10 Part L11.—Twenty-first Annual Report 
much scarcer on the deep-water grounds than inshore. The 
absence or great rarity of the young forms of some other species, 
as the saithe or coal-fish, the hake, pollack,and ling, in the latter area, 
while they are known to be common in many cases near land, also 
indicates an extensive wandering. An inshore winter migration of 
cat-fish was also established. The results generally tend to show 
that the extent of the migratory movements of even such relatively 
sedentary forms as flat-fishes is much greater than has been 
commonly supposed, and that the predatory round-fishes may 
traverse great distances. They suggest, moreover, that by extended 
observations of the kind, whether on board fishing vessels or the 
steamers engaged in the International Survey, it would be possible 
within a limited time to prepare charts showing with considerable 
accuracy the extent of the distribution and of the wanderings of 
all the bottom fishes in the North Sea and adjoining areas, as well 
as the facts relating to the place and period of spawning. 
THE HATCHING AND REARING OF Foop FISHES. 
During the hatching season in 1902 the number of fertilised eges 
of the plaice obtained from the spawning pond was 72,410,000, or 
about seven millions more than in the previous year, and 29,120,000 
more than in 1900. The number of fry which were hatched and 
retained in the apparatus until approaching the post-larval stage 
amounted to 55,700,000, and these were liberated off the coast of 
Aberdeenshire and in Loch Fyne. At the end of the previous 
season the number of adult plaice in the pond in good condition 
was 767, most of which continued to thrive during the summer and 
autumn. To these, others, obtained from the vessels engaged in the 
trawling investigations, were added later, bringing the breeding- 
stock up to about one thousand plaice of both sexes. 
In the latter part of January the temperature of the water in 
the spawning-pond was rather lower than usual, and few eggs were 
observed to have been shed until the early part of February. The 
first collection was made on the 8th of that month, and after a 
check in the spawning due to a severe frost, when the temperature 
of the water sank to freezing-point, the number of eggs gradually 
increased until in the first half of March more than two millions, 
and occasionally nearly three millions, were taken from the pond 
daily. Thereafter the number diminished, and the last collection 
was made on the 25th April. 
The considerable increase in the productiveness of the hatchery 
in recent years is due to the more ample and suitable arrange- 
ments existing at the Bay of Nigg, and particularly the provision 
of a large tidal spawning pond, in which a good breeding stock can 
be maintained throughout the year. The natural conditions and 
facilities for the work, and the abundant supply of sea-water of 
good density and purity, have also assisted in the result. At the 
same time the expense has been reduced, largely owing to the 
supply of watcr to the tank being tidal, whereby the need of 
pumping is greatly diminished, and the combination of the hatchery 
