7723

• UCREFRP Catalog Number: 7723
• Author: Snyder, D. E. and R. T. Muth
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1990
• Copyright Material: NO

(Table 7, Fig. 7). Beyond 20 mm SL, fontan-
elle length increases proportionately with
body length, but width and shape vary with
species. Width generally increases in razor-
back sucker and maintains a more-or-Iess
oval shape, decreases in mountain sucker, and
remains relatively constant in the others
(greatest in Utah sucker and least in blue-
head sucker). For specimens 35-46 mm SL,
fontanelle width remains greater than 45%
of length in most razorback sucker (rarely as
low as 43%), drops to less than 25% in
mountain sucker, and ranges between 25 and
45% in the others (generally lowest in blue-
head sucker). Observations for Utah sucker
may be suspect due to poor culture condi-
tions and growth rates (Appendix C, Snyder
and Muth 1988).
Adult descriptions of the subject species
reveal that the fontanelle is significantly
reduced or lost only in bluehead and moun-

tain suckers. Smith (1966) reported that the
fontanelle of bluehead sucker is usually
reduced in juveniles and closed in adults,
while that of mountain sucker adults is usu-
ally reduced to a narrow slit but occasionally
obliterated. To document, preliminarily,
changes in fontanelle shape and size toward
the adult condition, we cleared and stained
one 76 to 81 mm SL yearling for each species
except Utah sucker (specimen not available).
Based on these solitary observations (Table
7), the fontanelle continues to grow in both
length and width in razorback sucker and
maintains its larger width-to-length ratio
(45%). The fontanelle increases significantly
only in length for white, flannelmouth, and
bluehead suckers, resulting in decreased
width-to-length ratios (25-26% for white and
flannelmouth and 19% for bluehead sucker).
Only in mountain sucker was the fontanelle
closed. More yearling and older specimens

Table 7. Comparison of frontoparietal fontanelle size for selected length groups of larval and juvenile
catostomids of the Upper Colorado River Basin. "N" is number of specimens examined.
Size group Catostomus Catostomus Catostomus Catostomus Catostomus Xyrauchen
Character ardens commersoni discobolus latipinnis platyrhynchus texanus
17-19 mm SL, n 2 2 4 3 0 3
Width, rnm 1.0-1.2 0.8-1.0 0.6-0.9 0.8-1.2 1.0-1.2
Length, mm 2.0-2.2 2.0-2.2 1.4-1.8 1.2-2.0 1.7-1.9
Width/length, % 45-60 4045 41-50 50-67 59-63
20-21 mm SL, n 1 2 2 3 2 5
Width, rnm 0.9 0.6-0.8 05-0.9 0.6-0.7 0.6-0.8 1.0-1.3
Length, rnm 2.1 1.9-2.1 1.7-1.7 1.8-2.0 2.2-2.2 1.8-2.1
Width/length, % 43 32-38 29-35 33-35 27-36 52-68
22-25 mm SL, n 2 1 3 3 1 2
Width, mm 0.9-0.9 0.8 05-0.8 0.8-0.8 0.7 1.0-1.3
Length, mm 2.3-2.4 2.0 1.3-2.8 1.8-2.1 2.2 1.9-2.1
Width/length, % 38-39 40 29-38 38-44 32 53-62
26-34 mm SL, n 3 2 2 2 1 2
Width, rnrn 1.0-1.0 0.8-0.8 0.6-0.7 0.7-0.8 05 0.9-1.3
Length, rnrn 2.3-2.4 2.3-2.6 2.0-2.2 2.2-2.3 2.1 2.1-2.3
Width/length, % 42-43 31-35 27-35 30-36 24 43-57
35-46 rnm SL, n 1 1 1 1 2 3
Width, rnm 1.1 0.9 0.7 0.7 0.4-05 1.1-1.7
Length, mrn 2.7 3.0 2.7 2.3 25-2.7 2.3-3.4
Width/length, % 41 30 26 30 15-20 48-50
All 22-46 mm SL, n 6 4 6 6 4 7
Width, rnrn 0.9-1.1 0.8-0.9 05-0.8 0.7-0.8 0.4-0.7 0.9-1.7
Length, rnrn 2.3-2.7 2.0-3.0 1.3-2.8 1.8-2.3 2.1-2.7 1.9-3.4
Width/length, % 38-43 30-40 26-38 30-44 15-32 43-62
76-81 rnrn SL, n 0 1 1 1 1 1
Width, rnm 0.8 0.7 1.0 0.0 2.3
Length, mm 3.1 3.7 4.0 0.0 5.1
Width/length, % 26 19 25 0 45
33