36 LIFE-HISTOB\^ OF THE PLAICE 



unconscious wrigglings, must attract very much more notice to 

 themselves than the floating eggs. Fortunately in temperate 

 waters hke the North Sea this period of extreme danger is 

 believed to last for about one week only. 



Post-Larval Period 

 Before the food in the yolk-sac is all consumed, i.e. 

 generally about the fourth day, the larvae begin to feed them- 

 selves ; they must from this time on be more or less capable 

 of steering a course and breasting a current. Their food 

 consists of diatoms, the larvae of molluscs, &c. About the 

 twelfth day the j^olk-sac is completely absorbed and the post- 

 larval stage is completed. It lasts about one week. This 

 period is accepted as the critical period by fish culturists all 

 over the world. It starts with the time when the mouth first 

 begins to function, and ends with the first absorption of the 

 yolk-sac, though the evils produced by infantile troubles may 

 not manifest themselves till the next stage is reached. 



The Fry Stage 



(a) The plaice is now a fish, not a ' flat fish ' but a round 

 fish, poised and swimming like any young cod or mackerel or 

 haddock. At the end of twenty-one days from hatching it is 

 only three-eighths of an inch long. Its food now includes the 

 young of various crustaceans. 



(b) After the thirtieth day the fish take to eating small 

 copepods as well as larval molluscs and crustaceans. The left 

 eye begins to move over the top of the head, and by the forty- 

 fifth day it is on the same side of the head as the right eye. 

 Meanwhile the fish has taken to swimming on what was 

 originally its left side,^ and is now a * flat fish fry '. At this 

 stage it is about three-fifths of an inch long. What naturalists 

 call the ' metamorphosis ' is now complete, i.e. the fry sink to 

 the bottom and take to feeding on small worms, shrimp larvae, 

 and other crustaceans which live on the bottom. It is often 

 said that the whole hfe of the plaice is one of danger up to the 

 end of the metamorphosis. This is no doubt true, but it is 

 clear that the danger is extreme in the larval week and in the 

 three or four weeks during which the eggs float about in the 

 sea. Comparative security is reached (and must increase 

 progressively) as the fish gradually attain volition in their 

 search for food. The climax of risk is probably reached when 



^ Plaice, soles, lemon soles, dabs, flounders, witches, halibuts, and the long 

 rough dab swim on their left sides ; turbot, biill. and megrims on their 

 right sides. The flat fishes swim on that side which is the heavier. 



