Gillichthys mirahilis — Barlow 
59 
Fig. 10. Correlation between population variances 
(±) of the first dorsal fin, and °N latitude. Open 
circle, Pacific Coast populations; closed triangle, Salton 
Sea population; closed circle, Gulf of California 
populations. 
of the samples represented by a single value 
in Figure 10 are heterogeneous, consisting of 
more than one year class. Similar dispersion 
in each year class, but about different means, 
would increase the apparent variation. 
Fin Ray Correlations 
The segmented rays of the dorsal and anal 
fins are positively correlated. When all the 
counts are combined, exclusive of the Salton 
Sea, the correlation coefficient is 0.603, signifi- 
cantly greater than zero. A positive correlation 
also is evident within and between year classes. 
The number of elements in the pectoral fin 
compared to that of the anal, and of the soft 
dorsal fin, reveals negative correlations, but only 
when means of different populations are com- 
pared ( Fig. 11). The correlation coefficient for 
the pectoral fin with the second dorsal fin is 
-0.737, and with the anal fin it is -0.659; both 
values differ significantly from zero. The data 
for the sample from San Felipe are shown in 
Figure 11 (the highest pectoral fin mean) but 
are not included in the computations of the 
correlation coefficients; as mentioned before, 
the counts are atypical. The inclusion of these 
counts does not affect the conclusion that the 
pectoral and median fin counts are significantly 
correlated. Data from samples from the Salton 
Sea also are not included. 
Fin Ray Index 
Probably the most useful statistic obtained 
from the fin counts is a derived index. The 
soft rays of the dorsal and anal fins are summed, 
then divided by the number of rays in the left 
pectoral fin and multiplied by 100. This index 
reflects the change in relationship between the 
fin ray numbers of pectoral and median fins at 
different latitudes (Fig. 12). 
On the Pacific Coast, not including San Fran- 
cisco and Venice, the index decreases progres- 
sively from north to south. In the Gulf of Cali- 
fornia the opposite is the case; the index in- 
creases to the south. The indices of Gulf and 
outer-coast populations consequently converge 
at low latitudes, being slightly higher in outer- 
coast populations. 
Noteworthy is the excellent agreement of 
index values for samples from Bahia Cholla and 
San Felipe, situated at similar latitudes but on 
opposite coasts of the Gulf. This is especially 
striking, considering that the San Felipe fish 
have unusually high atypical counts. 
The most revealing index is that of the Salton 
Sea population. It agrees with values obtained 
from samples taken in the vicinity of San Diego, 
the source of the Salton Sea stock. Further, the 
index is considerably higher than in any of the 
Gulf populations. 
n 
< io 
z 
< 
9 
19 20 21 22 23 
PECTORAL 
Fig. 11. Correlation between population means of 
number of pectoral fin rays, and number of segmented 
rays in the anal (closed circles) and dorsal (open 
circles) fins. 
