to No^ 10 were used:, The method of measuring vtss the same as for the bl;:,ck tuna. 

 (Table 6)c 



In some cases v?hat appear to be annual rings having radii of over 3 7 mm can 

 be observed^ btit it is thought that these result from irregularities in the 

 structure of the central portion. ^1/here the variation of the radius in compari- 

 son vd.th other annual rings is very marked, the line cannot be considered an an- 

 nual ringo Accordingly those of 5.6+0c20 mm \vere taken as the first ring (r^) , 

 The correlation between the total radius of the centinira (T mm) and the length of 

 the fish (L cm) is shown by L^/l^ a (Tj^ - 1)^*2 " ^^« ^'^o™ *^^ radius r^ mm of 

 annual ring No. n, the length (Lq cm) at iriiich the ring nas completed can be 

 found by the following formula: 



Ln s 8.4 r^ - 8.4 



Table 7 shows the range of lengths for each age^ The results of measure- 

 ments taken on small yellowfin landed at Numazu market from June to August 1936 

 show (Table 8) that the condition factor for yellowfin tuna varies between 20 and 

 30, and that it decreases as the fish grows older. Taking this change into con- 

 sideration, the weight range for fish of each age group was estimatedo The 

 weight of fish of the year and second-year fish is thought to be somewhat greater 

 than these calculations indicate. The rate of groivth of the yellowfin is much 

 lower than that of the black tuna, Kimura (op.cit.) attempted to determine the 

 growth rate of yellowfin from morphometric data collected at Omodera, and for 

 fish up to their third year his results are in general agreement with those ob- 

 tained by the author, but for older fish, just as in the case of the black tuna, 

 he is greatly in errorc 



Yellowfin landed at the Numazu market from May to August of 1936 comprised 

 weight groups having their modes at 1.2 kan j]9<.9 IbsJ, 2.4 kan (19.9 IbaJ , 4 kan 

 [33.1 IbSc], 6 kan [49.6 lbs.], 8 kan [^2 lbs.], and 12 kaij [99.2 Ibs.^j, The 

 catch from September to December contained three groups having their modes at 0,5 

 kaa [4,1 lb3,j, 1.2 kan j^,9 lbs.], and 2.0 kan [16,5 lbs3. The 0,5 kan group 

 are clearly fish of the ye«ur and the others belong to age classes from the second 

 to the seventh year, 7feight groups are seen which agree with the weight ranges 

 given for the various year classes in Table 7. In the spring catches the 2 kan 

 and 6 kan groups do not show up very clearly, but their existence is undeniable. 



Table 7 Age, length and weight range, growth rate, and condition 



factor of yellowfin 



Age Length ffeight Growth Rate Cond, Factor 



<3S em <1,50 kg 27.0 



38-54 1,50-4.3 1.05 27,0 



Fiah of the year (0 age group) 



Second-year fish (I age group) 38-54 1,50-4.3 1.05 



Third-year fish (II age group) 54-70 4,3-8.6 0.70 



Fourth-year fish (III age group) 70-85 8.6-I4.O 0.49 



Fifth-year fish (IV age group) 85-100 14.0-21.4 0.43 



Sixth-year fish (V age group) 100-115 21.4-34.0 0.37 



Seventh-year fish (VT age group) 115-130 34.0-44.0 0.30 



Eighth-year fish (VII agft group) 130-145 4400-57. 5 0.27 



Ninth-year fish (VIII age group) 145-160 57.5-75.0 o.24 



25.0 

 23.0 

 21,5 



20.0 

 20c0 

 20.0 

 20.0 



