of the Fishery Board for Scotland. 
191 
in the very early stages of the species producing pelagic ova — that is 
almost all the food-fishes — is comparatively immense. The Rev. Mr Green, 
Inspector of Irish Fisheries, found by experiment that minute Crustacea, 
which swarm in the surface waters, devour pelagic ova ;* and Mr Scott 
has discovered that Sagitta, which exists in immense multitudes, preys 
upon larval fishes. That protection of the ovum alone is a most import- 
ant factor is also indicated by the extremely low fecundity of the pipe- 
fish (Syngnathus). 
But there is evidence from the life-history of Zoarces that the great 
destruction at all events occurs very early. Mr Jameson has made a 
series of careful observations at Dunbar, as to the number and sizes of the 
young of this viviparous fish, the size of the parent, and the rate of 
growth of the young. Of a large number of females, varying from about 
seven to 16 inches, the mean number of young was 65, the range being 
from twenty to over a hundred. Twenty-two specimens from a group 
of sixty-three, ranging in size from 38 mm. to 53 mm., and born 
on 8th January, were placed in a vessel of water, and have been reared 
since. On the 11th June their length ranged from 59 to 89 mm., the 
mean being 74 mm. Thus, in five months they had increased their 
length by from 21 to 36 mm. Comparison was made from time to time 
with young Zoarces caught in the sea, and it shows that those in cap- 
tivity, which were supplied abundantly with food, were of a larger size. 
It is evident from these facts that Zoarces is far removed from sexual 
maturity during the first year, and probably does not reach it till the 
third year of its life, the period at which it is believed the cod first comes 
to maturity. Now the importance of these observations lies in this, that 
40 or 50 of the progeny of a sea-fish, which becomes mature probably only 
in the third year of its life, are sufficient for the maintenance of the 
species ; and assuming that, for example, the cod reaches maturity about 
the same epoch, and that there is no exceptional destruction after its 
young have reached a similar stage, the inference is permissible that of 
the 5,000,000 or 6,000,000 ova produced by a female cod, less than 100 
survive to attain a length of two inches or so. In the light of the im- 
portant observations of Dannevig on the rate of growth, it may be said 
that by placing some fifty of these young cod, between two and three 
months old, on the fishing ground, one adult cod will be available as a 
source of food supply. 
Pisciculture, or the protection of the young, may cease when different 
stages have been reached: (1) it may be extended only to the ovum; 
(2) to the larval fish until the yolk is nearly absorbed ; (3) the young 
fish may be reared to a certain size. The practice in sea-fish culture 
hitherto has been mainly to limit protection to the ovum, i.e., to the 
period anterior to hatching — the newly hatched fry being then placed on 
the fishing ground. The protection during the first few weeks, when the 
ratio of destruction under natural conditions is exceedingly great, must be 
beneficial in equal ratio — but the amount of this benefit cannot be at present 
expressed numerically with any approach to exactitude. There is little 
doubt that the extension of protection until the yolk is about absorbed, 
when the young fish has to depend on external sources for its nourishment, 
would be of the greatest value. But for this purpose it is essential that 
large enclosures of sea-water should be available. After the absorption 
of the yolk there is a difficulty in providing suitable food for the young- 
fish, and in sufficient abundance. This can be done also by means of 
* It is possible that the comparatively small fecundity of the halibut and long 
rough dab is accounted for by the unusually large size of the ova which will prevent 
their being swallowed by hosts of minute Crustacea, &c, 
