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Sturgeon Acipencer columbiaensis sp.nov.
David Stephen and Jeffery Goodman
9127 Paseo Grande Way, Elk Grove, California 95758, USA
davidstephen2004@yahoo.com
SUMMARY
The study provides morphological, osteological and biological evidences to separate the long-snout
sturgeons of the Snake River (Idaho, USA), Kootenai River (USA, Canada) and Nechako River
(Canada) from the taxonomic muddle of the White sturgeons identified as Acipenser transmontanus
(Richardson 1836). Based on these evidences a new species status is proposed for the long-snout
sturgeons and the scientific name Acipenser columbiaensis sp. nov. is given, along with common
name the Columbia Sturgeon. Whereas, the short-snout sturgeons in the Sacramento River
(California, USA), lower Columbia River System (USA and Canada) and lower Frazer River (British
Columbia, Canada) fit the original description of the type A. transmontanus (Richardson, 1836),
however, they show the distinguishing characters of the Genus Huso and hence a taxonomic revision
of its scientific name to Huso transmontanus (Richarson, 1836) is warranted. The proposed new
species status of the long-snout sturgeons has serious implications for recovery programs and given
the precarious condition of the natural stocks it is recommended that the new species A.
columbiaensis sp.nov. be placed on the endangered species list in Canada and the USA.
INTRODUCTION
There are twenty-one living species of sturgeons in the Genus Acipenser and these are distributed in
the Pacific and Atlantic Oceans, and the Caspian, Black and Adriatic Seas. The Genus Acipenser
(Linnaeus, 1758), is characterized by two salient features: branchiostegal membranes are joined
directly to the isthmus (joined to each other in the Genus Huso) and a transverse mouth cleft.
Additional distinguishing characters are the direct articulation of the palatoquadrate with the
symplectic and the posterior position of the stylohyal on the symplectic (Tatarko, 1936). Taxonomic
records show only two species of sturgeons in the Pacific coast of North America. These are the
White Sturgeon Acipencer transmontanus (Richardson, 1836), and the Green Sturgeon Acipencer
medirostris (Ayres). However, this report is focused on the taxonomic status of a distinct sturgeon
species of the Columbia River System that is found embedded in the taxonomic muddle of the so
called White Sturgeons of the Pacific coast of North America.
Based on comparative examinations, Stephen (2004) has shown that the White Sturgeon in the
Sacramento River (California, USA) is morphologically, osteologically and biologically distinct from
the White Sturgeon of the Snake River (Idaho, USA) and therefore warranted a generic level
taxonomic revision. The Sacramento River sturgeon hitherto identified as Acipencer transmontanus
(Richardson, 1836) shows joined branchiostegal membranes and therefore must be assigned to the
Genus Huso, and its scientific name revised to Huso transmontanus (Richardson, 1836). A new
common name, the Steluga, was given in keeping with the names of two sister species, the Beluga
and the Kaluga (see Stephen, 2004). There are morphologically similar sturgeons found in the Lower
Columbia River and Lower Fraser River (Canada), these are considered to be conspecifics of the
White Sturgeon found in the Sacramento River, Huso transmontanus (Richardson, 2004).
The sturgeon in question is the sturgeon found in the Snake River of Idaho. This sturgeon does not
match the original type specimen of Richardson (1836). Instead, Richardson’s original type specimen
collected off Vancouver, Canada matches the Huso (Acipenser) transmontanus type found in the
Sacramento River, lower Columbia River and Frazer River. Therefore, the Snake River sturgeon has
been misidentified as Acipenser transmontanus (Richardson, 1836) and has thus far remained
undescribed. The Snake River sturgeon shows all the characters of the Genus Acipenser and is
morphologically distinguishable and biologically distinct from another sturgeon of the same genus
also found in these waters, the Green Sturgeon Acipenser medirostris (Ayers). Therefore, a new
species status is proposed for the Snake River sturgeon and the scientific name, Acipencer
columbiaensis sp.nov. is given along with the common name, the Columbia Sturgeon. The new
species will be described in detail for taxonomic purposes in a subsequent publication. However, here
we compare the Steluga and the Columbia sturgeon to show the differences between these two
species belonging to two different genera. The purpose of this report is to bring to the immediate
attention of sturgeon research scientists and sturgeon farm operators that the so called White
Sturgeons of the Pacific coast of North America are actually composed of two species: an
Ascipenser represented by a new species A. columbiaensis sp. nov. and a Huso represented by Huso
transmontanus (Richardson, 1836).
MATERIALS AND METHODS
For this study, early fingerlings, yearlings and adults of the Snake River Sturgeon were obtained
from farms near Hagerman in Idaho; these are progenies of wild parents from the Snake River.
Whereas, adult wild sturgeons from the Sacramento River were captured up-river near Grimes
(Colusa, County), while early fingerlings and yearlings produced from wild parents caught from the
same river were obtained from farms in Sacramento County. All specimens were examined fresh.
For osteological purpose, specimens were boiled and bones were separated. An extensive search of
Internet sites of sturgeon fishing guide services yielded valuable information and photographic
evidences.
RESULTS AND DISCUSSION
It should be clear that apart from the Green Sturgeon Acipenser medirostris (Ayers), there are two
other sturgeons, the Columbia Sturgeon Acipencer columbiaensis sp.nov., reported here and the
Steluga, Huso transmontanus (Richardson 1836) in the Pacific coast of North America (Stephen,
2004) (Plate 1). The Columbia Sturgeon and the Steluga belong to two distinct Genera (Acipenser
and Huso respectively) and have easily distinguishable external generic characters and therefore it is
hard to explain why there has been such a protracted taxonomic oversight (Plate 2). The study by
Brannon et al, (1987) on the White Sturgeons of the Columbia River provides one explanation. They
noted variations in the shape of the snout and generally distinguished two types in the populations.
However, they presumed that the two snout types were in fact variants within the species Acipenser
transmontanus (Richardson, 1836). They attributed the differences in the distribution of the pointed
snout and the blunt snout populations in the Columbia River System to temperature variations, in
support of the rapid growth hypothesis proposed by Ruban and Sokolova (1986) for the Siberian
sturgeon Acipenser baeri. It was suggested that warmer temperatures during early development
increased growth rate and formed a blunt snout, whereas colder temperatures decreased growth rate
and formed a pointed snout. The acceptance of this hypothesis by subsequent researchers as well
may be the reason for the prevailing taxonomic error. The common name, White Sturgeon, has also
confounded the taxonomic problem hence the names Columbia Sturgeon and Steluga are given to
differentiate the two genera and species.
Based on an extensive review, it is clear that morphologically similar sturgeons found in the Kootenai
River (USA and Canada) and the Nechako River (upper Frazer River, British Columbia, Canada)
hitherto mistakenly identified as Acipenser transmontanus (Richarson) are conspecifics of A.
columbiaensis sp.nov. (Plate 3). It is hypothesized that these river-isolated populations of A.
columbiaensis sp.nov. in the Snake River (Idaho), the Kootenai River and the Nechako River once
formed a larger endemic interbreeding population because of connections between these rivers
following the last glacial retreat and the existence of a larger post-glacial Columbia drainage basin.
There are many species of freshwater fish that are common to these rivers and therefore lend
support to this theory (see McPhail and Lindsey, 1977). This may also explain the absence of A.
columbiaensis sp.nov. in the Sacramento River in California or further south.
There are many morphological, osteological, anatomical and behavioral differences between the
Columbia Sturgeon and the Steluga. It is beyond the scope of this report to elaborate all of them;
hence a few selected differences are presented here. We describe some unique and distinguishing
characters of the Columbia Sturgeon and compare it with the Steluga at three stages in their life
history.
The adult Columbia Sturgeon, Acipencer columbiaensis sp.nov. is distinguished by the long pointed
and slightly upturned snout; a flat crocodilian arrow head and a streamlined and tapering body form.
Whereas, the Steluga, Huso transmontanus (Richardson , 1836) has a short blunt snout and a turtle
shaped high forehead; the body form is bulky and rounded from the gills to the mid-section. Barbels
are placed closer to the mouth than to tip of snout in the Columbia Sturgeon, unlike the Steluga,
where the barbels are closer to tip of the snout (Plate 2: a, b; Plate 4: a, b). Mouth is relatively larger,
cleft is transverse with broad gelatinous lips that fold over the base; lower lip is centrally disrupted
with a narrow gap in the Columbia Sturgeon. Whereas, in the Steluga, lips are thin, tightly stretched,
lower lip centrally disrupted by a wider gap, mouth appears relatively smaller and is distinctly
crescentic in the juveniles and adults.
Bony anal scutes absent or appear as few cartilage buds or as faint markings in two diverging rows
from the anal fin base to the anal opening in the adult Columbia Sturgeon. In the juveniles and adults
of the Steluga, the bony anal scutes are prominent and appear in parallel rows (Plate 4: e, f, g, h). In
the Columbia Sturgeon, body coloration is golden brown or light grey and extends past the lateral line
to the ventral scutes; undersurface is white. Whereas, the coloration in the Steluga is greenish gray,
light gray or dark gray on the dorsal side, fading past the lateral line and has a white under surface.
In the adult Columbia Sturgeon, the dorsal scutes lie under the skin and are barely exposed; first
dorsal scute is smaller than the second and the two are articulating by means of finger like
crenulations and sharp projections on the anterior and posterior margins, scute surface is smooth,
slightly curved not keeled and shield shaped. Whereas in the adult Steluga, the first dorsal scute is
larger than second; dorsal scutes are all fully exposed with a rough pitted surface; margins smooth
not articulating, with sharp keel (Plate 5: e).
In the juveniles and adults, the distinctly long and pointed snout in the Columbia Sturgeon is
supported internally by an elongated triangular endochondral rostrum, and externally on the dorsal
surface by numerous and well separated bony shields that are arranged in a radiating fashion from
the tip of the snout to the clustered dorsal rostral bones at the base of the snout (Plate 4: a, b; Plate 6:
a; Plate 5: a, b, d). In the juvenile and adult Steluga, the endochondral rostrum is short and semi-
circular; there are few separated bony shields (some branched) on the short snout (Plate 6: a; Plate 5:
a, b, c). Among the many osteological and anatomical distinguishing characters, the ventral rostral
bone and the nature of attachment of the branchiostegal membranes are considered here. In the
fingerlings and juveniles (two years old) of the Columbia Sturgeon, the ventral rostral bone has the
posterior end articulating with the parasphenoid, while the anterior mid section has a patch of
dentition (pitted surface) and then it merges into staggered rows of numerous flat and elongated
bones that end in the tip of the snout; these bones probably fuse to form the single elongated
structure seen in the larger juveniles and in adults (Plate 5, e). Whereas in the Steluga, the ventral
rostral bone in the fingerlings and juveniles is a well-developed single bone with exposed dentition
throughout the structure and a single separated patch near the posterior end. In the adults, the
posterior end is distinctly triangular and webbed, with two pointed bases. The dorsal point articulates
with the parasphenoid while the ventral point hangs free. In the adults, this triangular webbed
process is very prominent while the anterior end is reduced and vestigial (Plate 5, e). In several
specimens of the Columbia Sturgeon, the ectopterygoid was fused to the dermopalatine on one side
only, but was separate from it on the other side (Plate 5: f). Interestingly, in Scaphirhynchus, the
ectopterygoid is fused to the dermopalatine, whereas they are separate elements in all other
Acipenseriformes according to Findeis (1997). Another anomaly seen in the parasphenoid of some
Columbia sturgeons are the presence of just one internal carotid foramen off the median line or none
at all, whereas in the Steluga there are two carotid foramina on either side of the median line (Plate 6:
b, c).
There are interesting differences in the nature of the attachment of the branchoistegal membranes
during the life history of the two sturgeons. In the fry to mid fingerling stage of both species, the
branchiosteal membranes are attached to each other and form a free fold over the isthumus (Plate 4:
f, g) this is the primary distinguishing character of the Genus Huso. Whereas, in the juveniles (one
year old Steluga; two years old Columbia sturgeon) of the both species, the branchiostegal
membranes are seen attached directly to the isthmus, which is the primary distinguishing character
of the Genus Acipencer (Plate 4: a, c, d) . In both these sturgeons, it appears that in the early
fingerling stage, the branchiostegal membranes recedes and becomes attached to the isthmus and this
may facilitate the benthic feeding mechanism. Apparently, the Steluga undergoes a change once again
and the branchiostegal membranes join each other and form a free fold over the isthmus probably in
the second or third year. This change is of evolutionary significance in the Huso and clearly sets this
Genus apart from the Acipensers. It is known that the larger juveniles (two to four year olds) and
adults of the Steluga are found in the lower-river and open bay or coastal waters. This change in the
Huso appears to be associated with pelagic life and piscivorous feeding behavior. Whereas, the
Columbia Sturgeon spends most of its life in the upper river stretches, where it is shallow and rapids
generate strong water currents. Its low profile streamlined body form is well adapted for these
conditions and for feeding on benthic organisms. It is also interesting that in the Columbia sturgeon,
the branchiostegal membranes in the juveniles and adults are circular and thin; they spread well over
the ventral pectoral girdle (Plate 2: c, d; Plate 4: b, c, d). This configuration facilitates sealing of the
gill chambers to develop suction pressure in the retractable tubular mouth as it opens downward for
effectively feeding on benthic organisms.
It appears that in the adult Huso, the free fold formed by the joining of the brachiostegal membranes
over the isthmus, the nature of articulation of the Meckel’s cartilage in the jaw and the torpedo body
form are three associated features that facilitate pelagic swimming and piscivorous feeding behavior.
The Steluga is known to feed aggressively on salmon in the Columbia River and on herring in the
Sacramento River Delta or the San Francisco Bay waters. This is similar to the behavior of the two
sister species, the Beluga and the Kuluga. Whereas, in the Columbia Sturgeon, the nature of
attachment of the branchiostegal membranes, the jaw articulation and tapering body form are three
associated features that are distinct and they support a benthic life. As mentioned earlier, the long
pointed snout and streamlined body form of the Columbia Sturgeon is well adapted for living in fast
water currents of upper river stretches. This requires constant swimming to maintain position. The
extensive lateral aerobic muscle (red meat) found in the fish supports this notion. Whereas, the adult
Steluga is pelagic with a torpedo body form and has less aerobic muscle. The ration of the red meat
to white meat in fillets of the two sturgeons clearly shows this difference (Plate 6: d, e, f). Another
interesting difference is seen in their eggs. The Columbia Sturgeon’s eggs are smaller, light grey or
greenish gold and have distinct light and dark bands around the animal pole, whereas the eggs of the
Steluga are larger and black or dark grey with a darker cap surrounding the animal pole (Plate 6; g).
This by no means exhausts the differences between these two sturgeons, but should suffice for the
scope of this report.
The Columbia River Basin is described as a Pleistocene Refugium and is considered as a source of
founder species for the Frazer River following the last glacial recession about 10,000 to 12,000 years
ago. It has been suggested that there were series of ephemeral connections into the upper Frazer,
Peace River and Mackenzie River drainages as slabs of continental ice continued to retreat (McPhail
and Lindsey, 1970). Nine of the native species are endemic to the Columbia Basin and this
distinguishes the fish fauna here from those of the North American Cordillera (McPhail and Carveth,
1992). The Columbia Sturgeon may have evolved as an endemic of the upper stretches of a larger
post-glacial Columbia River Basin and later fragmented following disconnections of tributaries. The
Kootenai River population (=A. columbiaensis sp. nov.) is said to have become isolated from other
sturgeons populations in the Columbia due to glacial alterations of the river 10,000 years ago (see
Brannon et al., 1987). Understanding the distribution and speciation of A. columbiaensis sp.nov., will
no doubt present some interesting challenges.
However, at present, all these river-isolated populations of the Columbia Sturgeon are also dam-
locked and it is assumed that being potamodromous they have been capable of some reproductive
success. Whereas, the Steluga spends most of its adult life in coastal waters as a pelagic fish, and
because it is anadromous, there is spawning failure in dam-locked populations in the Columbia River
System. However, large viable populations of the Steluga exist in the lower Frazer River, lower
Columbia River and the Sacramento River. There are many river-based and population-based
recovery programs for all sturgeons in the Columbia River System and the Frazer River System. It is
possible that cross-breeding of the short snout sturgeons (= Huso transmontanus Richardson 1836)
with the long snout sturgeons (A. columbiaensis sp.nov.) has taken place for improving the genetic
vigor by state and private hatcheries on the basis of an assumption that these sturgeons are
ecomorphs or separate stocks of the same species. These inter-generic hybrids may have been
stocked in natural waters under recovery programs, but confirmed hybrids are grow in a number of
farms. The adults of these hybrids show branchiostegal membranes attached to the isthmus as in
Acipenser, though narrowly; the snout is often intermediary in shape; the body form and external
characteristics are more like Huso transmonatnus (Richardson, 1836). The eggs of these hybrids
sometimes show a mix of characters of the two species in the same ovary. In view of the taxonomic
confusion elucidated here, recent studies on the genetics of the so called White Sturgeons need to be
sorted out because of the two species and hybrids involved in the natural populations and samples
sourced from farms. For example, Ludwig et al. (2001) are comparing chromosome numbers of
Huso transmontanus (= A. transmontanus, Richardson 1836) determined by van Eenennaam et al
(1989), while their microsatellite analyses is based on samples obtained from Kootenai River, which
is more than likely to be Acipenser columbiaensis sp. nov.
The three river-isolated populations of the new species Acipencer columbiaensis sp.nov in the Snake
River, Kootenai River and Nechako River are on the verge of extinction because of reproductive
failures due to confinement by dams and associated habitat alterations. In addition, sport-fishing
pressure has reduced these populations to a few thousands and recovery plans are inadequate
because they address an endangered “population,” not an endangered “species.” Federal, state and
local authorities regulate the river-isolated populations and dam-locked populations in these rivers as
endangered or protected populations of the White Sturgeon Acipenser transmontanus (Richardson,
1836; = Huso transmontanus, Richardson 1836). The White Sturgeon may not have been listed as an
endangered species because large viable populations of Huso transmontanus ( Richardson 1836) now
exist in the Pacific coast of North America. In view of the separation of the new species Acipencer
columbiaensis sp.nov, the Columbia Sturgeon from the populations of the Steluga, Huso
transmontanus (Richardson 1836), there is an urgent need to place the new species Acipencer
columbiaensis sp.nov. in the Endangered Species List in Canada and the USA. The follow up
publications shall contain detailed description of the new species, showing morphological,
osteological and anatomical characters, along with discussions on their distribution and speciation.
ACKNOWLEDGEMENTS
Preliminary discussions with several sturgeon specialists, especially Serge Doroshov, Joel Van
Eenennaam, Ron Bruch, Eric Findeis, Boyd Kynard and Eric Hilton was encouraging and are
gratefully recognized.
REFERENCES CITED
Brandt, J. F. and Ratzeburg, J. C.T., 1833: Medizinische Zoologie, oder getreue
Darstellung und Beschreibung der Thiere. die in der Arzneimittellehre in Betracht kommen, in
systematischer Folge herausgegeben. Medizinische Zool. i-iv + 1-364
Brandt, J. F., 1869: Mel. Bio. Acad. Sc. Petersbourg, VII, p 111 (type: Acipenser huso)
Brannon, E., Setter, A., Altick, J. and Miller, M., 1987: Columbia River White Sturgeon, Genetics
and Life History. Project No.1983 -31600, 88 electronic pages (BPA Report DOE/BP -18952-3),
Final Report.
Georgi, J.G., 1775: Bemerkungen einer Reise im russischen Reich in 1772 St, Petersburg. 2 vols.
Reise Russ. Reich. 1-920
Linnaeus, C., 1758; Syst. Nt., ed.X, p 237 (Type; A. sturio). Berg, Fauna Rossii, Ryby, I 911, p.
172.
McPhail, J. D. and Lindsey, C.C., 1977: Freshwater fishes of Northern Canada and Alaska. Fish.
Res. Board Canada, bulletin 137 -181pp
Richardson, J. 1836: The Fish. In: Fauna Boreali-Americana; or the zoology of the
northern parts of British Columbia; containing descriptions of the objects of natural history collected
on the late northern land expeditions under the command of Sir John Franklin. R. N. Fauna Boreali-
Americana I-xv + 1-327.
Ruban, G.I and L.I. Sokolov. 1986. Morphological variations of Siberian Sturgeon A.
baeri, in the Lena River in relation to its culture in warm waters. J. Ichthyol., 26(4):88-93.
Stephen, D. 2004. Discovery of the Genus Huso in the Pacific Coast of North America: The White
Sturgeon or Steluga: Huso transmontanus (Richardson, 1836) (manuscript)
Tatarko, K. 1936. Der Kiemendeckelapparat und seine Verbindung mit dem hyoid- und Kieferbogen
bei den Acipenseridae. Trav. Inst. Biol. Acad. Sci., Ukraine. 3: 5-67.
List of Figures
Plate 1: Three Sturgeons of the Pacific Coast of North America.
- The White Sturgeon or Steluga Huso (Acipenser) transmontanus (Richardson 1836);
adult, Sacramento River (California, USA); - Head of Steluga. Note: The short snout and position of barbels.
- Farm raised adult Columbia Sturgeon Acipenser columbiaensis sp.nov., offspring of parents
from the Snake River in Idaho. - Head of Columbia Sturgeon. Note: The long snout and position of barbels.
- Adult Green Sturgeon Acipenser medirostris (Ayres) from the Sacramento River (California,
USA). - Green Sturgeon. Note: Characteristic green strip and barbed anal scutes.
Plate 2: Snout Characteristics and Attachment of Branchiostegal Membranes
- The Columbia Sturgeon: Note position of barbells, mouth and lips
- The Steluga: Compare position of barbels, mouth and lips.
- The Columbia Sturgeon: Branchiostegal membrane attached to the isthmus.
- The Steluga showing branchiostegal membranes joined to each other and forms a free fold
- Close up of the free fold in the Steluga Columbia Sturgeon: Fingerling showing branchiostegal
membranes joined to each other and forming a free fold over isthmus. - Steluga: Fingerling showing branchiostegal membranes joined to each other and forming a free
fold over isthmus (fixed in formalin).
Plate 3: Conspecifics of Acipenser columbiaensis sp.nov (Type: Snake River, Idaho)
- Adult Acipenser columbiaensis sp.nov from Nechako River (BC, Canada)
- Farm raised adult Acipenser columbiaensis sp.nov; from parents of Snake River sturgeons.
- Adult Acipenser columbiaensis sp.nov from Kootenai River (Idaho and BC, Canada)
- Adult Acipenser columbiaensis sp.nov from Snake River.
Plate 4: Characteristics of Juveniles
- Above: Two years old Columbia Sturgeon. Below: One year old Steluga.Note: Compare snout
characteristics. - Same as above (4a): Compare snout characteristic; position of barbels and branchiostegal
membranes. - Columbia Sturgeon; same juvenile in item 4a: Branchiostegal membranes attached to isthmus.
- Steluga, same juvenile in item 4a: Branchiostegal membranes narrowly attached to isthmus.
- Steluga, same juvenile in item 4a: Well developed bony anal scutes
- Steluga, adult: Well developed bony anal scutes in parellel rows.
- Columbia Sturgeon, juvenile in item 4a; undeveloped anal scutes.
- Columbia Sturgeon, adult; undeveloped anal scutes, diverging rows
Plate 5: Dorsal Rostral Bones (DRB), Ventral Rostral Bones (VRB) and Scutes.
- Left: Adult Steluga; Right: Adult Columbia Sturgeon; skinned, DRB exposed.
- Above: Adult Steluga; Below: Adult Columbia Sturgeon; Note snout characteristics in
sectional cut. - Steluga has very few but larger dorsal rostral bones.
- Columbia Sturgeon with numerous dorsal rostral bones.
- Top Row: Steluga – Left to Right: Juvenile - first dorsal scute, second dorsal scute, VRB
single element showing exposed pitted surface, side view of VRB showing webbed posterior
end; Adult – VRB with enlarged webbed posterior end, first dorsal scute (larger); second
dorsal scute. Bottom Row: Columbia Sturgeon – Left to Right: Juvenile – first dorsal scute;
second dorsal scute; VRB multiple elements, smooth bones; Adult – VRB differs distinctly
from the VRB of Steluga, first dorsal scute (smaller), second dorsal scute. - Columbia Sturgeon: Ectopterygoid fused to dermopalatine.
Plate 6: Endochondral rostrum, parasphenoid and other characters
- Left: Steluga- one year old - endochondral rostrum (top is ventral view, bottom is dorsal
view); Right: Columbia sturgeon – two year old –endochondral rostrum (top is ventral view,
bottom is dorsal view). - Left: Steluga – one year old – parasphenoid (top is dorsal view, bottom- ventral view; Right:
Columbia Sturgeon – two year old – parasphenoid (top is dorsal view, bottom- ventral view). - Dorsal view, Top: Columbia Sturgeon – adult- parasphenoid; bottom: Steluga – adult -
parasphenoid - Columbia Sturgeon – cross section of fillet showing extent of aerobic muscle.
- Columbia Sturgeon – fillet showing extensive aerobic muscle under skin.
- Cross-section anterior of dorsal fin. Left: Steluga with thin layer of lateral aerobic muscle;
Right: Columbia Sturgeon with thicker layer of lateral aerobic muscle. - Formalin fixed - Left: egg of Columbia Sturgeon; Right: egg of Steluga