120 Part III.—Twenty-third Annual Report 
IV.—REPORT ON THE OPERATIONS AT THE MARINE 
HATCHERY, BAY OF NIGG, ABERDEEN, IN 1904. By 
Dr. T. Wemyss Fuuron, F.R.S.E., Superintendent of Scientific 
Investigations. 
During the season of 1904 the operations at the Marine Hatchery 
were continued in connection with the hatching of the eggs of the plaice, 
as in previous years, and a number of lobsters were also dealt with. 
The hatching apparatus and the various ponds in connection with the 
establishment continue to perform the work for which they were 
intended in a satisfactory manner. An account of these and of the 
methods employed in the collection of the eggs and their treatment in 
the hatchery has been given in some of the previous reports, to which 
reference may be made for the detailed description. 
It need only be said here that the adult fishes which act as the brood 
stock are confined throughout the year in a large tidal pond, where 
they are regularly fed, almost entirely with common mussels, and that 
at the spawning-time the fertilised eggs, shed freely into the water, are 
collected daily, or almost daily, by means of a large net of mosquito 
netting, and are then transferred to the incubating apparatus in the 
hatchery. 
The duration of the period of development, until hatching takes 
place, varies according to the temperature of the water at the time; 
the period is longer at the beginning of the spawning season, when the 
temperature is low, than towards the end of the season, when the 
temperature has risen considerably. At the beginning of the work in 
January the average time of incubation before the eggs hatch is about 
three weeks, while at the end of the season they hatch in about a fort- 
night. The larval fishes, after they are hatched from the eggs, are 
kept in the apparatus for several days until the yolk-sac is partly 
absorbed, and they are then transferred to the sea in appropriate ap- 
paratus. Experience has shown that the best results are got by 
liberating the fry before the yolk has been quite used up, and when 
they are able to feed for themselves. 
It is calculated that, taking the two periods together—the time of 
incubation and the period referred to after hatching—the eggs and 
larvee are protected in the apparatus for about half of the time from the 
spawning of the eggs to the transformation of the post-larval fish, 2.e. 
to the adoption of the adult form and habit, after which, owing to the 
protection afforded by concealment in the sand, the natural mortality 
is, relatively speaking, small. 
In the season of 1904 the floating eggs were first observed in the 
water of the spawning pond about the middle of January, but they 
were few in numbers. The first collection was made on the 26th of 
that month, about the same date, that is, as in the preceding year. 
The last collection was made on the 29th April, or more than a fort- 
night earlier than in 1903. This is probably partly accounted for by 
the greater relative intensity of the spawning in the earlier part of the 
season in 1904, but it is also, no doubt, connected with the fact that 
