9492

• UCREFRP Catalog Number: 9492
• Author: Snyder, D. E.
• Title: Computer-Interactive Key to Sucker Larvae and Early Juveniles of the Upper Colorado River Basin with Description of Longnose Sucker.
• USFW Year: 2003.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

Table 7. Comparison of frontoparietal fontanelle size for selected length groups oflarval and juvenile catostomids
of the Upper Colorado River Basin. "N" is number of specimens examined.
Size group Catostomus Catostomus Catostomus Catostomus Catostomus Catostomus Xyrauchen
Character ardens catostomus commersoni discobo/us /atipinnis p/atyrhynchus texanus
17-19mmSL,n 2 2 2 4 3 0 3
Width, mm 1.0-1.2 1.5-1.5 0.8-1.0 0.6-0.9 0.8-1.2 1.0-1.2
Length, mm 2.0-2.2 1.8-2.1 2.0-2.2 1.4-1.8 1.2-2.0 1.7-1.9
Width/length, % 45-60 71-83 40-45 41-50 50-67 59-63
20-21 mm SL, n I 2 2 2 3 2 5
Width, mm 0.9 1.5-1.7 0.6-0.8 0.5-0.9 0.6-0.7 0.6-0.8 1.0-1.3
Length, mm 2.1 2.0-2.1 1.9-2.1 1.7-1.7 1.8-2.0 2.2-2.2 1.8-2.1
Width/length, % 43 75-79 32-38 29-35 33-35 27-36 52-68
22-25 mm SL, n 2 3 1 3 3 1 2
Width, mm 0.9-0.9 0.9-1.5 0.8 0.5-0.8 0.8-0.8 0.7 1.0-1.3
Length, mm 2.3-2.4 2.1-2.3 2.0 1.3-2.8 1.8-2.1 2.2 1.9-2.1
Width/length, % 38-39 39-68 40 29-38 38-44 32 53-62
26-34 mm SL, n 3 3 2 2 2 I 2
Width, mm 1.0-1.0 1.1-1.4 0.8-0.8 0.6-0.7 0.7-0.8 0.5 0.9-1.3
Length, mm 2.3-2.4 2.7-3.0 2.3-2.6 2.0-2.2 2.2-2.3 2.1 2.1-2.3
Width/length, % 42-43 40-47 31-35 27-35 30-36 24 43-57
35-46 mm SL, n 1 2 1 1 1 2 3
Width, mm 1.1 1.1-1.4 0.9 0.7 0.7 0.4-0.5 1.1-1.7
Length, mm 2.7 3.2-3.8 3.0 2.7 2.3 2.5-2.7 2.3-3.4
Width/length, % 41 29-44 30 26 30 15-20 48-50
All 22-46 mm SL, n 6 8 4 6 6 4 7
Width, mm 0.9-1.1 0.9-1.5 0.8-0.9 0.5-0.8 0.7-0.8 0.4-0.7 0.9-1.7
Length, mm 2.3-2.7 2.1-3.8 2.0-3.0 1.3-2.8 1.8-2.3 2.1-2.7 1.9-3.4
Width/length, % 38-43 29-68 30-40 26-38 30-44 15-32 43-62
47-75 mm SL, n 2
Width, mm 1.1-1.4
Length, rnm 3.8-4.5
Widthllength, % 29-31
76-81 mm SL, n 1 I 1 1 1 1
Width, rnm 1.5 0.8 0.7 1.0 0.0 2.3
Length, mm 4.8 3.1 3.7 4.0 0.0 5.1
Width/length, % 31 26 19 25 0 45

longnose and Utah suckers and least in bluehead sucker). Observations for Utah sucker may be
suspect due to poor culture conditions 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 mountain suckers. Smith (1966) reported that the fontanelle of
bluehead sucker is usually reduced in juveniles and closed in adults, whereas that of mountain
sucker adults is usually reduced to a narrow slit and only occasionally obliterated. To
preliminarily document 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 all other species except
mountain sucker, resulting in decreased width-to-length ratios (31 % for longnose sucker,
25-26% for white and flannelmouth suckers, and 19% for bluehead sucker). Only in mountain
sucker was the fontanelle closed. More yearling and older specimens must be examined to
determine if fontanelle closure is typical of mountain sucker populations in the UCRB.

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