416 1, dg ZMBIL ADIN 
numbered labels and liberated. The transplantation was carried out in 
May, and during the following year large numbers of the marked fishes 
were returned by the fishermen. The amount of growth shown by the 
followmg autumn and winter was very remarkable. Small, under-sized 
fish of little or no market value had become fine Plaice, of good size and 
in excellent condition. The preceding diagram (Fig. 6) shows the growth 
of these transplanted fish, compared with the growth of fish of the same 
size which had remained on the inshore grounds. Taking the figures for, 
say, the following January, whereas the average length of the trans- 
planted fish was I] cm. the size of those left on the Horn Reef ground 
was about 5-5 cm. 
If instead of considering the length of the fish we take the percentage 
increase of weight the result 1s even more striking. Whereas by the follow- 
ing spring the fish that remained on the Danish Horn Reef ground had 
increased in weight by 1060 per cent., that is to say, had doubled their 
weight, those put out on the Dogger had increased their weight by 400 
per cent.,; that is to say, they were five times as heavy as they were 
originally, 
Since well-grown Plaice command a much higher price per lb. than 
small ones this increase of weight means that the value has increased 
to perhaps seven times the original value. 
These results of investigations on the age of Plaice and their rate of 
growth have several important practical aspects, apart from the sugges- 
tion of a direct improvement of the fishery by the transplantation of 
young fish from crowded nursery grounds to rich feeding grounds such as 
the Dogger Bank, where the rate of growth is much more rapid. It would 
seem that the most profitable fishery would result from concentrating 
the fishing as much as possible on Plaice of the Age Groups IV, V and VI, 
that is to say, on fish in the fifth, sixth and seventh years of their life. 
Before this they are small, but capable of rapid growth and rapid increase 
in value. After the seventh year the growth gets slower, and as long as 
a sufficient supply of mature fish is allowed to remain to ensure an ade- 
quate amount of spawn for the perpetuation of the race, it would appear 
that from a commercial point of view it is of greater advantage to put 
the seven year olds on the market rather than to allow them to remain 
in the sea. They would increase in value very little compared with the 
amount of nourishment they would consume, whilst when they are re- 
moved the food they would have eaten becomes available for the younger 
fishes, which grow in size and value at a much more rapid rate. 
In this connection the age at which the majority of Plaice mature for 
the first time is important. According to Wallace (24, p. 40) for female 
Plaice this ‘“‘ age of first maturity ” in the Southern North Sea is five 
