of the Fishenj Board for Scotland. 361 



luaximum being probably attained iu the early part of May.* At 

 this time the temperature of the sea is rising steadily (see p. ), and 

 the eggs, which are much smaller than those of the plaice, hatch in 

 May in eight oi' nine days. The larval fish is also relatively small, and 

 measures about 2*6 millimetres ; it is thus only about a third of the 

 size of the early hatched plaice. 



We have not the same information as to the time taken by the dab 

 to go through its metamorphosis, as we have concerning the plaice, but 

 according to Petersen's observations the post-larval dab remains pelagic 

 until it attains a larger size than the post-larval plaice — i.e., it is largei' 

 when it begins life on the bottom. He states that while in Danish 

 waters the pelagic stage of the plaice ends when the fish is 10 to 11 nun., 

 it does not seem to end in the common dab until a length of from 

 twelve to thirteen millimetres is reached.t Professor M'lntosh also 

 points out certain features which support this statement of Petersen's, 

 and he thinks that the dab, although a smaller fish than the plaice, 

 takes a longer time, oi- at least attains a greater size, before completing 

 its metamorphosis. t 



Holt figures a specimen 1225 mm. long which is nearly at the same 

 stage as a young plaice of 10 mm., and in which the left eye is not yet 

 over the edge. He figures another 15*25 mm. long in which the 

 transformation has been almost completed. § Dr. Kyle, in the paper 

 previously alluded to (p. 358), states that the limits of complete transfor- 

 mation are probably between 16 and 18 mm. 



The facts above stated suggest that the duration of the pelagic stage 

 of the dab is longer than in the plaice, since in the interval between 

 its issue from the egg and its settlement on the bottom after trans- 

 formation, it gi'ows about 13 or 14 mm. in length, or more than 

 double the corresponding increment added by the plaice. At the same 

 time it must be borne in mind that the temperature of the water is 

 much higher during the period of the pelagic life of the dab, and thus 

 growth and metamorphosis will be more rapid. Post-larval dabs have 

 been procured in the tow-nets in April, May, June, July, and August, || 

 mostly at the end of May and first part of June. As many as 3000 wei'e 

 caught in surface tow-nets on 16th and 19 th May fifteen miles off the 

 coast between Montrose and Aberdeen. It is probable that the 

 great bulk of dabs begin their life on the bottom about the middle or 

 end of June. 



For comparison with the plaice I here append temperatures for ten- 

 day periods from the beginning of February to the end of June, derived 

 from the mean of surface and bottom temperatures at five stations 

 near and beyond the mouth of the Firth of Forth in depths varying 

 from eleven to thirty-two fathoms, viz. : — 



41-5, 41, 40-8, 40-5, 40, 40-9, 41-7, 42-5, 43-5, 44-6 | 45-8, 46-8, 477, 48-9, 49-7. 



The earliest collections of small dabs obtained by me betv^een one 

 spawning season and the next were as follows : — 



* Tenth Ann. Rep. Fisher)/ Board/or Scot., iii., '234. 



t Op. cit., p. 126. 



:J: British Marine Food Fishes, p. 378. 



§ Sci. Trans. Roy. Dub. Soc., v. (Sec. vi.), pi. xiv. 



II Kyle, op. cit. 



