of the Fishery Board for Scotland, 



263 



earlier than usual, was natural. The ordinary duration of the spawning 

 season of the plaice appears to be about the longer periods, extending 

 over three full months and part of other two — and the observation is of 

 some importance in fishery investigations. 



Eggs were observed in small numbers a few days before the regular 

 collection began, and a few were found after the date when the collection 

 ceased. The total number of eggs secured from the pond by means of 

 tow-nets was about 65,940,000, the eggs being measured in a vessel of 

 known capacity and the number thus estimated. Spawning took place 

 for the most part in March, the numbers of eggs secured in the various 

 months being as follows : — 



January, - - - 240,000 



February, - - - 11,840,000 



March, - 37,080,000 



April, - 15,900,000 



May, - - - 880,000 



In some years the bulk of the spawning occurs in the early part of 

 April. On some mornings in March last year as much as five gallons 

 of eggs were taken from the pond. Of the number of eggs collected 

 81 per cent, were hatched, and the remainder succumbed at one stage 

 or another in the apparatus ; there is reason to suspect that some of 

 the eggs which are lost in this way are not fertilised, a tendency having 

 been shown to economise the space in the pond by having in it an 

 unduly large proportion of females at the expense of the number of 

 males. 



The estimated number of fry which were hatched and kept for a 

 period in the apparatus was 53,600,000, and they were afterwards 

 placed in the sea, most of them being liberated a few miles off Aberdeen, 

 by means of a fishing yawl. At the request of the line-fishermen 

 further up the coast a number were set free on three occasions ofl 

 Fraserburgh, the total distributed there being about 16,000,000. 



The particulars as to the distribution of the fry and the details as to 

 the numbers of eggs collected throughout the season are given in the 

 tables appended, which also show the variations in the temperature and 

 the specific gravity of the water in the spawning pond and on the 

 beach. 



The number of fishes kept in the pond to act as the breeding stock 

 was as usual supplemented in autumn by others caught by means of 

 trawlers and brought alive to the hatchery in large tubs ; for there is 

 always a certain amount of natural mortality among them, particularly 

 during the summer. The plaice, as hitherto, were fed on mussels, which 

 are usually removed from their shells, but are sometimes only crushed. 



The ponds and apparatus, which have been described in preceding- 

 annual reports, continue to serve their purpose well, and the water 

 supply, both in regard to temperature, density, and purity, is very 

 suitable for the work. The only changes that have been made in the 

 arrangements consist in the removal of the water tumbling-box from 

 the inside of the hatchery, where it was served with the incoming water, 

 to the outside, where it is now operated by the out-flowing water. The 

 box is necessary to provide the motive power to the Dannevig hatching 

 apparatus, and it was found to interfere to some extent with the 

 pressure of the water to one side of the hatchery and thus to retard the 

 supply. Also by the fitting up of the tank-house for scientific experiments 

 it was found necessary to divert a portion of the water from the 

 reservoir tank for this purpose, and the change necessitated a little more 

 pumping early in the mornings. 



