150 



Part III — Twenty-second Annual Hepor 



From this it will be seen how very greatly the weight and therefore the 

 amount of growth in different members of the same series may vary. 

 The " range of the mean," moreover, refers to the average weight for the 

 longest and shortest fish in a series ; the actual or possible variation in 

 weight is much greater, as may be seen from the Tables for the plaice on 

 p. 205. 



3. The Average Size at Maturity. 



With regard to the size and age at which the males and females of the 

 various species of food-fishes first attain maturity, a great deal of infor- 

 mation is still required. Isolated observations have been made in a 

 considerable number of instances on several species, sufficient to give an 

 approximate idea of the limit between the mature and the immature, but, 

 as a rule, they are not of such a kind as to enable the average-size as 

 well as the extremes to be determined, and on the hypothesis that 

 reproduction takes place at a certain age this average-size should 

 correspond to the average for one or other of the yearly groups. 



In one or two cases I have made a number of observations on the 

 subject, particularly with regard to the plaice, the haddock, and the 

 whiting, a number of these fishes being examined at the spawning time, 

 the sexes determined, the condition of the reproductive organs noted, and 

 the size of the fish measured. 



A number were also examined at periods anterior to the spawning time 

 and the progress of the development of the eggs observed. 



Thus, among twenty-four whitings caught in the Moray Firth on the 

 14th November, comprising sixteen females and eight males, it was found 

 that the former ranged in size from 242 to 418mm., and in weight from 

 108 to 517 grammes; the weight of the ovary varying from 0*2 to 38 

 grammes, and the diameter of the eggs from "189 to '294mm. The 

 following are selected examples : — 



Length. 



Weight. 



Weight of 

 Ovaries. 



Diameter of 

 Largest Eggs. 



Mm. 



Gr. 



Gr. 



Mm. 



242 



108 



0-4 



•189 



248 



110 



10 



•231 



293 



196 



1-7 



'294 



298 



198 



1-5 



•252 



304 



223 



2-1 



•231 



313 



240 



1-8 



•189 



351 



354 



2-8 



•273 



418 



517 



38-0 



'273 



The particulars in these examples show that the whitings, and probably 

 even the smallest, would spawn at the next spawning season \ and it will 

 be observed that the size of the eggs in some of the smaller specimens is 

 as large as in those of considerably greater size. In the males the weight 

 of the testes was also determined, and their weight did not always 

 correspond with the weight of the fish, as the following examples 

 indicate : — 



