o/ the Fisheri/ Board for Scotland. 7 



the common dab, practically all that are marketable are mature, 

 this fish becoming reproductive at a small size. Among plaice, on 

 the other hand, which does not attain maturity until it is several 

 years of age and of some size, the proportion of the immature 

 amounts to about twenty-four per cent, of the marketable fishes, 

 but with this species in particular the proportion varies much 

 according to the chief areas of fishing. Among the witch sole the 

 proportion amounts to about fifteen per cent., and it is still less 

 among lemon soles, viz., about seven per cent. From the large 

 size at which the cod first reaches maturity, the proportion of the 

 immature that are marketable is considerable ; these comprise 

 codlings, and of the total quantity landed about thirty per cent, are 

 sexually immature. AYith haddocks, and still more with whitings, 

 the proportion is much less, these species first attaining maturity 

 at about the size at which they become marketable. The calcula- 

 tion in regard to haddocks shows that the proportion of the 

 marketable which are immature is small, amounting to only about 

 one per cent, of the quantity landed, while among whitings it is 

 less, practically all the whitings caught by trawlers which are of 

 marketable size being adult. 



It must be borne in mind, with reference to this subject, that 

 the limit between the mature and the immature is a biological one, 

 having reference, not to the size of the fish from the market point 

 of view, but in relation to the size when reproduction begins. 



Investigations on the Eate of Growth of Fishes. 



In the present Eeport will be found a paper by Dr. T. Wemyss 

 Fulton describing the results of his further investigations on this 

 subject, in continuation of the researches detailed in some of the 

 preceding Eeports. In addition to the measurement of large 

 numbers of fishes obtained during the trawling investigations by 

 the use of a small-meshed net, numerous observations were made 

 to determine the relation between the size and weight of fishes 

 belonging to nineteen species, and a series of experiments were 

 carried on to show the influence of temperature upon growth. 



With regard to the ratio between the length and weight of fishes, 

 it might be assumed, without experimental evidence, that their 

 growth was in consonance with the physical law governing the 

 relation of similarly-shaped bodies of uniform specific gravity with 

 regard to weight and dimensions — that the weight increased as the 

 cube of the length, so that a fish which doubled its length should 

 increase its weight eight times. The observations, which have been 

 made on between 5000 and 6000 fishes, show that this law does not 

 apply with exactitude in any of the species examined, the weight 

 increasing in proportion more rapidly than the length, the conclu- 

 sion being that, if the specific gravity remains the same, growth 

 takes place to a greater extent in some other dimension than in 

 length, whether in breadth or thickness. The various species 

 examined displayed great differences in the relation between the 

 weight and length at a given size, the heaviest in proportion to its 

 length being the turbot, and the lightest the witch, the extremes 

 being found among the flat-fishes. 



