of the Fishery Board for Scotland. 



289 



X. — ON THE RATE OF GROWTH OF THE MARINE FOOD 

 AND OTHER FISHES. I. The Rate op Growth of the Plaice. 

 By Arthur T, Masterman, B.A., Assistant Professor of Natural 

 History in the University of St Andrews. (Plate XIV.) 



The rate of growth of Teleostean fishes seems to be one of a class of 

 subjects upon which reliable statistics are very hard to obtain, and it is 

 remarkable what divergent opinions are held in regard to it. In deal- 

 ing with the same, it would be well to first consider the various factors 

 which enter into, and which may be considered the direct causes of, 

 diversity in the rate of growth of various members of a species of Teleos- 

 tean fish, such as, for instance, the plaice. 



Limit of Growth. — The problem of the growth of fishes is very 

 different in many ways from that of the growth of am n iota. As one 

 would expect, from theoretical considerations, the fish as an organism 

 shows itself to be more directly susceptible to the influence of its environ- 

 ment. Thus, as mentioned below, the period of incubation can be 

 altered at will between very wide limits by simply varying the tempera- 

 ture, whereas one would hardly expect to alter the period of mammalian 

 gestation, or even of avian incubation, except within extremely narrow 

 limits. Other instances could easily be given to show that the direct 

 effect of the environment upon the piscine organism is much greater than 

 that upon land organisms. Without considering the effect of environ- 

 ment, it is probable- that the life-cycle of the individual fish also differs 

 in very important respects from that of the higher animals. 



In the mammalia there is a definite duration of growth in bulk and of 

 life quite apart from the environment, and either period can only be 

 altered by continued action of the environmental factors through many 

 generations. There are some experiments which point to the conclusion 

 that the duration of life of the individual fish is only limited in the 

 widest sense (with immunity from environment), but leaving this out of 

 the question there is no proof forthcoming of the hypothesis that the 

 individual fish ceases to grow at any period of its life ; on the contrary 

 there are considerations which point to the other view, i.e., that a fish 

 continues to grow throughout its life. 



Thus, if a mammalian or avian species be subjected to the destroying 

 agency of man, there follows a diminution in numbers ; whereas, if a fish be 

 subjected to like conditions a reduction in the size of the individuals is 

 the immediate result. These facts can be explained as follows : — In the 

 former case very little, if any, growth in size takes place after the attain- 

 ment of sexual maturity, whereas, in the latter case, growth continues 

 indefinitely after that event. The amount of growth per annum may be 

 expressed as a certain proportion of the whole, and must form an ever- 

 decreasing geometrical series, so that the total amount of growth is only 

 limited in the same sense as 1 + \ + \ + -J, etc., is limited in a finite series 

 to less than 2. A study of the average sizes of fish shows that the 

 annual increase is practically distinctly appreciable. There is no reason, 

 therefore, to believe that there is any definite limit to the size of a 

 fish, as used in the sense in which we speak of a definite size attained 

 by mammals and birds, beyond which growth in bulk does not 



