
case a calculation of what the quantity of eels fished has eaten in a year, is far 
from giving the amount annually devoured by all the eels; it is evident, therefore, 
that one kg. of eels is much dearer to produce than one kg. of plaice, even if 
we presuppose that both eat about the same amount per kg. per annum and grow 
to an equal extent. 
9 
