PRESIDENTIAL ADDRESS. 499 
a 
feeding ground of the Dogger Bank, and Garstang has been able to show 
that by carrying the young plaice in steamers and transplanting them at 
the proper time on to this rich feeding ground, their rate of growth can 
be greatly accelerated and thus their market value largely increased, just 
‘as Dr. Petersen has done in the case of plaice on Thisted Bredning. 
A few years ago there was no reliable method of determining the age of 
fish. Petersen’s method of arranging the measurements of a large number 
of specimens in a scale according to size, when they resolved themselves into 
certain groups, which were considered to coincide with age-classes, has been 
superseded by the discovery of Reibisch, Heincke, and others, that many 
of the bones, the scales, and the otoliths of fishes show annual age-rings, 
like those found in the trunk of a tree or in the horns of cattle. By 
laboriously counting the rings on the otoliths of thousands of plaice, 
Dr. Wallace and others have been able to determine their rate of growth, 
and to show that some specimens attain the age of twenty-five and even 
twenty-nine years. Similar investigations have shown that the sexes have 
a different rate of growth. The age at maturity is found to differ in 
different regions, but in the majority of cases Wallace found that the males 
are sexually mature (four to five years) a year before the female is capable 
of spawning (five to six years). We can now correlate age with size and 
with weight. 
The migrations of the plaice and of other fish and their rate of growth 
depend, amongst many other factors, upon their food supply. And the 
nature of the food of fishes has recently been re-investigated in the North 
Sea. I give some of Todd’s results, which were made by the examination 
of some thousands of fish of thirty-one species. Of these I select three— 
the cod, the plaice, and the dab. 
Percentages of stomachs containing various kinds of food 
Cod. 
Size of fish in cm., 0-15 15-30 30-60 60+ 
Pisces 5 on a ONPG 11 p.c. 52 p.c. 67 p.c. 
Mollusca . nO 2 16 4 
Crustacea . . 100 95 67 3 
Polychaeta xO 9 9 26 
Plaice 
Size of fishincm.. 0-10 10-20 20-380 80+ 
Pisces ‘ » _O0'p.c; 1 p.c. 5 p.c. 5 p.c. 
Mollusca . a he 66. 76 84 
Crustacea , 2 eB, 16 13 1L 
Polychaeta Aes) 37 51 42 
Echinoderma . 0 20 13 6 
Dabs 
Size of fishincm.. 0-10 10-20 20-380 30+ 
Coelenterata . Ope. 18 p.c. 18 p.c. 20 p.C. 
Echinoderma . 0O 26 25 2 
Polychaeta » 30 22 20 10 
Crustacea . 2 70 30 SD 61 
Mollusea . pares 48 57 65 
These tables show what, of course, was more or less known before, that 
as a rule the young fry live very largely, and in many cases solely, on 
crustacea. To a great extent the supply of suitable food dominates the 
movement of the young fry, for nowhere is the truth of the Frenchman’s 
definition of life, ‘I eat, thou eatest, he eats,’ with its terrible correlative, 
‘IT am eaten, thou art eaten, he is eaten,’ more true than in the sea. Later 
in life the fishes’ taste alters, and with increased size they can ries 
, r KK 
