156 R. J. H. Beverton and S. J. Holt 



protracted than in most higher vertebrates, and as a conse- 

 quence the maximum size is often not reached within the 

 range of age covered by the data. This makes it necessary 

 to examine in more detail the actual pattern of growth in 

 fish in order to arrive at suitable indices to correlate with 

 longevity. 



Fig. 2 gives a few examples of the growth in length of fish. 

 We use length as the measure of body size rather than weight 

 because, as can be seen from Fig. 2, growth in length nearly 

 always follows a simple curve without an inflection.* This 

 is true whether the species is one which can grow to a large 

 or to a small size, and whether it completes its growth 

 pattern rapidly or slowly. Examples of all these are included 

 in Fig. 2. 



In the upper part of the diagram is shown the growth of 

 sturgeon {A. nudiventris), which both grows slowly (i.e. com- 

 pletes its growth pattern slowly) and also attains a large size, 

 that of sockeye salmon (0. nerka; Foerster, 1929) which grows 

 to a fairly large size but does so rapidly, and that of whitefish 

 {Coregonus clupeaformis) which grows slowly to a rather smaller 

 size. In the lower part of Fig. 2 are some examples of the smaller 

 species, and for these the scales of both length and age are 

 increased roughly fivefold; to aid comparison, the growth of 

 Lusterfjord herring {Clupea harengus; Aasen, 1952) is shown 

 in both parts of the diagram. It will be seen that although 

 the smaller species usually develop their growth pattern more 

 rapidly than do the larger species, there is still quite a range 

 of variation. Thus, for its size, the blenny {Blennius pholis; 

 Qasim, 1957) is relatively slow-growing, whereas Labidesthes 

 has virtually reached its maximum size in little more than a 

 year; and the 10-spined stickleback (Pygosteus pungitius; 

 Jones and Hynes, 1950), although growing to little more than 

 half the size of Labidesthes, takes several years to do so. 



* Since the growth of most fish is closely isometric after the juvenile phase, 

 the curve of growth in weight is approximated to by cubing that of growth in 

 length. This produces a weight-growth curve which has an inflection at about 

 one-third of the asymptotic weight. 



