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Part III. — Twenty-first Annual Report 



IV. — REPORT ON THE OPERATIONS AT THE MARINE 

 HATCHERY, BAY OF NIGG, 1902. By Dr. T. Wemyss 

 Fulton, Scientific Superintendent. 



In previous reports the methods and arrangements in connection 

 with the hatching of plaice have been described, the principal conditions 

 of successful working being the providing of a good stock of adult fishes 

 to furnish the spawn, and an abundant supply of pure sea water of 

 proper density for the hatching apparatus. 



Since the erection of the hatchery on its present site in the autnmn 

 of 1899, it has been found possible, by means of the large, sunk, tidal 

 pond, to keep a breeding stock from one season to another instead of 

 renewing it yearly, as was previously the case. Under the former- 

 system it took a considerable time for the fishes to become accustomed 

 to confinement, and many of them did not spawn, but retained their 

 eggs, and died in an egg-bound condition, and thus the quantity of 

 fertilised spawn obtainable from a given number of fishes was materially 

 reduced. 



At the end of the hatching season in 1901 the number of plaice 

 remaining in the pond was found to be 767, most of which continued 

 to thrive during the summer and autumn. To these others were added 

 in the winter, the fishes being procured on board steam-trawlers provided 

 with large covered tubs, through which a constant circulation of water 

 was maintained, and which were transferred to the hatchery and the 

 fishes placed in the pond. At the end of November 21 were obtained 

 from Aberdeen Bay, in December 345 from Burghead Bay in the 

 Moray Firth, and early in January 120 from off* the coast of Caithness. 

 As is always the case, a considerable number of the newly-introduced 

 fishes succumbed later, chiefly in consequence of injuries and abrasions 

 received in the course of capture by the trawl-net, and partly as the 

 result of abrasions in the tubs, where they were sometimes confined for 

 several days. The breeding stock for the season was estimated to 

 number about one thousand plaice of both sexes. 



During the latter part of January the temperature of the water in 

 the pond was rather lower than usual, and few eggs were observed 

 to have been shed until the early part of February. The first collection 

 was made from the spawning-pond on the 8th February, when about 

 20,000 eggs were obtained, and on the next two days alDOut the same 

 quantity. Owing to a hard frost occurring on the following days the 

 temperature of the water sank and spawning was checked, and no 

 further collection was made until the 17th, when 40,000 were obtained. 

 In the first half of March the number of eggs greatly increased, over 

 two millions, and occasionally nearly three millions, being taken from 

 the pond daily, the aggregate up to the 16th March being over 

 38,000,000. After this period the number diminished in March and 

 still more in April, and the last collection was made on the 25th of 

 April, viz. 20,000. 



During the season the large total of 72,410,000 eggs were obtained, 

 or about seven millions more than in the preceding year. It is believed 

 that this large total was mainly owing to the thorough acclimatisation 

 of the majority of the spawners during the year or more in which they 

 were kept in the tank. It may be said that the fishes in the course of 

 time become very tame, instead of withdrawing themselves and skvilking 

 at the bottom of the tank as is the habit with those newly introduced. 

 They frequently swim about the surface at the sides of the tank in 



