SPEARFISHES OF THE CENTRAL PACIFIC 



513 



10 



15 20 



PECTORAL LENGTH AS PERCENT OF FORK LENGTH 



25 



Figure 16. — Mean, standard deviation, and range of the ratio of length of pectoral fin to fork length in fish of more than 



200 cm. fork length. 



dorsal fins, those from the equatorial Pacific- 

 lower fins, and those from Hawaii the lowest. 



When height of the first dorsal fin is compared 

 with the greatest depth of the body we find a 

 marked allometric relationship (fig. 18). We 

 found no ampla in which the height of the first 

 dorsal was greater than the greatest body depth 

 and only one audax in which the height of the 

 first dorsal was less than 90 percent of the greatest 

 body depth. The trend lines are such, however, 

 that it is evident that in very small ampla the 

 first dorsal may exceed the greatest body depth 

 and in very large audax may be less than 90 

 percent. In any event, there is a considerable 

 overlap of specimens in which the anterior lobe is 

 between 90 and 100 percent of the greatest bod> 

 depth. 



The difficulty presented by allometric growth 

 and most of the overlap between ampla and audax 

 is eliminated if, instead of comparing the height 

 of the first dorsal with the greatest deptli of the 

 body, we compare it witii the heigiit of the first 

 anal (fig. 19). Plots of this relationship indicated 

 no allometric growth and hence the comparison 



by ratios is valid. This comparison shows that 

 the anal fin in audax averages 66 percent of tlie 

 height of the first dorsal, whereas in ampla it 

 averages 86 percent. If we accept 76 percent as 

 a dividing line between the species, we find only 

 a single overlapping specimen of audax with 

 a greater value. If<tiompax marlina is inter- 

 mediate with an average of approximatel}' 80 

 percent, and overlaps both of the other species. 



Despite the nearly isometric growth of the 

 anterior lobe, the middle of tiie first dorsal (as 

 indicated by the length of the 20tli ray) in audax 

 shows not merely negative allomet<-y but actual 

 negative growth, with those fish of less than 200 

 cm. fork length having a longer 20th ray than 

 the larger individuals. There is a suggestion 

 tliat the same condition pertains to ampla, but 

 the data are too few to verify it. At any rate, 

 tlie length of this ray changes little in fish of more 

 than 200 cm. and, hence, we compare the samples 

 on the basis of the actual average length of the 

 ray (fig. 20). Here we find the shortest 20th 

 rays in ampla and marlina and much the longest 

 in audax. This character appears to be a fairly 



