V I I . DESERT FISHES
457
ability is quite high among species and apparently among populations of
a given species. In many cyprinodontids, including pupfishes, a few eggs
are spawned each day over a period of days, and then a period of ovarian
repair and ovum production ensues, followed by subsequent spawning
throughout the breeding season (whenever that might be). A certain percentage of fish in many populations seem capable, on the basis of sizes
and morphology of their gonads, of producing gametes essentially throughout the year. In fact, some species and populations seem to have a pattern
perhaps far more refined and complex than that described before for
minnows.
In fluctuating environments, between 27° N latitude (Cuatro Ciénegas
basin) and 36°-37° N (Death Valley system), there seems to be about a
month's difference in timing of the overall sexual cycle of pupfishes. Some
Nevada pupfishes initiate breeding activities in marshes and shallower
pools in February, utilizing warm, marginal waters in midafternoon. Some
breeding activity continues throughout the seasons through mid-October.
Barlow (1961b) noted that males of the desert pupfish also "come
into nuptial colors and take up territories" in winter, as he observed on
February 11, in pools along the Sal ton Sea, California (latitude 33° N ) ;
their last observed spawn was also in October.
Cyprinodon atrorus begins sexual activities in late January in experimental ponds in Arizona (latitude 33° N ) , and in early January (in small
numbers) in its natural habitats of the Cuatro Ciénegas basin. That species
spawns as late as November, but no reproduction or breeding behavior
has been noted from early December through early January. Young of
C. atrorus are, however, produced every month of the year in experimental
ponds, and they also appear in some natural waters in midwinter. Sac-fry in
experimental ponds in December and early January may well have resulted
from delayed hatching of ova (Kinne and Kinne, 1962a) spawned in October or November and/or retarded growth rates of the young themselves
(Kinne, 1960).
Temperatures available to these fishes are similar in all areas discussed
above, according to our field data, with latitudinal effects being moderated
by higher altitudes at more southern localities. Day length therefore seems
to be a major factor in timing of their annual surges of reproduction.
Thermal springs provide a test of sorts for temperature versus day length
as primary stimuli for reproduction in fishes, since the constancy of the
former may suppress effects of the latter and allow year-round sexual activity. Miller (1948, 1950b, 1961b) and LaRivers (1962) suggested that
this was the case in some Death Valley cyprinodonts. Liu (1969), however, considered day-length control as a prevailing factor for reproduction
by stenothermous pupfishes and suggested that year-round reproduction
457
ability is quite high among species and apparently among populations of
a given species. In many cyprinodontids, including pupfishes, a few eggs
are spawned each day over a period of days, and then a period of ovarian
repair and ovum production ensues, followed by subsequent spawning
throughout the breeding season (whenever that might be). A certain percentage of fish in many populations seem capable, on the basis of sizes
and morphology of their gonads, of producing gametes essentially throughout the year. In fact, some species and populations seem to have a pattern
perhaps far more refined and complex than that described before for
minnows.
In fluctuating environments, between 27° N latitude (Cuatro Ciénegas
basin) and 36°-37° N (Death Valley system), there seems to be about a
month's difference in timing of the overall sexual cycle of pupfishes. Some
Nevada pupfishes initiate breeding activities in marshes and shallower
pools in February, utilizing warm, marginal waters in midafternoon. Some
breeding activity continues throughout the seasons through mid-October.
Barlow (1961b) noted that males of the desert pupfish also "come
into nuptial colors and take up territories" in winter, as he observed on
February 11, in pools along the Sal ton Sea, California (latitude 33° N ) ;
their last observed spawn was also in October.
Cyprinodon atrorus begins sexual activities in late January in experimental ponds in Arizona (latitude 33° N ) , and in early January (in small
numbers) in its natural habitats of the Cuatro Ciénegas basin. That species
spawns as late as November, but no reproduction or breeding behavior
has been noted from early December through early January. Young of
C. atrorus are, however, produced every month of the year in experimental
ponds, and they also appear in some natural waters in midwinter. Sac-fry in
experimental ponds in December and early January may well have resulted
from delayed hatching of ova (Kinne and Kinne, 1962a) spawned in October or November and/or retarded growth rates of the young themselves
(Kinne, 1960).
Temperatures available to these fishes are similar in all areas discussed
above, according to our field data, with latitudinal effects being moderated
by higher altitudes at more southern localities. Day length therefore seems
to be a major factor in timing of their annual surges of reproduction.
Thermal springs provide a test of sorts for temperature versus day length
as primary stimuli for reproduction in fishes, since the constancy of the
former may suppress effects of the latter and allow year-round sexual activity. Miller (1948, 1950b, 1961b) and LaRivers (1962) suggested that
this was the case in some Death Valley cyprinodonts. Liu (1969), however, considered day-length control as a prevailing factor for reproduction
by stenothermous pupfishes and suggested that year-round reproduction