404 GarsUmg : The Disappearance of the Plaice. 



will find a number of rings or marks. The age of the fish can be 

 determined by counting these rings. But inside the heads of 

 many fish is a little bone of a flattened or oval shape, called the 

 ear bone or the otolith. It is not strictly the ear bone, but a 

 little nodule inside the hearing organ, helping in some myster- 

 ious way to enable the fish to appreciate vibrations in the 

 surrounding waters. These bones have first an inner white 

 disc, then a dark ring, and next a light ring, and so on white 

 and dark rings alternately. A large number of 6-inch fish was 

 caught, and in the otolith of nearly all of these there were two 

 light and two dark rings. The light rings correspond to the 

 summer growth, and the dark rings to the winter growth. 

 Plaice grew about two inches each year, and one 17 inches 

 long, proved to be seven years and seven months old. The 

 females grow faster than the males. At eight years the female 

 is over eighteen inches, whilst the male is less than fifteen inches. 

 This is probably due to the fact that the males spawn a year 

 earlier than the female, and so stunt their growth. The ordinary 

 sizes of plaice are at three years, eight inches, and at five years,, 

 twelve inches. 



In the southern waters the percentage of males which are 

 mature are : at three years, 20 per cent. ; at four years, 60 

 per cent. ; five years, go per cent. ; six and seven years, 100 per 

 cent. There are scarcely any females in the southern grounds 

 mature at four years, and not more than half until they are 

 six years. In the northern seas there is a year's difference 

 in the time of spawning. Here the majority of the males are 

 not mature until they are five or six years old, as against four 

 years in the southern waters. In the females there is no majority 

 of maturity until they are six years old, and then the large 

 majority of them are mature. 



A line drawn off the Continental coast encloses no fish but 

 what are mostly less than eight inches in length. The next 

 zone further out they are generally from eight inches to ten 

 inches ; in the next zone, ten inches to twelve inches ; g.nd in the 

 next, including a part of the Dogger Bank, twelve to fourteen 

 inches. Towards the north the plaice become larger and larger, 

 on the west portion of the Fisherbank and in the Gut and 

 northern part of the Dogger they are sixteen inches to eighteen 

 inches, and still further north eighteen inches in length. As tO' 

 age, inside the first zone — {i.e., along the Danish and Dutch 

 coast) — they are less than three years old ; in the next zone 



Naturalist^ 



