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PART II. 



The Life-History of the Plaice. 



We next consider the available knowledge as to the life- 

 history of the plaice on the eastern shores of the Irish Sea. 

 There is, of course, much that has still to be investigated with 

 respect to this : the embryology, the possible existence of 

 local races, and the possible spawning-grounds in St. George's 

 Channel and the Welsh Bays. The information that is at our 

 disposal, however, enables us to make such a general picture 

 of the life-history as may be of use to the administrators. 



The Spawning. 



Plaice eggs are found in the plankton collected almost 

 everywhere offshore, between the Solway and Cardigan Bay, 

 in the months of February, March, and April. Exceptionally 

 the eggs have been found in January as the result, we think, 

 of the spawning of fish well to the southward in St. George's 

 Channel. Spawning occurs in the pond at the Port Erin 

 Hatchery during the months of March ^ April, and exceptionally 

 in May. The fish kept in the tanks at Piel, Barrow-in-Furness, 

 spawn a little later, usually about the end of March, in April, 

 and in May. April is the best month for the fish in the tanks, 

 but in the open sea March is perhaps the best month. There 

 is, of course, much variation, from year to year, in the time 

 of spawning, and this is to be associated mainly with the 

 temperature of the sea at the time of spawning and during the 

 previous months, when the reproductive organs are most 

 rapidly developing. It also depends on feeding, as is shown 

 by our experience in the hatcheries, where the fish must be well 

 fed if the roes are to develop fully. A close study of the 

 variations in the temperature of the water (both in the tanks 

 and in the sea) and in the abundance of the eggs found would 



