of the Fishery Board for Scotland. 



281 



X. -ON THE SPAWNING AND FECUNDITY OF THE PLAICE 

 (PLEURONECTES PL A TESSA ). By T. Wemyss Fulton, 

 M.D., F.R.S.E., Superintendent of Scientific Investigations. 



The spawning period of the plaice has been very well determined for 

 various parts of the North Sea. On the east coast of Scotland it extends 

 from the end of December in some years, but more usually from the early 

 part or middle of January, to the early part or middle of May, the chief 

 spawning taking place in March. 



The records of the Marine Hatchery at Aberdeen furnish some details 

 of interest as to the length of the spawning season and the intensity of 

 spawning in the various months. Thus last year eggs were obtained from 

 the spawning pond for 117 days, from 20th January till 16th May. The 

 number of eggs obtained in the various months during the last three 

 years, and the percentages of the total, are as follows : — 



Jan. Feb. Mar. Apr. May 



Fig. 1. 



The curve (Fig. 1) formed by these figures is very regular, and, as will 

 be seen, the spawning is at its height about the middle of March. 



It has not yet been shown, however, over what part of the period a single 

 female continues to discharge her eggs. It is well known that most or all 

 fishes producing isolated pelagic eggs do not get rid of them at once. 

 They are spawned in relatively small quantities at a time and over a 

 longer or shorter period. As I have elsewhere shown,* this is a physical 

 necessity, since a female cannot hold all the eggs at the size they possess 

 when mature, and they must ripen gradually and in succession. 



It was in order to determine the duration of the spawning in a single 

 female, and some other points in connection with spawning, that the 

 following experiments were chiefly made. But another object I had in 

 view was to ascertain the number of eggs actually shed into the water, 

 i.e., the real fecundity. This has been approximately determined for the 



* "The Comparative Fecundity of Sea Fishes," Ninth Annual Report, Part III., 

 p. 242: "On the Growth and Maturation of the Ovarian Eggs of Teleostean Fishes.'' 

 Sixteenth, Ibid., p. 88. 



