640 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 11. — Statistics describing regressions of body parts on standard length for ten-pounder leptocephali to juveniles 



Independent variable x 



Standard length. 



Do 



Do 



Standard length . 



Do 



Do 



Standard length. 



Do 



Do 



Standard length . 



Do 



Do 



Standard length . 



Do 



Do 



Standard length. 



Dependent variable y 



Head length.,. 



....do 



....do 



Eye diameter. 



....do 



....do 



Body depth... 

 ....do 



do 



Snout to dorsal fin. 

 do 



do. 



Snout to anal fin . . . 



do 



do 



Snout to pelvic fin. 



Stage of development 



Leptocephali 



Early metamorphic larvae 



Late metamorphic larvae to juveniles 



Leptocephali 



Early metamorphic larvae. 



Late metamorphic larvae to juveniles 



Leptocephali... ___ 



Early metamorphic larvae 



Late metamorphic larvae to juveniles 



Leptocephali ._ 



Early metamorphic larvae 



Late metamorphic larvae to juveniles 



Leptocephali 



Early metamorphic larvae 



Late metamorphic larvae to juveniles 

 Late metamorphic larvae to juveniles 



Specimen 



size range 



(mm.) 



5. 1-43. 3 



43. 3-26. 6 



25. 9-138 



5. 1-13. 3 



43. 3-26. 6 



25. 9-138 



5. 1^3 3 



43. 3-26. 6 



25. 9-138 



14. 3-13. 3 



43. 3-26. 6 



25. 9-138 



17. 3-43. 3 



43. 3-26. 6 



25. 9-138 



25. 9-138 



18.86 

 35.76 

 75.37 

 18.86 

 35.76 

 74.93 

 18.86 

 35.76 

 75.37 

 23.08 

 35.76 

 75.37 

 25.16 

 35.76 

 75.37 

 75.37 



1.94 

 3.05 

 22.40 

 0.42 

 0.64 

 5.27 

 0.96 

 1.75 

 11.11 

 19.68 

 29.42 

 40.07 

 23.55 

 32.80 

 57.94 

 40.13 



0.055 

 -.005 

 .294 

 .010 

 -.002 

 .069 

 .033 

 .003 

 .157 

 .809 

 .960 

 .505 

 .914 

 1.006 

 .756 

 .500 



0.892 



3.221 

 .261 

 .224 

 .689 

 .097 

 .336 



1.654 

 -.724 



1.015 

 -4. 898 



2.018 



.541 



-3. 161 



.934 



2.432 



Sy.x 



0.143 

 .178 



1.089 

 .035 

 .072 

 .492 

 .064 

 .144 

 .639 

 .133 

 .568 



1.027 

 .178 

 .382 



1. 148 



1.268 



S = mean of values of x 

 y = mean of values of y 

 N = number of specimens 



b = rate of increase of y 

 a = y-intercept of regression line 

 Sy.x=standard deviation from regression (standard error of estimate) 



Body depth at pectoral fin. — During the lepto- 

 cephalus period the body depth at pectoral in- 

 creases 0.033 mm. per millimeter increase of 

 standard length (fig. 27, table 11). During the 

 early metamorphic period it decreases 0.003 mm. 

 per millimeter decrease in standard length, and 

 during the late metamorphic period and juvenile 

 period to 138 mm. it increases 0.157 mm. per milli- 

 meter increase in standard length. The extension 

 of the regression line beyond 138 mm. appears to 

 fit the data for the larger sizes, suggesting the rela- 

 tion to be constant for the late metamorphic period 

 to adult. 



Snout to dorsal, fin. — During the leptocephalus 

 period the distance from snout to the origin of the 

 dorsal fin increases 0.809 mm. per millimeter in- 

 crease in standard length (fig. 28, table 11) . Dur- 

 ing the early metamorphic period it decreases 

 0.960 mm. per millimeter decrease in standard 

 length, a slightly higher rate of decrease than the 

 rate of increase in the leptocephalus period. Dur- 

 ing the late metamorphic period and to a juvenile 

 size of 138 mm., the rate of increase is 0.505 mm. 

 per millimeter increase in standard length. This 

 regression line extended beyond 138 mm. fits the 

 plot of measurements for larger specimens, sug- 

 gesting the relation to be constant for the late 

 metamorphic period to adult. The shifting of 

 the dorsal fin anteriorly during the early and mid- 

 metamorphic periods is evident when we compare 

 the distance from the snout to the dorsal fin for 

 specimens of similar size, 28 mm. standard length 

 for example, in various periods of development: 

 leptocephalus, about 24 mm. ; early metamorphic, 



about 22 mm.; and late metamorphic, about 16 

 mm. ( values are averages determined from regres- 

 sion line). 



Snout to anal fin. — During the leptocephalus 

 period the distance from the snout to the origin 

 of the anal fin increases 0.914 mm. per millimeter 

 increase in standard length (fig. 29, table 11). 

 During the early metamorphic period, it decreases 

 1.006 mm. per millimeter decrease in standard 

 length. During the late metamorphic period and 

 to a juvenile size of 138 mm., the increase is 0.756 

 mm. per millimeter increase in standard length. 

 As in the regression of snout to dorsal fin on 

 standard length, the extension of the regression 

 line beyond 138 mm. appears to fit the data for 

 larger sizes, suggesting a constant relation from 

 the late metamorphic period to adult. Shifting 

 of the anal fin anteriorly during the early and 

 mid-metamorphic periods is less than the shift of 

 the dorsal fin; for example, at 28 mm. standard 

 length, the distances from snout to anal fin are; 

 about 26 mm. for leptocephalus, about 25 for early 

 metamorphic larvae, and about 22 for late meta- 

 morphic larvae (averages determined from the 

 regression line). 



Snout to pelvic fin. — The pelvic fin is first dis- 

 cernible during the early metamorphic period, and 

 the plot of distances from snout to insertion of 

 pelvic on standard length indicates there is little 

 if any shifting of this fin during metamorphosis 

 ( fig. 30) . The slightly lower values for specimens 

 in the early metamorphic period, as compared 

 with those for late metamorphic larvae of similar 

 size, may indicate a slight shift posteriorly, or it 



