Figure 15.Color photograph of an aquarium specimen of the
large Amu-Darya shovelnose sturgeon, Pseudoscaphirhynchus
kaufmanni. These sturgeons are threatened due to environmen-
tal degradation in the region of the Aral Sea. Photograph courte-
sy of Boris Goncharov, Koltsov Institute of Developmental Biol-
ogy, Moscow.ciose and problematic taxon within Acipenseri-
formes (Figure 12). The fossil record ofAcipenser
has not helped phylogeneticists. Most described
fossil species are known only by fragmentary mate-
rial insufficient for differential diagnosis. There has
never been a comprehensive phylogenetic study of
the genus, no doubt due to its vast geographic range
and difficulties obtaining certain species for study.
The validity of several recent species, such asAci-
penser mikadoi is generally questioned, although
other evidence suggests that this species is distinct
fromA. medirostris(see Birstein et al. 1993,1997).
Many species ofAcipenser are endemic to eastern
Europe and Asia (Figure 13) and are poorly known
outside of this region. Traditional ideas about rela-
tionships withinAcipenser relied on biogeographyFigure 14.An interpretationofphylogenetic relationships within
Acipenserbased on Artyukhin (1995a and pers. comm.). This
tree is based on karyological data and biogeographic interpreta-
tion; this genus is in need of much additional study.
ger 1973). Sturgeons are also the subject of many
comparative anatomical treatments (e.g., Jessen
1972,1973) and much developmental research (e.g.,
Ginsburg&Dettlaff 1991, Dettlaff et al. 1993). Find-
eis (1997) described and reviewed skeletal anatomy
of extant sturgeons to make a cladistic analysis of
their interrelationships.
The genusHusoBrandt 1869 is known from two
extant species from Eurasia (Figure 10, 11). Com-
monly known as beluga,H. husois the largest fish to
enter freshwater, historically reaching lengths of 6
to 10 meters (Balon 1967, 1968, Pirogovskii et al.
1989, Barus∨&Oliva 1995). The kaluga,H. dauricus
inhabits the Amur River system, whereitis a target
of an aggressive fishery (Krykhtin & Svirskii 1997
this volume). Even as juveniles, these preferentially
piscivorous sturgeons target fish as prey. The status
ofHusoas a genus separate fromAcipenserwas un-
clear to many 19th century workers, who considered
it a subgenus ofAcipenser(e.g., Fitzinger & Heckel
1836). Recently, Jollie (1980) perpetuated this inter-
pretation, although since Brandt (1869), Berg
(1904), and Antoniu-Murgoci (1936a,b), it has been
easy to distinguish this genus. Findeis (1997) provid-
ed additional new characters separatingHusofrom
all other extant acipenserids. Unexpectedly, mole-
cular data given by Birstein et al. (1997) consistently
nestHusowithinAcipenser.
With 17 extant species,Acipenseris the most spe-
Figure 16. Color photograph of a captive reared specimen of the
common shovelnose sturgeon. Scaphirhynchus platorynchus
from the central United States.