GilUchthys mirabilis — Barlow 
49 
TABLE 1 
Monthly Mean Air Temperatures 
PACIFIC 
SALTON 
GULF 
OF CALIFORNIA 3 
COAST 1 
SEA 2 
West Coast 
East Coast 
MONTH 
San 
Francisco 
37° 48'N 
San 
Diego 
32° 34'N 
33° 18'N 
Mulege 
26° 53'N 
La Paz 
24° 10'N 
Guaymas 
27° 55'N 
Topolo- 
bampo 
25° 36'N 
Mazatlan 
23° ll'N 
January 
93 
12.5 
12.0 
14.0 
18.2 
17.7 
18.6 
19.3 
February 
11.6 
13.5 
13.0 
16.0 
19.2 
18.9 
19.7 
19-4 
March 
12.9 
14.4 
17.5 
17.8 
21.3 
20.7 
20.1 
19.7 
April « 
13.4 
15.2 
20.5 
20.1 
23.2 
22.8 
22.2 
21.3 
May 
14.1 
16.9 
24.5 
22.9 
25.5 
25.5 
25.0 
23.8 
June 
14.9 
17.8 
28.0 
27.2 
27.2 
29.1 
29.1 
26.4 
July 
14.8 
19.9 
30.5 
30.5 
30.0 
29.8 
29.8 
27.5 
August 
15.1 
20.3 
31.5 
30.4 
30.3 
30.5 
29.7 
27.6 
September 
16.7 
19.4 
29.5 
29.0 
29.0 
30.2 
29.7 
27.5 
October 
15.7 
17.8 
24.5 
24.6 
27.0 
27.3 
27.8 
26.7 
November 
14.0 
15.9 
18.5 
19.5 
23.2 
22.6 
24.0 
23.5 
December 
10.4 
13.6 
13.0 
14.9 
20.0 
18.6 
19.7 
20.6 
Range 
7.4 
7.8 
19.0 
16.5 
12.1 
12.8 
11.2 
8.3 
1 Hubbs, 1948. 
2 Carpelan, 1958. 
3 Roden, 1958. 
Sea are surprisingly similar. The summer tem- 
peratures, in marked contrast, diverge greatly. 
San Diego and San Francisco remain moderate, 
but the mean air temperatures exceed 30 C in 
the Gulf and Salton Sea areas. 
The climate of the Salton Sea resembles that 
of the northern part of the Gulf of California. 
Both lie in the same climatological region, but 
the Salton Sea is a relatively small and shallow 
body of water surrounded by desert (Carpelan, 
1958). Consequently, its climate is even more 
extreme than that of the upper Gulf. 
Dispersal 
Pelagic larvae constitute the most likely ave- 
nues of genetic exchange between disjunct pop- 
ulations of mirabilis. The adults are closely 
restricted to their specialized and discontinuous 
habitats. At least some of the larvae must be 
swept out to sea where they could be distrib- 
uted to other bays by the oceanic currents. 
There is some evidence that the larvae of 
this genus are not adapted to a pelagic life as 
prolonged as those of the related genera, Quie- 
tula, Clevelandia, and llypnus (but not Eucyclo- 
gobius ). This conclusion is based on differences 
in postlarval pigmentation and behavior. Pelagic 
larvae and nektonic postlarvae characteristically 
are translucent with scattered melanophores, 
while the completely pigmented condition is 
found first in the benthonic stage. Postlarvae 
of GilUchthys mirabilis as small as 8-12 mm in 
length often are relatively heavily pigmented. 
At a comparable length, postlarvae of the other 
genera mentioned above are much more trans- 
lucent. 
Postlarvae of mirabilis in a slough in the 
northern Gulf of California, and at the Salton 
Sea, were seen to drift or swim into the current 
in slowly moving water. The postlarvae de- 
scended to the bottom and held station when 
the current strength increased. Postlarvae of 
Quietula guaymasiae Jenkins and Evermann 
were observed to form small groups that swam 
vigorously in a strong tidal current in the Gulf, 
darting from side to side at the surface in a 
manner reminiscent of young atherines; they 
seemed well adapted for life in open water. 
The larvae of GilUchthys mnabilis evidently are 
not dispersed as readily as are those of the re- 
lated genera just mentioned. 
