7146

• UCREFRP Catalog Number: 7146
• Author: Hubbs, C. L. and R. R. Miller
• Title: Hybridization in Nature Between the Fish Genera
• USFW Year: 1953
• Copyright Material: YES

2b~

Hubbs and Miller

INTEHMEDIACY OF HYBRIDS

All eight specimens agree with fish hybrids in general (Hubbs,
1940, pp. 205-9) in being intermediate between the inferred parental
species in nearly all differential characters, both of meristic counts
(Tables II-IV) and measurements (Table V; Figs. H2).
Meristic counts.-In number of scales, as represented by t.he
lateral-line count (Table II), the hybrids are extraordinarily varia-
ble, and for this reason do not appear to represent a taxonomic unit.
The counts are 72, 81-86, and 1l0-a surprising coverage, of 89,
lor only eight specimens. Two of the eight counts are beyond the
wieldy separated means of the two parent species, though the average

TABLE II

NUMBER OF SCALES ALONG THE LATERAL LINE IN CATOSTOMUS,
HYBR!!JS, AND XYR.~UCHEN

:
Lateral-line scales
Locality and form
No. Range Mean =i= S
Upper Colorado River system
Catostom1ls latipinnis . . . . . . . 48 90-116 103.02 =i= 1.
Hybrids. . . . . . . . . . . . . . . . . . 8 72-11 0 85.25 =i= 3.
Xyrauchen texanus . .. . . . . . . 12 69-85 77.61 =i= 1.
Gila River system
Catostomusinsignis . . . . . . . . 13 58-65 61.00 =i= O.
Hybrids. . . . . . . . . . . . . . . . . . 6 62-71 66.50 =i= 1.
Xyrauchen texan1ls .,. . . . . . . 13 68-87 75.85 =i= 1.
- :

E

03
86
32

64
41
45

is e1dinitely intermediate. In the dorsal-ray count (Table III) the
hyh'ids are intermediate on the average but approach Catostomus
lalil'innis more closely, and all the counts fall within the range for
that species. The lower number of rays in the species of Catostomus
seems to be imperfectly dominant. The gill raker counts (83, 34, 34,
87, :18, 88, 38, and 88) all fall between the limits of variation for the
counts of the parental species (25-32 for C. latipinnis; ,H-50 for
X. t,~xanus) (Table IV).
Jfeasurements.-In differential measurements the eight hybrids
are rather consistently intermediate (Table V). Since the hybrids
vary greatly in size (102, 2.".i6, 379, 384-386, 391, and 44,2 mm. in

I,

Hybridization between Catostomus and Xyrauchen

213

. .

TABLE III
NUMBER OF DORSAL RAYS IN CATOSTOMUS, HYBRIDS, AND XYRAUCIIEN

Principal dorsal rays
Locality and form
1011 12 13 14 15 16 No. Range Mean =i= SE
-
Upper Colorado River system
Catostom1ls latipinnis . . . . . 1 16 116 56 2 . . . . 191 10-14 12.22 =i= .05
Hybrids . . . . . . . . . . . . . . . . . . . . 3 4 1 . . . . 8 12-14 12.75 =i= .25
X yrauchen texanus . . . . . . . . . . . " . . . 8 2 2 12 14-16 14 . 50 =i= .23
Gila River system
Catostomus insignis . . . . . . . . . 2 8 3 . . . . . . 13 11-13 12.08 =i= .18
Hybrids . . . . . . . . . . . . . . . . . . . . 3 3 . . . . . . 6 12-13 12.50 =i= .22
Xyrauchen texanus . . . . . . . . . . . .. . 210 4 1 17 13-16 14.24 =i= .18

TABLE IV
NUMBER OF GILLRAKERS IN CATOSTOMUS, HYBRIDS, AND XYRAUCHEN
The counts were made on the first arch (both limbs) of the leFt side and include
rudiments. For the upper Colorado River system only specimens more than 100
mm. in standard length were included, as COUBtS indicated that the raker number
becomes fixed at about that size. The material from the Gila River system com-
prises specimens from 52 to 79 mID. long.

Gillrakers on first arch
Locality and Form ,
No. Range Mean =i= SE
Upper Colorado River system (adults)
Catostom1ls latipinnis . . . . . . . . . . . . . . . . . . . 48 25-32 26.92 =i= 0.21
Hybrids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 33-38 36.25 =i= 0.77
Xyrauchen texanus . . . . . . . . . . . . . . . . . . . . . 11 44-50 47.36 =i= 0.14
Gila River system (young)
Catostomusinsignis ................... . 25 24-30 26.16 =i= 0.30
Hybrids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 28-36 30.83 =i= 1.14
Xyrauchen texanus . . . . . . . . . . . . . . . . . . . . . 13 36-43 39.92 =i= 0.64

standard iength) and since the proportional measurements of suckers
vary greatly with age, the expected average sizes of the parts for
the parental species were determined graphically (Figs. 1-2). Since
X yrauchen is very poorly represented in collections and seems to