LIFE-HISTOKY OF THE PLAICE 37 



the larvae first require a supplementary diet of diatomic plants, 

 not in the period preceding the end of the metamorphosis, 

 but before the absorption of the yolk-sac. It is almost certain 

 that with plaice, as with other small fish, the heaviest mortahty 

 occurs when the yolk has all been consumed, and the fish is 

 for the first time wholly dependent on the food it can find for 

 itself. If the larvae have been unable to obtain floating food 

 to eke out the contents of the yolk from about the fourth day of 

 their fives, they are hkely to be too weak to survive the critical 

 period when they must learn to forage successfully or die. 



The Early Migrations 



On its first ' journey ' the plaice turns from a surface fish to 

 a bottom fish. According to Meek^ it may, if it finds water 

 deficient in salinity, take to the bottom even in the egg stage, 

 or at any stage up to the time it becomes a flat fish. 



Another movement in babyhood is inshore from the spawning- 

 grounds to the ' nurseries '. Not very much is, as yet, known 

 about the stages on this journey. Clearly the eggs and larval 

 fish merely follow the currents. But once a plaice begins to 

 ' swim ' it is possible that instinct teaches it to swim tow^ards 

 the nurseries. At any rate the normal surface drift is towards 

 one or other of these nurseries, and it is there that we next find 

 the fry — on the bottom. 



The Nurseries 

 Plaice fry are found (about two-fifths of an inch long) 

 gradually moving inshore to the nurseries towards the end of 

 April. Their goal is ' the region between tide marks ' (Meek) ; 

 and nurseries are found in the North Sea all down the east 

 coast of Great Britain in depths down to 10 fathoms, where 

 shallow water and fine sandy bottom are found. The largest 

 accumulations naturally occur in areas where these shallows 

 are comparatively broad, i. e. roughly within fines drawn from 

 Flamborough Head to Cromer across the Wash, and from 

 Lowestoft to the North Foreland across the Thames Estuary. 

 Still greater congregations are found off the Belgian and Dutch 

 grounds, but, owing to the set of the drift southwards down our 

 coast as far as the north coast of Norfolk, and (still more) from 

 Dover Straits northv^^ards over the main spaw^ning grounds and 

 along the Dutch coast, more young plaice find themselves on the 

 shallows off the coasts of Denmark, Sleswig, and Holstein from the 

 Horn Beefs into the Hefigoland Bight than in any other region. 

 Here are collected plaice from every portion of the North Sea. 



^ Migrations of Fish, p. 2G4. 



