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Freshwater Fishes of North
America 2000
Sample texts:
southern brook lamprey
Ichthyomyzon gagei Hubbs & Trautman, 1937
Family: Petromyzonidae
Although lampreys are eel-like in appearance, they are not particularly
closely related to eels, their ancient lineage instead betrayed
by several primitive anatomical features, most notably the absence
of jaws and a skeleton composed entirely of cartilage. The erroneous
vernacular epithet "lamprey eel" will, nevertheless,
likely persist in popular usage indefinitely. A comparably prevalent
misconception involves lamprey life history, derived from repeated
accounts of the parasitic feeding habits of the sea lamprey,
Petromyzon marinus Linnaeus, 1758, and its putative effect
on species held in higher regard by humans--in particular, trouts
and other salmonids. But although lampreys as a group have attained
a level of infamy as blood-sucking parasites, many species are
actually non-parasitic, having no significant ecological impact
on the species with which they share their stream habitats. I.
gagei's life history typifies that of all non-parasitic
lampreys: The individual exists for several years--in the case
of I. gagei, typically three years--as a filter-feeding
larva (known as an ammocoete) buried in the soft mud bottom of
its small stream. Upon metamorphosis to the non-feeding adult
form, it emerges from the substrate, living only long enough
to reproduce. This bizarre life history explains the absence
of adult specimens in native streams during all but the spring
spawning period. The Louisiana specimen pictured here underwent
its metamorphosis in captivity, emerging early one spring as
illustrated in this photograph, a ripe female turgid with eggs.
I. gagei is one of the smallest lampreys, growing
to only eight inches in adult length. Paradoxically, among the
non-parasitic forms, in particular, the characteristic changes
in morphology that accompany transformation to the adult stage,
along with the cessation of feeding and the physiological demands
imposed by rapid gonadal development, typically result in a net
reduction in both body weight and length in the transforming
individual, so that the maximum size for the larva may actually
slightly exceed that for the adult.
Salt Creek pupfish
Cyprinodon salinus salinus Miller, 1943
Family: Cyprinodontidae
While the pupfishes of the killifish genus Cyprinodon
collectively inhabit a diversity of habitats, the spring-dwelling
species of the American Southwest and Mexican deserts, in particular,
have fascinated students of piscine ecology because of their
ability to thrive in very hostile environments, exhibiting extreme
tolerance for variations in water temperature, salinity, and
levels of dissolved oxygen. The endangered Salt Creek pupfish
is endemic to McLean Springs and its outflow, Salt Creek, a saline
stream at approximately two hundred and forty feet below sea
level in the northern Death Valley basin. With air temperatures
frequently exceeding 120 F, conditions are especially harsh here,
and the stream may dwindle to a series of puddles and marshy
areas in summer, with pupfish population size varying in response
to these seasonal fluctuations in hydrology. Like other pupfishes
living in the Death Valley basin and its surroundings--and no
doubt in other areas as well--Salt Creek pupfish in isolated
pools have been observed to burrow into the oxygen-deficient
mud substrate under particularly unfavorable summertime conditions.
Although several species and subspecies of pupfishes inhabit
other springs and their outflows in Death Valley, no other fish
species inhabits Salt Creek. The nearby habitat of the Cottonball
Marsh pupfish, C. s. milleri La Bounty &
Deacon, 1972 (originally described as a distinct species), is
believed to have been separated from that of the Salt Creek pupfish
for only about two thousand years. While having diverged morphologically
in this relatively short span of time, these two subspecies have
retained comparable resistance to the hot, often hypersaline,
and poorly oxygenated waters in what are certainly two of the
most unlikely fish biotopes on earth. While prior taxonomic schemes
have contained all (oviparous) killifishes within the single
family Cyprinodontidae, this family is presently restricted to
a relatively few genera in South America (Orestias) and
Europe, North Africa, and the Middle East (Lebias), in
addition to Cyprinodon and a handful of smaller (mostly
monotypic) North American genera. Maximum length is approximately
two and a half inches.
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