67 
it by way of calculation, as it is difficult to determine, how much is produced 
annually of plaice-food per m.?”; direct practical experiments with transplantation 
of more and more plaice per hectare will however lead to the goal, namely, slower 
growth; but it will only be by means of similar studies to the present, 
carried out at the same time, that we shall learn whether this slow 
growth is really due to the insufficient quantity of the food-animals or 
possibly to other causes. It is remarkable, that the plaice in Nissum Bredning 
do not eat up everything there; as it seems to me that they must always be 
hungry. The reason is possibly, that they cannot find all the animals which might 
serve them as food. 
In Nissum Bredning the plaice in 1910 were feeding especially on Nucula 
and Macoma baltica, Abra, Mactra, Philine, Pectinaria and worms, as also more 
rarely Corbula, Solen, Acera, Idothea and Ophioglypha. 
Comparing the quantity of the animals the plaice eats, in both Bredninger, 
we obtain for Thisted Bredning, excluding Mya: 
1910. Spring 19.03' gm. Autumn 24.00 gm. per 10 m.? 
For Nissum Bredning: 
1910. Spring 7.49 gm. Autumn 13.40 gm. per 10 m.? 
The increment from spring to autumn is due in Thisted Bredning mainly 
to Abra alba, in Nissum Bredning on the other hand to Nucula, Pectinaria and 
Aplhrodite. At all times of the year, therefore, there is more plaice-food per m.? 
in Thisted Bredning than in Nissum Bredning. At certain times the plaice in 
Nissum Bredning mainly contained Macoma baltica (April), Nucula (May), Abra alba 
and mtida (August) and Philine (October); but both Solen and Mya are seldom 
there and these two with Abra are certainly the choicest Lamellibranchs of the 
.plaice in the Limfjord; that the quantity of Abra does not increase here more than 
from 0.23—3.0 gm. must certainly be ascribed to the enormous amount it is sought 
after. The increase of Nucula in the autumn is perhaps due to the fact, that the 
plaice does not seem to be specially fond of this Lamellibranch, which is evidently 
»heavy on the stomach«, often closed and unbroken. In the spring however many 
are devoured in Nissum Bredning. It seems therefore, that the quantities of dry 
matter, ca. 30 gm. per 10 m.?, the eel and plaice digest in Thisted Bredning, do 
not mean much by comparison with the great production of up towards 200 gm. 
per 10 m.? of the lower animals here; but there is a great difficulty just in this 
Bredning in determining, what quantities of animals are at the diposal of 
the fishes, this namely, that only a portion of the quantities of Mya truncata 
is eaten by them; some are too large for them to swallow. To determine 
which are smal! enough to serve as fish-food, is not easy, as it seems that both 
the eel and the plaice can bite off the siphons of the larger Mya and thus obtain 
a portion of the larger animals. As the quantity of Mya is so greatly in excess of all 
others, this fact leaves a big margin in the determination of the available quantity 
of fish-food. Many Mya are eaten, especially the smaller at any rate of up to 2—3 
cm. length of shell; this Mollusc is at times extremely common in the stomachs 
of plaice both in Thisted Bredning and at several other places im the Limfjord 
(Livø Bredning several places, Risgaard, Hvalpsund and Skive); but not in Salling- 
sund, Kaas and the western reaches, where large Mya is to be considered as a 
