6 Part HI. — Twenty-fifth Annual Report 



be generally beneficial. Since the Board have no steamer available 

 for this investigation, the work has been done as far as possible by 

 the employment of fishing-boats and the hire of a small sailing 

 yacht for periodical observations in Loch Fyne. 



The Hatching and Reakinc^ of Plaice. 



In the Annual Report for last year an account was given of the 

 reconstruction of the hatchery at Bay of Nigg, Aberdeen, with 

 illustrations showing the exterior and interior, the ponds, pumping 

 plant, &c. The adult plaice from which the spawn is obtained are 

 confined in a large tidal pond, where they are kept and fed throughout 

 the year. At the spawning season the eggs are shed into the water 

 of the pond, from which they are collected by means of a large 

 gauze net, and transferred to the hatching apparatus. They are 

 maintained in the hatching apparatus until the young fishes hatch 

 out, the length of this period depending directly upon the 

 temperature of the water. At tlie commencement of the spawning 

 season, when the temperature of the water is low, the duration of 

 the period of incubation is on the average about three weeks ; at 

 the end of the season, when the temperature has risen considerably, 

 it occupies about a fortnight. The larval fishes, after they are 

 hatched, are kept in the apparatus for several days until the yolk- 

 sac is partly absorbed, and they are then placed in the sea. 



The success of the hatching operations depends very largely 

 upon an adequate supply of eggs and of pure water throughout the 

 season. In order to obtain a large supply of eggs it is necessary 

 that the number of adult fishes in the pond should be large. 

 Hitherto this has been accomplished tolerably well by the employ- 

 ment of a commercial steam- trawler within the territorial waters, 

 particularly in Aberdeen Bay and the Moray Firth, which was 

 used in connection with the investigations of the grounds above 

 referred to. By an arrangement with the owners, the hatchery 

 attendant accompanied the vessel on such occasions, selecting from 

 the catches such fishes as suited the purpose, and these were kept 

 alive in tubs on board and brought to the hatchery. The plaice 

 required were thus obtained gratis, the remainder of the fish 

 becoming the property of the owners. By the method described 

 the stock of spawners has been maintained from year to year ; for, 

 though a large proportion of the fishes of one season survive to the 

 next, there is always a considerable loss which requires to be made 

 good. But, as mentioned in last year's Report, the vessel which 

 was engaged in this work at the end of 1905 was stranded in 

 Aberdeen Bay, and owing to the loss of life occasioned thereby the 

 Board have thought it right to refrain from making use of such 

 vessels in inshore work. In consequence of this, the stock has not 

 been renewed, and the supply of spawn was much less than in 

 former years. Under present circumstances it is not possible 

 to procure supplies of living plaice by means of the ordinary 

 commercial trawlers working in the North Sea. The fish desired 

 are only found in abundance on the inshore grounds, and the cost 

 of obtaining a sufficient number from the offshore would be con- 

 siderable. 



