8 



Part III. — Twenty-fourth Annual Report 



now somewhat enlarged ; a concrete floor replaces the old wooden 

 one ; a strong wall has been built along the seaward face of the 

 site, and granite retaining walls around the gravitation tank. In 

 the present Eeport a brief description is given of the hatchery as 

 rearranged, with illustrations showing the interior and exterior, the 

 pumping plant, and the large spawning-pond in which the breeding 

 fishes are kept and where the eggs are shed at the spawning 

 season. 



During last year the eggs of the plaice were first discovered in 

 the pond on 20th January, about the usual date when they make 

 their appearance. Collections of eggs were thereafter obtained 

 almost daily. The numbers gradually increased until the middle 

 of March, after which they declined until 16th May, when the last 

 collection was made. The duration of the spawning in the pond 

 was thus about 117 days, which may be regarded as approximately 

 the period in the sea. The aggregate number of eggs collected in 

 the season was estimated at 40,110,000, of which 48 per cent, were 

 spawned in March, 23 per cent, in February, and the same pro- 

 portion in April. 



The duration of the period of embryonic development, until the 

 eggs hatch, varies with the temperature of the water. The average 

 at the beginning of the season, when the temperature is low, is 

 about three weeks ; towards the end of the season, with the 

 temperature some degrees higher, hatching takes place in about a 

 fortnight. The larval fishes, on issuing from the eggs, are retained 

 in the apparatus for several days until the yolk-sac is partly 

 absorbed, and it is calculated that the eggs and larvae are protected 

 in this way for about half of the time from the spawning of the 

 eggs until the young plaice undergo their metamorphosis and 

 assume the form and habit of the adult. 



The estimated number of fry which hatched out and were placed 

 in the sea was 24,500,000. Most of them were distributed off 

 Aberdeen, but one lot of about three and a half millions was taken to 

 St. Combs, further up the coast, at the request of the fishermen, 

 and there distributed. 



Since the establishment of the hatchery the total number of the 

 fry of plaice which have been set free in the sea amounts to 

 387,750,000, the number of fry of other fishes, as turbot, lemon 

 dabs, and cod, being close upon 17,000,000. 



Owing to the circumstance that the hatchery is worked in con- 

 junction with the Marine Laboratory, the expense of the hatching 

 operations is comparatively small, the annual expenditure being 

 estimated at rather under than over £100, which meets the cost of 

 extra coal and an additional assistant at the height of the season. 



Scientific and Technical Instruction to Fishermen. 



For some years past, as mentioned in previous Eeports, by an 

 arrangement with the Technical Education Committee of the 

 County Council of Aberdeenshire, representative fishermen from 

 various parts of the coast of that county have visited the laboratory 

 and hatchery in spring, to attend demonstrations on the life- 



