7343

• UCREFRP Catalog Number: 7343
• Author: Vanicek, C. D. and R. H. Kramer
• Title: Life History of the Colorado Squawfish,
• USFW Year: 1969
• Copyright Material: YES

VANICEK AND KRAMEH-SQOAWFISH AND CHOB LIFE HISTORY

AGE AND GROWTH
The scale method was used to determine
a~e and growlh of the Colorado squawfish
and the Colorado chub. Five or six scales
from each fish were placed between two glass
sl ides, moislened wilh water, 3nd enlar~ed
63x with a microprojector similar to that
described by Van Oosten, Deason, and Jobes
(]9.3~l). Annuli were formed in early June on
both species. Fish taken before June 1 had not
formed an annulus for thc currcnt year, but
all fish taken after July I had formed a new
annulus. If a fish had not formed an annulus
for the current year, the edge of the scale
was recorded 3S th3t year's annulus, Scales
11'('re not observed on fish shorler than 3S
mm lolal Icnglh. and the length at time of
scale formation for squawfish and chubs was
apparently between 3S and 1.0 mm. The IIse
of Ihe scalt~ method 10 determine age and
growlh was validated for hoth spccies hy use
of the criteria listed by Hile (19-J,]).

Colorado Squaw/ish

Scale samples from 132 squawfish were
analyzed for age and growth determinations,
Annuli were recorded from the laleral field
of the scale rather than from Ihe Illore com.
monly utilized anterior field since circuli in
Ihe anterior field were compressed, and an-
nuli were difficult to distinguish, The oldest
alld largest squawIish taken in this study was
all ll-year oJd femaJeGlO nlJll JOlIg weigh.
ing 2263 gillS.
The body.scale relationship was linear from
a scale radius of 23 mm to allOut no mm;
abovc this Jen~lh, huwen~r, the slope de.
creased and Ihe relationship was non.linear
(Figure 3), Therefore, the relationsllip was
described by two melhods. Frolll a scale
radius of 2.'1 10 110 mm. a linear regression
was filled hy Ihe llIt'lhod of least slJunn's:

L = :3.3 + 4,077 S

wlwrl' L = lolill IJOcI)' Jen~lh ill mjllimelers
and S = lateral scale radius X()g in millime-
ler!', For scale radii ahove 110 111111. a line was
filled by eye. A special nomo~raph for back-
calculatini! lengths was constructed after Car-
lander 3nd SlI1ilh (] 9.14), which fit the linear
relationship up to a scale radius of no 111111
and the non.linear pallern over llO llllll,

197

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--..l---___..Lu_______-1___..L______L--_, .J
50 100 ISO 200
LATeRAL SCALE RADIUS - MM IX6BI

FIl;UIlF. .l-llouv.scale rcblionship of CoJorauo
s'lnawfish, Green l{i, er.

Squawfish of all age ~roups from 0 to XI
were included in the age und growth analysis.
Mean total length at time of first annulus
formation was 44 mm, aud average annual
increment increased to 73 mill in the fifth
year, after which it decreased ( Tallie 3), No
difference in growlh hetween sexes was ob.
served,
A ""oodness of oTolI'lh" test similar to
o t" ,
that described by Hill' (J ()tl) , was performed
on 3ge groups I-VIII. Annual variation in
growth lI'as expressed as percentage deviation
from lllean annual increment for the 1958-
] ()6S pniod,alHl grlll",h raIl'S decrea!'ed
steadily (Table 4), In 19.')<J, the annual lenglh
increment was 19 percent above Ihe [l.year
average, while in 1965, it had (Iecreas/'il to
27 percent bdow tbe average,
Wilhin-season growlh of age groups 0-11
was described, Y oung-of.the-year squawfish
were 1110st numerous in seine collections 3
to 6 weeks after the estimalt'd sp3wning pe-
riod, and least COllllllon in fall collections,
Yearlings were most alm/lIlant in seine 1'01-