48 
The preliminary manuscript was read by George 
A. Bartholomew, Henry W. Thompson, and 
John N. Belkin, all of the University of Cali- 
fornia, Los Angeles, and I thank them for their 
helpful suggestions. The research and writing 
were done under the supervision of Boyd W. 
Walker, and I am grateful to him for his guid- 
ance and aid. 
ECOLOGY AND NATURAL HISTORY 
The typical habitat of mirabilis is the inter- 
tidal coastal slough with its extensive mud flats. 
Less often it is a swampy lagoon, or slough, at 
the mouth of a dry river which most of the 
time is closed off from the ocean by a sand bar. 
Salinity 
The water in these habitats is of moderate to 
high salinity, hypersaline conditions being com- 
mon. The maximum salinity where mirabilis 
has been recorded was 82.5 %o at "El Marino,” 
north of San Felipe in the upper Gulf of Cali- 
fornia ( Lars Carpelan, personal communica- 
tion). The fish usually are absent where the 
water is fresh or only slightly brackish. Those 
kept in fresh-water aquaria were listless and 
died within 1-2 weeks, but this may have been 
due to the quality of the tap water. The activa- 
tion time of the spermatozoa is quickest in 
water having a salinity of 35 %o (Weisel, 1948: 
47). 
Temperature 
Aside from illumination, temperature is the 
one parameter of the environment to which 
it is related that changes more or less regularly 
with the latitude of the habitat. Local condi- 
tions, of course, may distort this temperature 
gradient. Furthermore, the Gulf of California 
has a climate different from that of the Pacific 
Coast. For these reasons, and in order to point 
out the extreme situation found at the Salton 
Sea, the meager temperature data available have 
been assembled and are presented in Table 1. 
Air temperatures have been used instead of 
sea surface temperatures. In the backwaters and 
ponds where mirabilis occurs, the surface water 
temperatures tend to be correlated with air tem- 
peratures (Carpelan, 1957: 376; Barlow, 1958: 
PACIFIC SCIENCE, Vol. XVII, January 1963 
582 ) , even when moderate tidal exchange takes 
place (personal observations). 
Throughout the year on the Pacific Coast, 
air temperatures increase from north to south. 
The increase is more pronounced in summer 
than in winter. For example, San Diego is 
warmer than San Francisco by about 4-5 C dur- 
ing the summer, but is only 2-3 C warmer in 
the winter. 
The protected Alviso ponds of southern San 
Francisco Bay, with their increased insolation, 
exhibit a special climatological situation (Car- 
pelan, 1957: 37 6) that removes them from the 
normal gradient of temperature change asso- 
ciated with latitude. Air temperatures at the 
ponds during 1 year averaged almost 7 degrees 
higher than the long-range monthly means for 
San Francisco shown in Table 1. The climate 
at Alviso ponds evidently is warmer than at 
many truly coastal sloughs much further south. 
In the Gulf of California region air tempera- 
tures increase from north to south during much 
of the year. But during the late, hot, summer 
season the situation is reversed and the mean 
air temperatures decrease, though only slightly, 
from north to south. However, the mean sea 
surface temperatures for August (Roden and 
Groves, 1959: 14) show no latitudinal trend 
whatsoever. Chiefly because of the reversal in 
the gradient of the air temperatures, the annual 
range of means is low in the south but is pro- 
gressively greater to the north in the Gulf. 
In the tidal sloughs of the Gulf of California 
where mirabilis normally is found, the summer 
increase from south to north in the range of 
water temperatures probably is augmented by 
the nature of the tidal change. The tidal range 
increases dramatically from south to north up 
the Gulf, reaching a maximum of 10 m at the 
head of the Gulf (Roden and Groves, 1959: 
28). The sills of the sloughs usually are high. 
Thus as one proceeds north in the Gulf, the 
sloughs daily have a progressively longer pond 
phase. This means that the buffering effect of 
the tidal exchange will be less, and as a result 
the water temperatures in the sloughs will reg- 
ister still greater fluctuations. 
The winter mean air temperatures at San 
Diego on the Pacific Coast, the central and 
northern Gulf of California areas, and the Salton 
