338 Part IIl—Tirentieth Annual Report 



the approximate average size at that period differed in different seas.* 

 Ten inches was assigned as the average size at maturity in the Baltic. 

 Petersen had earlier published another paper in which he briefly dealt 

 with the subject, and which is of interest inasmuch as in this paper he 

 first made use of the method employed in the present investigation, 

 by the assortment of the fish into groups. t 



In 1898 Mr. H. Dannevig made an investigation at Dunbar on 

 the rate of growth of this species, the fish being obtained at three 

 localities, or depths, up to five fathoms. The number of specimens of 

 the first, and occasionally of the second series, was considerable, and 

 the conclusion reached was that the average growth of the plaice during 

 the first year was about 77 mm., during the second year 79 mm., and 

 during the third year about 76'4 mm. He concluded that the average 

 growth is a little greater in the second than in the third year ; that 

 the average length of plaice was 77*2 mm. when one year old, 156'7 mm. 

 when two, and 233 mm. when three years old, and that the plaice was 

 ordinarily not mature till its fourth year J 



The investigations referi-ed to were made on collections in which the 

 .sexes were not separately distinguished, but this circumstance does not 

 materially affect the results until the fish are about three years of age, 

 since the males and females in this species grow with almost equal 

 rapidity during adolescence. After that period, however, it is 

 necessary to distinguish the sexes, since the males grow much more 

 slowly than the females. 



I shall now endeavour to trace the growth of the plaice as 

 indicated by the observations made by myself. The investigations were 

 for the most part carried on on board trawlei'S fishing in Abeixleen Bay 

 and the Moray Firth, a small-meshed net being placed around the 

 cod-end of the otter trawl, as previously described, and considerable 

 numbers of fish were sometimes measured. These observations 

 were supplemented by others with a shrimp trawl in the Solway 

 Firth used in shallow water from a few feet at high tide to five 

 fathoms, while collections of the very smallest plaice were made by 

 means of a push-net on the beaches. The collections of these small 

 fish were considerable and consecutive, and it will be desirable to 

 begin with them first, and to trace the growth of the plaice during its 

 first year, from the time the eggs are spawned. 



On the East Coast of Scotland the spawning period extends, as a 

 rule, from the end of January until the beginning of May, the 

 maximum, according to the propoi-tion of spawning fishes, being in 

 March. This agrees with the limits of the spawning of the plaice in 

 confinement in the ponds at Dunbar and the Bay of Nigg, the first 

 fertilised eggs being collected from the water towards tlie middle or 

 end of Janviary or the beginning of February, most being obtained in 

 March and the last in the beginning of May. But variation may take 

 place to some extent, influenced apparently chiefly by changes in 

 temperature. The floating eggs of the plaice, moreover (which are 

 easily identified), were obtained in the Firth of Forth and neighbour- 

 hood from early in February until the end of May — in one year one 

 was got in the tow-net on 4th June — and they were found in Loch 

 Fyne from the end of February until the beginning of June, most 

 being obtained in April and towards the end of March. § 



* Report of the Danish Biological Station to the Home Department, iv., pp. 6, 22, 33 

 (1893). 



+ Beretning til Indenrigsviinisferielfra den d^insh Biologtsl:e Station. Copenhagen, 1892. 



X Seventeenth Ann. Rep. Fishery Board for "Scot/and, Part iii., p. 232 (1898). 



§ Masterman, Fifteenth Ann. Rep. Fisher,/ Board for Scotland, Part iii., p. 229 (1897); 

 Williainson, -iln'd., Seventeenth, iii., 97 (1899). 



