of the Fishery Board for Scotland. 



lix 



hatch. The period of " incubation " varies with the temperature, and 

 therefore with the season, taking at the beginning of the spawning 

 season in January about three weeks, and about a week less towards 

 its close in May. The larval fishes are retained in the apparatus 

 until the little yolk-sac, with which each is provided, is nearly 

 absorbed, and they are then transferred to the sea at suitable localities 

 and under suitable conditions. 



At the beginning of the season in 1910, about 650 adult plaice were 

 present in the spawning pond. Some of them were, however, as 

 experience showed, rather too small to be reproductive. The spawn- 

 ing was, moreover, somewhat delayed compared with previous years, 

 apparently owing to the severe cold that prevailed. A few eggs were 

 collected from the spawning pond on 9th February, and thereafter 

 the number gradually increased until the latter part of March and 

 the beginning of April, after which the eggs began to get scarcer, the 

 last being obtained on 18th May. 



The number of eggs collected in each month, and the percentage, 

 were as follows : — 



No. of Eggs Collected. Percentage. 

 February, - - 707,000 - 9-0 

 March, - - - 4,523,000 - 57-4 

 April, - - - 2,505,000 - 31-8 

 May, - - - 145,000 - 1-8 



7,880,000 



The total of 7,880,000 was much less than in 1909, when 19,749,000 

 eggs were obtained, the decrease being 11,869,000. An examination 

 of the fish in the pond showed that many of them were too small in 

 size, and were in fact immature. 



The estimated number of fry obtained during the season was 

 6,880,000, or about 87 per cent, of the aggregate number of eggs, the 

 loss thus being about 13 per cent. This relatively favourable result 

 was in large measure owing to improvements in the methods of 

 filtering the sea water, the presence of fine mud being one of the chief 

 causes of the mortality among the eggs while they are kept in the 

 incubating apparatus. The fry were placed in the sea in nine lots, 

 between the 23rd March and the 26th May, about 6,000,000 being 

 taken to Fraserburgh, Peterhead, St. Combs, and Cruden Bay, and 

 liberated at some distance from shore in these localities ; the remainder 

 were liberated in Aberdeen Bay. 



Since the hatching of the plaice was begun at the Bay of Nigg a 

 total of 378,801,000 eggs of the plaice have been dealt with at the 

 Hatchery, and 293,164,000 fry have been liberated in the sea. During 

 the first two years most of the fry were transported to Lochfyne, in 

 continuation of an experiment which had been begun many years 

 previously with the object of ascertaining the efiect of the liberation 

 of the fry on the abundance of the older stages of the fish. This 

 experiment is fully described in the Twenty-sixth Annual Keport. 

 The output at the Hatchery since 1900 is given in the subjoined 

 Table :-- 



