SEA-FISHERIES LABORATORY, 135 



a large number had been put into a division of the pond, 

 where they developed until the close of the spawning 

 season of the following year. During the winter of 1906 

 the whole pond had been emptied, cleaned out, and the 

 bottom was allowed to dry. It is, therefore, impossible 

 that any small plaice were there at the beginning of the 

 hatching season of 1906, and we may be confident that the 

 fish measured in May, 1907, were just over one year old. 



The sizes of the 200 plaice examined are tabulated 

 on p. 183. They were measured to the nearest ^ inch, 

 and the figures are grouped into J inch classes. The 

 mode is at 2*625 inches, a result which agrees well with 

 what we know of the life-history of the plaice in the sea, 

 and the limits of variation are also concordant with such 

 impressions as I have received on looking over the 

 contents of the catches made by shrimp trawls worked 

 on shrimping areas when small plaice are abundant. It 

 will be seen from the table on p. 163, representing the 

 results of shrimp-net hauls in the Mersey, that the 

 highest percentage of small plaice caught is that about 

 6*5 centimetres (approximately 2' 6 inches). I do not 

 know what these small plaice fed upon in the spawning 

 pond, but the latter was said to contain a very abundant 

 copepod fauna, and on the Mersey grounds copepods form 

 the diet of small plaice up to about 1 inch in length. 



It is evident from a glance at the series of measure- 

 ments on p. 183 that the sizes of these 200 young plaice 

 cannot be arranged in a simple frequency curve. At 

 about 4 inches the numbers of fish in each class begin to 

 increase. It is true that this increase is small, and the 

 total instances are not enough to enable one to be sure 

 as to its meaning. It is, however, quite possible that we 

 are really dealing with heterogeneous data. The spawning 

 pond was stocked with plaice collected (1) from Port Erin 



