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<br />558 GREAT BASIN NATURALIST Vol. 42, No. 4
<br />DFf PFms OpF
<br />Pr
<br />VFf 1 MM PFmbr Eph St
<br />Fig. 5. Early prolarva of razorback sucker, Xyrauchen texanus; legend as in Figures 1 to 4 when applicable, and
<br />Eph = esophagus, OpF = opercular flap, Pfmbr = pectoral fin membrane, and PFms = pectoral fin musculatiirc.
<br />closed, yolk much reduced. Eye pigmentation
<br />completed, becoming black. Brown, stellate
<br />melanophores on ectoderm overlying mid-
<br />and hindbrain, and on paired dorsal pigment
<br />line, paired dorso-visceral pigment line (up-
<br />per body cavity), and unpaired midventral
<br />pigment line. No melanophores on horizontal
<br />myoseptum. Larvae swim to surface and feed
<br />on ground aquarium fishfood (TetraminR).
<br />Resting heart rate 120 beats per minute.
<br />Stage 32: late prolarva, day 10, 263 hours,
<br />9.0 mm (Fig. 6). Liver reaching midventral
<br />line; yolk largely assimilated. Pectoral fins
<br />0.8 mm long, no fin rays in any fin. Pigmen-
<br />tation increasing on dorsal, dorso-visceral,
<br />and midventral lines; melanophores on later-
<br />al pigment line, opercle, and at pectoral fin
<br />base.
<br />Postlarval Development
<br />Stages 33 and 34: assimilation of yolk, day
<br />12, 311 hours, 10.0 mm. Yolk assimilated,
<br />proctodeum open to form anus. Opercles
<br />cover two anteriormost gills. Otoliths present
<br />in auditory vesicles. Pectoral fins with 3 rays;
<br />caudal fin with 3 or 4 rays; no trace of dc,-sal
<br />or anal fins. Spleen forming posterior to 1<_,, ,.
<br />Posterior end of notochord (urostyle) VI,,_
<br />curved. Pigmentation increased on all as-.?a _zs
<br />except lateral pigment line; melanopr-sr _?s
<br />appearing on gas bladder.
<br />Stage 35: early postlarva, day 17,
<br />hours, 12.0 mm. Caudal fin-rays increase,
<br />7 to 9. Opercles cover gills. Median fin _i
<br />thickened and expanded at sites of anal .
<br />dorsal fins. Food materials in stomach; f< d ._,
<br />passing through intestine. All pigment:.,::';-
<br />excepting lateral pigment line intensified-
<br />Stage 36: dorsal and anal fin-ray r -
<br />ments, day 40, 960 hours, 15.5 mm (Fib .
<br />Fin-ray rudiments in dorsal and anal r
<br />caudal fin with full complement of oss
<br />rays. Gas bladder constricting into two cl_:=
<br />bers. Melanophores appearing on postf+r:-
<br />part of lateral pigment line.
<br />Stage 37: middle postlarva, day 48,
<br />hours, 20.0 mm. Rays of dorsal and anal
<br />partially ossified; pelvic fins rudimentary
<br />gatherings of mesenchyme; caudal fin bec':.
<br />ing emarginate. Gas bladder two chambe-
<br />Urogenital papilla apparent. Mouth termi.
<br />t 1mm
<br />GB Mp
<br />Pr PF L
<br />Fig. 6. Late prolarva of razorback sucker, Xyrauchen texanus; legend as in Figures 1 to 5 when applicable, .'.:i
<br />GB = gas bladder, L = liver, M = mouth, Mp = melanophores, and PF = pectoral fin.
<br />December 1982
<br />CFr
<br />AFr
<br />Fig. 7. Postlarva of ra:
<br />ures 1 to 6 when applica
<br />DPL = dorsal pigment 1
<br />= ventral pigment line.
<br />lips formed, small pa
<br />lower lips. Melanc
<br />body; ossified fin rah
<br />ment; larvae dark c
<br />trally and in eve reg.
<br />Stage 38: pelvic
<br />1200 hours, 20.8 mn
<br />form of small crescei
<br />Stage 39: pelvic
<br />hours, 23.5 mm. Pe
<br />thin membranous pa
<br />Stage 40: pelvic
<br />1536 hours, 27.0 mr
<br />ments within pelvic
<br />able. Dorsal and
<br />ossified. Mouth beg
<br />papillae highly deve
<br />Stage 41: ossificat
<br />70, 1680 hours, 32
<br />sified in pelvic fin.,
<br />persisting ventrally
<br />greatly reduced; do
<br />rated from caudal fii
<br />F
<br />
<br />
<br />
<br />
<br />
<br />
<br />Fig. 8. Late postlarva
<br />NF = nasal flap, P2F =
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