360 Part III. — Twentieth Annual Report 



diiFerences in the rate of growth exist in different localities I have shown 

 also to hold in the case of the long rough dab (p. 385); and it is, I 

 believe, the cause of the variations in the size at first-maturity, which 

 Cunningham found among plaice collected from ""^arious localities, 

 sometimes not far apart, in the southern part of the North Sea. It is 

 a subject worthy of further investigation. 



With regard to tlie males, it is indeed possible, as some observations 

 appear to indicate, that maturity may be in exceptional cases reached 

 at an earlier age than normal ; but all the facts in connection with 

 the role of the males among fishes tend to show that its part in 

 reproduction is less fundamentally associated with the organism than 

 in the case of the female, and is subject to greater variability. Ripe 

 males, for example, may be found long before and long after the spawn- 

 ing season. With the female everything is subordinated to the produc 

 tion of eggs, and since growth shows such marked seasonal rhythm and 

 periodicity that reminds one of the phenomena of terrestrial 

 vegetation, I think it must rarely happen that spawning occurs before 

 the attainment of a definite age. 



According to these investigations the males become mature when 

 four years old, and the females when five years old. 



THE COMMON DAB {Pleuronectes limanda, L.). 



The rate of growth of this flat-fish appears to have been but little 

 investigated. Mr. J. T. Cunningham, from the comparison of a 

 number of specimens (over three hundred), froia 14th June 1890 to 

 18th September 1891, came to the conclusion that while five and a 

 half inches was about the maximum length reached by a dab in one 

 year, and small specimens measuring 1*8 inches in May represented the 

 minimum, the great majority at one year old were below the size first 

 mentioned. He estimated the approximate size of the dab at different 

 ages as folloAvs : — First year, 2 to 6 inches; second year, 5 to 8 inches; 

 third year, 7 to 10 inches; and he was of opinion that the dab did not 

 breed before it was two years old.* Dr. Petersen also showed the 

 existence of different groups in Danish waters, but without apparently 

 stating his opinion as to their age. 



Mr. H. Ch. Williamson, by the comparison of a number of specimens 

 (49) caught at different times and dates, came to the conclusion that 

 four caught in January, ranging in size from 14 to 17*5 mm. were probably 

 from seven to ten months old; others caught in March, from 20 to 52 mm., 

 were at least nine months old, the larger perhaps older ; that six 

 specimens from 70*5 to 106 mm., caught in Septeniber, were sixteen to 

 seventeen months old ; and two specimens 146 and 148 mm., taken at 

 the end of April, were two years old.t 



The investigations made by me as to the growth of this fisla were 

 carried on as with the plaice, partly on board trawlers, and partly with 

 a shrimp-net and push-net in shallow water. Since the dab is one of 

 the commonest flat-fish in the areas examined, a considerable number 

 were measured and the sexes in most cases distinguished. The smallest 

 series were first secured in July, but before dealing with them it will be 

 well to consider the spawning season. 



The spawning season of the common dab is later than that of the 

 plaice, and extends on the East Coast from late in February to June, 

 or even into July, but it occurs mostly in April, May, and June, the 



* Journ. Mar. Biol. A.isoe., ii., 101. 



t Eleventh Ann. Rep. Fisher<j Board for Scot., Hi., p. 267. 



