Growth in Striped Marlin — MORROW 
57 
metry, but again this is not significant. The 
measurements made by Gregory and Conrad 
also do not indicate significant allometry in 
the eye. 
It was not possible to measure the distance 
between the posterior edge of the eye and the 
pectoral base along the mid-line of the body 
with reasonable accuracy, so this measure- 
ment was made directly between the eye and 
the anterior margin of the pectoral base. This 
distance is distinctly isometric. Even though 
this is a slanted measurement, it is close 
enough to the mid-line so that, in combina- 
tion with the isometry of the sword length, 
it suggests that the relative length of the head 
also remains constant. 
When the length-weight relationship is 
isometric, as in the present example, the same 
condition is to be expected in depth and 
girth, for these two dimensions may be con- 
sidered as linear components of weight. One 
of the more obvious differences in body form 
between the striped marlin and the blue and 
black marlins is illustrated more simply by 
the isometry of these measurements than by 
the length-weight relationship. In the striped 
marlin, the equilibrium constants for depth 
and girth are 0.998 and 0.929, respectively. 
Shapiro (1938: 7) reports k = 1.45 for depth 
of body in the blue marlin. We have found 
no data on the black marlin, but Nichols and 
LaMonte (1941: 8) describe this species as 
"Heavier at larger sizes . . .," which certainly 
suggests positive allometry in depth and 
girth. Thus, the greater depth of the body in 
the blue and black marlins is reflected in the 
higher equilibrium constants. 
The length of the longest ray of the pec- 
toral fin shows slight negative allometry, with 
k = 0.707, P = 0.065. This slight negative 
allometry is not shared by either of the 
samples examined by Gregory and Conrad. 
The two flukes of the caudal fin were 
measured along their slant lengths from the 
anterior end of the corresponding peduncular 
keel to the tip of the longest ray. The tail is 
distinctly epibatic. The dorsal fluke is always 
slightly longer than the ventral, although 
there is a tendency in these adult animals for 
the tail to become more nearly symmetrical 
with greater size. Comparison of the two 
flukes shows that the dorsal fluke is nega- 
tively allometric with respect to the ventral 
fluke, with k = 0.843, Sk = 0.071, P<0.05. 
Thus, the rate of growth of the dorsal fluke 
relative to the rate of growth of the ventral 
fluke decreases as the gross size of the flukes 
increases. 
With respect to the standard length, both 
the dorsal and ventral moieties of the caudal 
fin exhibit highly significant degrees of 
negative allometry in this sample. For the 
dorsal fluke, k = 0.554, for the ventral fluke, 
k = 0.611. Both these values represent de- 
partures from isometry which are significant 
at P< 0.001. Thus, the rate of growth of the 
tail relative to the rate of growth of the fish 
as a whole tends to decrease rapidly with 
greater size in adult animals. 
It is interesting to compare these data on 
the tail with those derived from the measure- 
ments published by Gregory and Conrad 
{loc. cit.). Their group of 17 specimens from 
Cape Brett shows negative allometry in the 
lengths of the caudal flukes quite comparable 
to that reported here for fish from the same 
area. 
By contrast, their sample of nine fish from 
Mayor Island, some 175 miles to the south- 
east, exhibits positive allometry in both 
the dorsal and ventral flukes, although this 
allometry is of a low order of significance 
(P = 0.09 for the dorsal flukes and 0.04 for 
the ventral flukes). Nevertheless, there ap- 
pears to be a real difference between the two 
geographical groups as shown by a com- 
parison of the k values for the nine fish from 
Mayor Island and those of the 47 fish of the 
present sample from the vicinity of Cape 
Brett (P< 0.001). 
This suggests that the fish from Mayor 
Island and those from Cape Brett may repre- 
sent separate populations. However, this sug- 
gestion is put forward most cautiously, for 
