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 5. Continued

18. Developing dorsal fin
1. with few (s5) or no melanophores.
2. with many (~6) melanophores.
19. Pigment in dorsal fin
I. present to extensive al6ng principal fin rays with few, if any, melanophores on membranes between principal rays (but might be present
on membranes between branches of rays).
2. extensive along principal fin rays and notably present (more than just a few melanophores) to extensive on at least a portion of
membranes between some or all principal fin rays.
20. Pigment in anal fin
1. absent.
2. present but very light with only a few (s5) melanophores (sometimes very linear along margins of rays and easily overlooked).
3. present but more prominent with many (~6) melanophores (sometimes very linear along margins of rays and easily overlooked).
21. Pigment in pectoral fin
1. absent.
2. present but very light with only a few (s 5) melanophores.
3. present but more prominent with many (~6) melanophores.
22. Pigment in caudal fin
1. present to extensive along principal fin rays with few, ifany, melanophores on membranes between principal rays (but might be present
on membranes between branches of rays).
2. extensive along principal fin rays and notably present (more than just a few melanophores) to extensive on most or at least the middle or
distal portion of membranes between some or all principal fin rays.
3. extensive along principal fin rays and notably present (more than just a few melanophores) to extensive only on proximal portions of
membranes between some or all principal fin rays.

between principal dorsal-fin and caudal-fin rays of all other metalarvae, except rarely in the
dorsal fins of white and flannelmouth suckers, are never pigmented with more than a few
incidental melanophores. Among other juveniles up to 40 mm SL, the membranes between
dorsal-fin and caudal-fin rays of all bluehead sucker and caudal-fin rays of all mountain sucker
and nearly all white and longnose suckers are similarly unpigmented.

Mouth characters. - Mouth characters are important in the diagnosis of adult
catostomids. Unfortunately the mouths are insufficiently developed in all but the latest larvae
and certain characters remain indistinct in the earliest juveniles (e.g., the lower lip lobes of some
bluehead sucker up to 25 mm SL, Table 6).
Mouth position remains terminal for some metalarvae and juveniles of mountain and
razorback suckers up to 25 mm SL, but changes to low terminal before the metalarval phase of
longnose and flannelmouth suckers and becomes low terminal or subterminal by 19 mm SL for
metalarvae of the remaining species. Some white, flannelmouth, and razorback suckers have
low terminal mouths throughout the metalarval phase and early juvenile period, at least up to 40
mm SL (Figs. 90-91). The first subterminal mouths appear as early as 18 mm SL for longnose
and bluehead sucker metalarvae and as late as 32 mm SL for razorback sucker juveniles. All
bluehead sucker juveniles and metalarvae over 19 mm SL have subterminal mouths (Figs.
47-49). Likewise for all mountain sucker greater than 25 mm SL, Utah sucker greater than 31
mm SL, and longnose sucker greater than 34 mm SL.
The median cleft of the lower lip divides the lip of these suckers into two distinct lobes.
The cleft is deep in most suckers but is shallow in bluehead and mountain suckers in which it is
bridged by a few rows of papillae. Once the lower lips are sufficiently formed to distinguish two
lobes, the lower lip lobes of most metalarvae and some juveniles of all species are well
separated. This separation continues for some Utah, white, and bluehead suckers up to 25 to 31
mm SL (Figs. 47 and 48), some razorback sucker up to at least 37 mm SL, and many mountain
sucker to at least 40 mm SL (Figs. 75-77). The gap between lip lobes closes much more rapidly

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