A study of scales from known-age trout
by William Alvord
A THESIS Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree
of Master of Science in Fish and Wildlife Management
Montana State University
© Copyright by William Alvord (1953)
Abstract:
A total of 1055 scale samples from tagged, recaptured brown trout, rainbow trout, and eastern brook
trout; and 129 scale samples from planted, marked rainbow trout were taken from Prlckley Pear Creek,
Montana, between June, 1949, and October, 1951. In addition, 69 scale samples were obtained from
rainbow trout planted as fry In Savage Lake, Montana, and 42 scale samples were secured from
known-age rainbow trout brood stock at the U.S. Fish and Wildlife Service Fish Hatchery, Ennis,
Montana. Studies of these scales substantiated the scale method of aging wild trout and trout planted as
fry or young-of-the-year fingerlings.
Marks which may have been caused by shocking, handling, and tagging were present on some scales
from Prickley Pear Creek, but they did not occur with any uniformity or regularity.
Scales from the known-age rainbow trout brood stock had "annuli" in varying numbers and positions
on fish of the same age. These "annuli" did net conform to the known age of the trout and were
probably caused by the hatchery feeding practices and handling during spawning operations.
Annuli beyond the third were, in general, in closer proximity to one another and were more difficult to
interpret. In many instances, erosion or absorption obliterated scale characters on the scales of older
fish.
Annulus formation had been completed in 74,8 percent of the brown trout and 89.3 percent of the
rainbow trout by the latter part of June in 1950. In 1951, 72.3 percent of the brown trout and 78.6
percent of the rainbow trout had formed new annuli by the second week in July. The failure of some
trout to form new annuli during the period of annulus formation was almost always associated with
little or no gain in total length. k' 7 7 *
AU 7
A STUDY OF SCAIES FROM KNOWN-AGE TROUT
by
*
WILLIAM ALVORD
A TlffiSIS
Submitted to the Graduate Faculty
in
p a r t ia l fu lfillm e n t o f the requirem ents
fo r t h e degree o f
Master o f S cience i n F ish and W ild life Management
at
Montana S ta te C o lleg e
Approved;
_________ J . H. Pepper
Head, Major Department
______ C. J . D, Brown_________
Chairman, Examining Committee
__________J . A. Nelson
Dean, Graduate D iv is io n
Bozeman, Montana
January, 1953
2
Table o f Contents
A b s t r a c t .................................. ..... ..............................................................................3
I n t r o d u c t i o n .................................................... .....................................................4
Sources o f s c a le
samples .
.
.
.
.
5
Methods .............................................................................................................. 7
S cale ch aracters on"known-age"
w ild t r o u t ................................................. 9
E ffe c ts o f shocking, h an d lin g, and taggin g o f tro u t on th e ir
s c a le c h a r a c t e r s ...............................
18
S cale ch aracters o f hatchery r a ise d tr o u t plan ted in
P r ic k le y Pear Creek ............................................................................................. 18
S cale characters o f rainbow trou t plan ted in Savage Lake . . .
20
S ca le characters o f the Ennis Hatchery rainbow tro u t
21
Acknowledgements
Summary
.
.
.
.
.................................................................................................. 21
.................................................................
L itera tu re C i t e d ........................................................................
. . 2 2
.
.
.
.
25
136924
3
A b str a ct
A t o t a l o f 1055 s c a le samples from tagged, recaptured brown tr o u t,
rainbow tr o u t, and e a ste r n brook tr o u t; and 129 s c a le samples from p la n te d ,
marked rainbow tro u t were taken from P r ic k le y Pear Creek, Montana, between
June, 1949, and October, 1951. In a d d itio n , 69 s c a le samples were o b ta in ­
ed from rainbow tro u t p lan ted as fr y in Savage Lake, Montana, and 42 s c a le
samples were secured from known-age rainbow tro u t brood sto c k a t the U. S.
F ish and W ild life S erv ice F ish Hatchery, E nnis, Montana. Studies o f th ese
s c a le s su b sta n tia te d the s c a le method o f aging w ild tr o u t and tro u t p la n ted
as fr y or yo u n g -o f-th e-y ea r f in g e r lin g s .
Marks which may have been caused by shocking, h an d lin g, and tagging
were p resen t on some s c a le s from P r ic k le y Pear Creek, but they did not
occur w ith any u n iform ity or r e g u la r ity .
S ca les from the known-age rainbow tr o u t brood sto c k had "annuli" in
varying numbers and p o s itio n s on f i s h o f the same a g e . These "annuli"
d id not conform to the known age o f th e tr o u t and were probably caused
by the hatchery feed in g p r a c tic e s and handling during spawning o p e r a tio n s.
Annuli beyond the th ir d w ere, in g e n e r a l, in c lo s e r proxim ity to one
another and were more d i f f i c u l t to in t e r p r e t. In many in s ta n c e s , e r o sio n
or ab sorp tion o b lite r a te d s c a le ch a ra cters on the s c a le s o f older f i s h .
Annulus form ation had been completed in 74.8 percent o f the brown
tr o u t and 8 9 .3 p ercen t o f the rainbow tr o u t by the la t t e r p art o f June in
1950. In 1951, 7 2 .3 percent o f the brown tro u t and 7 8 .6 percent o f the
rainbow tro u t had formed new an n u li by th e second week in J u ly . The f a i l ­
ure o f some tr o u t to fo ra new a n n u li during the period o f annulus form ation
was alm ost always a s so c ia te d w ith l i t t l e or no g a in in t o t a l len g th .
4
In trod u ction
W hile th ere have been numerous in v e s tig a tio n s made on the age and
growth o f f is h e s in both Europe and America, few c r i t i c a l s tu d ie s o f the
s c a le method have appeared, p a r tic u la r ly in America.
Van Oosten (1941)
recogn ized the lack o f such s tu d ie s and s ta te d th a t in over 150 papers,
o n ly some h a lf dozen gave a c r i t i c a l e v a lu a tio n o f the s c a le method.
S tu d ies made on age and growth o f tr o u t in t h is country include
th o se o f A pplegate (1947) who secured s c a le s from known age lake tr o u t,
G ristivom er n . namaycush. and Cooper (1951) who used tagged w ild brook
tr o u t, S a lv elin u a f o a t i n a l i s . to s u b s ta n tia te the s c a le method fo r f is h
more than three years o ld .
Van Oosten (1923) stu d ied the s c a le s from
known-age w h it e f is h e s , Coreaonua clu p eaform js. and Brown (1943) made a
study o f known-age g r a y lin g , ThymaI Ius s I q n if e r .
This study concerns the ch aracters on the s c a le s taken from known-age
tro u t.
The o b je c tiv e s were: to provide a check on the s c a le method o f
aging w ild tr o u t; to determine what e f f e c t shocking, h an d lin g, and tagging
o f tro u t might have on s c a le ch aracters; to determine whether hatcheryr a is e d tr o u t, p lan ted a t d if fe r e n t se a so n s, showed p e c u lia r or v a ria b le
s c a le ch a ra cters; and to study the s c a le characters o f hatchery brood
sto c k h eld a t more or le s s constant tem peratures.
Known-age f i s h , in t h is r ep o rt, in clu d es both w ild and hatchery
tro u t.
Since the a c tu a l hatching d a tes o f the w ild tr o u t were not known,
the term, "known-age", i s app lied to th a t p o rtio n o f th e ir liv e s between
the f i r s t capture and subsequent r ec a p tu r es.
The in te r v a ls between
5
captures ranged from approxim ately one to 26 months, and some f is h were
recaptured as many as f iv e tim es.
The s p e c ie s stu d ied were: brown tr o u t, Salmo t r u t t a ; rainbow tr o u t,
Salmo g a ir d n e r ii; and e a ste r n brook tr o u t, S a lv e lln u s f o n t l n a l l s .
Sources o f s c a le samples
A ll s c a le samples from known-age w ild tro u t were ob tain ed from f i s h
captured in con ju n ction w ith a f i s h p op u lation and movement study ca rried
out by the Montana F ish and Game Department on P rick ley Pear Creek, Lewis
and Clark County, Montana, (S te fa n ic h 1 9 5 2 ).
A rath er com plete des­
c r ip tio n o f the study area i s g iv en in the population and movement report
and w i l l not be rep eated h ere.
S cale samples to t a lin g 1055 were taken
from recaptured w ild tr o u t during the p eriod from June, 1949, to October,
1951, (Table I ) .
Table I
Number o f tim es tro u t were recaptured a fte r the f i r s t ta g g in g .
Sp ecies
Brown
Rainbow
Brook
T o ta ls
Number o f
Trout _ _
Samples
Trout _ _
Samples
Trout _ _
Samples
Trout _ _
Samples
1951
1950
No. tim es
No. tim es
recaptured
recaptured
.........-4
5 T otal
2
4
I
3
2
3
I
_43_
13- 19_ IL 3 244
——— ———— P i
39 76 75 18 * 671 ”
212 129 - 6?
-8 4 - 23_ _ 3 _ 26_ io_ 4 JL I . 1 5 3 _
2
12
52 30 Te" 10 ” 6 363
69
168
4
_ _ 1_ — — -J L — — — —— —— • . _ i o _
———— ———
21
6
~12
3
4
407
23_j 23 , 17
67
_____ 2 ______ 196
" lie ” 69 92” 85" 24 ‘1055
392 "201”
4
1949
No. tim es
recaptured
I
-I l-
1F ir s t capture i s added to recapture fo r t o t a ls o f s c a le sam ples.
6
Records o f p la n ts made previous to the study show 23,800 brown trou t
(1 .5 Inches) on June 3 , 1948} 3 ,150 e a ste r n brook tro u t ( 3 Inches) on
June 19, 1947} 28,000 brown tro u t (1 .5 Inches) on June 4 , 1947; and
34 ,3 2 0 brown tr o u t (advanced fr y ) on June 11, 1945.
Although some o f
th ese plan ted f is h may be Included in the w ild tro u t numbers, a l l would
have been in the stream a t le a s t one year b efo re f i r s t capture in 1949.
The four p la n ts o f h a tch ery -ra ised rainbow tr o u t made in F r ic k le y Pear
Creek during the period e f study were as fo llo w s: 2955 fln g e r lln g s
(2 -5 in ch es) on September 3 , 1949; 811 y e a r lin g s (average 6 in ch es)
on May 13, 1950} 3000 fln g e r lln g s (average 3 in ch es) on September 17,
1950; and 997 y e a r lin g s (average 6 in ch es) on May 17, 1951.
A to ta l of
129 s c a le samples were taken from recaptured hatchery f i s h in 1950 and
1951.
Savage Lake (Lincoln. County, Montana) r eceiv ed a p la n t o f 50,000
rainbow tr o u t fr y on March 18, 1949.
The lak e had been p r e v io u sly p o iso n ­
ed on August 23, 1943, and p r a c tic a lly a l l o f the f i s h removed.
Scale
samples were obtained from three o f the p la n ted f is h in 1949, 52 in 1950,
and 14 in 1951.
S cale samples were secured from 63 known-age rainbow tr o u t a t the
U. S . F ish and W ild life S erv ice F ish Hatchery, E nnis, Montana.
These
tr o u t were brood sto c k from f iv e d if f e r e n t year c la s s e s , each o f which
could be id e n t if ie d by a combination o f c lip p ed f i n s .
Water temperature
o f the ponds in which the brood sto c k was h eld did not vary more than
p lu s or minus f iv e degrees from 50 degrees Fahrenheit throughout the y ea r.
7
Methods
In P r lc k le y Pear Greek, most o f the s c a le samples came from trou t
captured w ith an A. C. e l e c t r i c shocker, ( c o lle c t io n p e r io d s. Table 2 ) .
Only 51 samples were secured from tro u t caught by fisherm en,
"shocked"
f i s h were a n e s th e tiz e d in a s o lu tio n o f urethane, and when s u f f i c ie n t ly
calmed, were w eighed, t o t a l len g th measured, and s c a le samples taken.
A fter recovery In h old in g c a g es, f i s h were r e le a se d In the areas from
which th ey were captured.
Wild tr o u t, on f i r s t captu re, were marked
w ith numbered, m etal jaw ta g s .
S ca le samples were taken on a l l w ild
tro u t a t the time o f f i r s t captu re, and on a l l recaptured f i s h from
November, 1949, to October, 1951.
Table 2
C o lle c tio n p eriod s and areas o f s c a le removal
Year
1949
1949
1949
1949
1950
1950
1950
1951
1951
Number
I
2
3
4
5
6
7
8
9
I n c lu s iv e dates
June 22 - July 13
August 11 - 17
September 16 - 23
November 2 4 - 2 7
June 2 2 - 3 0
August 7 - 1 5
September Iti - 25
J u ly 7 - 1 8
September 6 - 1 4
S e c tio n o f d o rsa l f i n below
which s c a le sample was removed
A nterior A nterior Middle
Middle
P o ste r io r P o s te r io r -
le ft
r ig h t
le ft
r ig h t
le ft
r ig h t
S cales were removed from the f i s h In the area between the d orsal
f i n and the la t e r a l l i n e .
To minimize the number o f regenerated s c a le s
taken, t h is area was d iv id ed in to th ree s e c tio n s on each s id e as fo llo w s:
below the a n te r io r o n e -th ir d , below the mid o n e -th ir d , and below the
p o s te r io r o n e -th ir d o f the d o rsa l f i n .
On f i r s t captu re, a l l s c a le
8
samples
were taken on the l e f t s id e o f the f i s h below the a n te r io r o n e -th ir d
o f the d orsal
in , and on recaptured f i s h , a d if fe r e n t s e c t io n was used fo r
each c o lle c t i o n p erio d , (Table 2 ) .
Hatchery tr o u t p lan ted in P r ic k le y Pear Creek were id e n t if ie d by
c lip p in g the ad ip ose and e it h e r the r ig h t or l e f t p e lv ic f i n .
These f i s h
were c o lle c t e d a t the same tim e and in the came manner a s w ild tr o u t.
In Savage Lake, a l l s c a le samples were obtained from f i s h caught by
a n g lin g .
The brood tr o u t from the Ennis Hatchery were secured w ith a dip n e t.
A ll s c a le s taken from 21 o f 63 hatchery f i s h were r eg e n e r a te .
This la rg e
p roportion o f regenerated s c a le s in hatchery brood sto c k may be the r e s u lt
o f handling a t p revious spawning o p e r a tio n s.
S ca les used in t h is stud y were mounted in a gum a rab le medium on g la s s
s lid e s .
S ix good s c a le s were mounted, i f a v a ila b le , fo r each sample.
S ca les were p r o je c ted on a con ven tion al type s c a le machine fo r in te r p r e t­
a tio n , a t which tim e, th e an n u li p o s itio n s and the c i r c u i t counts along the
a n te r io r rad iu s o f the s c a le were marked on heavy paper ta b s .
Any obvious
ir r e g u la r it ie s in s c a le characters were a ls o noted on the ta b s.
Some o f th e s c a le s were photographed in order to f a c i l i t a t e more
minute comparisons o f s c a le ch a r a cter s.
Photographs perm itted sim ultane­
ous view ing o f s c a le s taken a t d if f e r e n t tim es from the same f i s h .
S ca les
were used a s n e g a tiv e s in the photographing process and p ro jected onto
F-4 Kodak Velox s in g le w eigh t paper.
was u sed .
Recommended d evelopin g procedure
A s ta g e micrometer was used to determine m a g n ific a tio n s.
9
S c a le c h a r a c t e r s on " k n o w n -a g e " w i l d t r o u t
A n n u li w e re d e te r m in e d by t h e u s u a l c h a r a c t e r s o f " c u t t i n g o v e r " ,
p a c k in g o f c l r c u l l , a n d I r r e g u l a r i t i e s a s s o c i a t e d w i t h a c h a n g e I n g ro w th
o f th e s c a l e .
I),
Some s c a l e s la c k e d a b a n d o f c l o s e l y s p a c e d c l r c u l l ( F i g .
i n o t h e r s t h e p e r i p h e r a l a r e a w as s o jumbled t h a t I n t e r p r e t a t i o n
w as im p o s s ib l e ( F i g . 2 ) .
I n g e n e r a l , a n n u l i on t h e s c a l e s o f o l d e r
t r o u t w e re l e s s d e f i n i t e b ey o n d t h e t h i r d ;
t h e i r c l o s e p r o x im it y t o o n e
a n o t h e r I n t h e o u t e r r e g i o n o f t h e s c a l e m ade i n t e r p r e t a t i o n d i f f i c u l t .
E r o s i o n o r a b s o r p t i o n o b l i t e r a t e d s c a l e c h a r a c t e r s I n many i n s t a n c e s
(F ig . 3 ) .
A n n u li o n s c a l e s t a k e n i n 1949 a n d 1950 w ere f i r s t d e te r m in e d w i t h ­
o u t r e f e r r i n g t o t h e h i s t o r y o f t h e ta g g e d f i s h .
T hese d e te r m in a tio n s
w e re l a t e r co m p ared t o t h e " k n o w n -ag e " p o r t i o n o f g ro w th a n d w ere fo u n d
to g e n e ra lly a g re e .
A n n u li w e re u s u a l l y c o m p le te a n d s u r r o u n d e d b y fro m o n e t o f o u r
c l r c u l l by l a t e J u n e f o r f i s h fro m P r i c k l e y P e a r C r e e k .
B etw een t h e
l a s t 1949 c o l l e c t i o n p e r i o d (Novem ber 2 4 - 2 7 ) a n d t h e f i r s t 1950 (J u n e
2 2 - 3 0 ) , 7 4 .8 p e r c e n t o f 107 brow n t r o u t , 8 9 .3 p e r c e n t o f 28 rain b o w t r o u t ,
a n d a l l ( 2 ) e a s t e r n b ro o k t r o u t h a d fo rm e d new a n n u l i .
B etw een t h e l a s t 1950 c o l l e c t i o n p e r i o d (S e p te m b e r 1 8 -2 5 ) and t h e
f i r s t 1951 ( J u l y 7 - 1 8 ) , 7 2 .3 p e r c e n t o f 47 brow n t r o u t a n d 7 8 .6 p e r c e n t
o f 14 ra in b o w t r o u t h a d form ed new a n n u l i .
Some t r o u t f a i l e d t o fo rm a n n u l i d u r i n g th e p e r i o d o f a n n u lu s fo rm ­
a t i o n b e tw e e n c a p t u r e i n o n e g ro w in g s e a s o n and r e c a p t u r e I n th e n e x t .
10
T h i s f a i l u r e w as a lm o s t a lw a y s a s s o c i a t e d w i t h l i t t l e
o r no In c re a s e in
b o d y l e n g t h a n d o c c u r r e d , f o r t h e m o st p a r t , i n o l d e r f i s h
o v e r).
(3 y e a rs o r
T o t a l l e n g t h g a i n s o f l e s s t h a n 0 . 8 o f a n I n c h b e tw e e n g ro w in g
s e a s o n s w e re fo u n d i n 69 i n s t a n c e s f o r brow n t r o u t , 15 f o r ra in b o w t r o u t ,
a n d two f o r e a s t e r n b r o o k t r o u t .
I n t h e s e s lo w -g ro w in g f i s h ,
th e e x ­
p e c t e d new a n n u l i w e re l a c k i n g i n 5 9 .4 p e r c e n t o f t h e b ro w n t r o u t ,
3 3 .3
p e r c e n t o f t h e ra in b o w t r o u t , a n d 5 0 .0 p e r c e n t o f t h e e a s t e r n b r o o k t r o u t
( T a b le 3 ) .
S e v e n o f t h e brow n t r o u t a n d t h r e e o f t h e ra in b o w t r o u t i n t h i s
s lo w -g r o w in g g ro u p h a d e i t h e r s o r e m o u th s d u e t o jaw t a g i r r i t a t i o n , o r
d e fo rm e d b a c k s , p r o b a b l y r e s u l t i n g fro m t h e e f f e c t o f e l e c t r i c s h o c k in g .
E i g h t o f t h e s e 10 f i s h f a i l e d t o fo rm a n n u l i d u r in g t h e e x p e c t e d a n n u lu s
f o r m a ti o n p e r i o d s .
I n a l l t r o u t co m b in ed t h e r e w e re 219 g a i n s i n t o t a l
l e n g t h o f m ore t h a n 0 .8 o f a n i n c h b e tw e e n g ro w in g s e a s o n s .
O nly 3 .7
p e r c e n t o f t h e s e f a i l e d t o fo rm new a n n u l i a s e x p e c t e d .
A c o m p a ris o n w as made b e tw e e n t h e g a i n i n t h e num ber o f s c a l e c i r c u l i
a n d t h e i n c r e a s e i n t o t a l body l e n g t h f o r t h e i n t e r v a l s b e tw e e n c o l l e c t i o n
p e r i o d s f o r e a c h a g e c l a s s o f t h e "k n o w n -a g e " w i l d t r o u t .
T h e re was c o n ­
s i d e r a b l e v a r i a t i o n i n t h e s e m e a s u re m e n ts b e tw e e n i n d i v i d u a l f i s h .
A v e r­
a g e s f o r t h e brow n t r o u t a n d t h e ra in b o w t r o u t , h o w e v e r, w e r e som ew hat s im ­
ila r
( T a b le 4 ) , w i t h to o few e a s t e r n b r o o k t r o u t t o j u s t i f y c o m p a ris o n .
I n 58 i n s t a n c e s , t h e c i r c u l i a n d b o d y l e n g t h g a i n s f o r b ro w n t r o u t (4 7 3 )
a n d ra in b o w t r o u t (2 4 9 ) c o v e r e d i d e n t i c a l p e r i o d s .
G a in s i n b o th body
l e n g t h a n d num ber o f c i r c u l i d e c r e a s e d i n f i s h p a s t t h e i r s e c o n d y e a r th e s h a r p e s t d e c re a s e o c c u rrin g a f t e r th e t h i r d y e a r .
C om bined a v e r a g e s
11
o f g a i n s show ed t h a t o n e c I r c u I u s w as fo rm e d f o r a p p r o x i m a t e ly e a c h 0 . 2
o f an in c h g a in in t o t a l body le n g th .
O v e r - a l l brow n t r o u t g a in s w e re
s l i g h t l y b e t t e r t h a n t h o s e o f t h e ra in b o w t r o u t .
The p e r c e n t o f i n c r e a s e i n b o d y l e n g t h w as p l o t t e d a g a i n s t t h e p e r ­
c e n t o f i n c r e a s e i n l e n g t h o f t h e a n t e r i o r s c a l e r a d i u s f o r 196 t r o u t
(1 2 0 c o m p a r is o n s ) .
A t o t a l o f 26 s c a l e r a d i u s c o m p a ris o n s w e re e i t h e r
z e r o o r m in u s v a l u e s , w h i l e o n ly i n f o u r c a s e s d i d f i s h sh o w in g s u c h
v a lu e s f a l l to in c r e a s e i n body le n g th .
To t e s t w h e th e r o r n o t t h e s e
m in u s v a l u e s r e s u l t e d fro m s c a l e s a m p lin g m e th o d s , a n t e r i o r r a d i u s
m e a s u re m e n ts o f 20 s c a l e s fro m e a c h o f t h e s i x s a m p lin g a r e a s w e re made
o n s i x ra in b o w t r o u t a n d f i v e brow n t r o u t (9 -1 6 i n c h e s t o t a l l e n g t h ) .
T h e s e f i s h w e re c o l l e c t e d fro m t h e W est G a l l a t i n R iv e r on November 1 1 , 1 9 5 2 .
D i f f e r e n c e s b e tw e e n t h e l a r g e s t a n d s m a l l e s t m e a su re m e n t w i t h i n an y one
a r e a r a n g e d fro m 2 7 .0 t o 1 1 2 .6 m i l l i m e t e r s
(X 1 4 7 ) .
M eans o f th e 20 a n t e r ­
i o r r a d i u s m e a s u r e m e n ts , h o w e v e r, show ed t h a t s c a l e s i n c r e a s e d i n s i z e fro m
a n t e r i o r t o p o s t e r i o r , a n d t h a t s c a l e s fro m c o m p a ra b le a r e a s on r i g h t a n d
l e f t s i d e s w e re o f s i m i l a r s i z e .
I t w as n o t p o s s i b l e , w i t h t h e s c a l e
s a m p lin g t e c h n i q u e u s e d , t o d e te r m in e t h e e x a c t r e l a t i o n s h i p b e tw e e n body
le n g th and a n t e r i o r s c a l e r a d i u s .
Such i n f o r m a t i o n c o u ld o n l y be o b t a i n e d
fro m s c a l e s t a k e n w i t h g r e a t c a r e fro m v e r y l i m i t e d , o r " k e y " a r e a s .
12
Table 3
Annulua form ation and t o t a l len gth g a in s
Age
Claae
From
Nov. 1949
C o lle c tio n
to
June 1950
c o lle c t io n
Annulus
With W ithout
From
Nov. 1949
C o lle ctio n
to
l a s t 1950
c o lle c t io n
Annulus
Wlthj WlthJ
I out
From
S e p t. 1950
C o lle c tio n
to
July
1951
c o lle c t io n
Annulus
Wlthj WithI out
From
Sept. 1950
C o lle c tio n
to
l a s t 1951
c o lle c t io n
Annulus
Wlthj WithI out
BRttfN TROUT
0
I
II
III
IV
V
T o ta ls
T o ta l len g th
gain s l e s s
than 0 .8 Inch
T o tal len g th
gain s more
than 0 . 8 inch
0
I
II
III
IV
T o ta ls
T o ta l len gth
gain s le a s
than 0 . 8 Inch
T o ta l len gth
gain s more
than 0 .8 inch
I
II
T o ta ls
T o tal len g th
ga in s le s s
than 0 . 8 inch
T o ta l len g th
gain s more
than 0 .8 Inch
4
40
17
16
6
I
84
I
0
I
10
9
2
23
12
61
26
28
8
I
136
0
0
0
15
13
3
31
2
4
21
4
3
0
34
6'
0
0
5
8
0
13
4
7
28
6
6
0
51
6
0
0
5
9
I
15
7
21
24
29
4
10
4
12
77
2
112
2
30
5
47
3
I
12
11
I
0
25
0
I
I
0
I
3
1
21
17
2
0
41
0
I
1
0
2
4
I
0
11
d
0
2
I
0
3
I
16
3
I
0
21
0
0
2
I
0
3
9
3
9
4
I
I
I
I
16
0
52
I
10
2
20
2
I
I
2
0
0
0
I
I
2
0
I
I
0
0
0
0
0
0
0
0
0
0
0
0
I
I
I
I
I
0
•1
13
Table 4
T otal len gth ga in s and c l r c u l l g a in s between c o lle c t io n periods
0
Brown Trout
C lr c u li
No.
F ish Gain
358
1 -6
406
1 -7
447
2 -5
315
2
2 -6
363
2
2 -7
404
I
3 -5
278
I
3 -6
326
2
3 -7
367
I
212
2
4 -6
260
2
4 -7
301
3
5 -6
48
5 -7
89
i
CO
Ul
I
1 -5
m
C o lle c tio n
period*
Av.
No.
Days
CO
41
i
6 -7
O'
444
2
( 2- 2 )
10
(6-14)
6
0.4"
(0 . 0- 0 . 8 )
!.O u
( 0 .7 - 2 .5 )
1 . 1"
3
0.5"
10
(8- 11)
10
1. 8 "
( I . 5 -2 .0 )
2 . 2U
8
1. 6"
2
( 1- 2 )
10
(9-11)
12
(10-14)
-0 . 6 "
( 0 .5 - 0 .7 )
2 . 1"
( 2 . 0- 2 . 2)
2.5"
( 2 .0 - 3 .0 )
12
2 . 6"
0
0.4"
9
2 .4 U
I
I
331
I
oo
•
I
VD
364
2
VO
59
I
OeOir
I
305
I
3
I
11
1T able 2
Rainbow Trout
Length
C ir c u li
Gain
Gain
-
396
6 -9
No.
F ish
384
5 -9
CO
Length
Gain
2.9"
-
15
(13-17)
-2 . 6»
( 2 . 6- 2 . 6 )
9
I
2 . 0"
14
Table 4
(continued)
I
Bi own T rou t.
1 -5
358
13
1 -6
406
8
1 -7
447
9
2 -5
315
21
2 -6
363
20
2 -7
404
12
3 -5
278
3
326
3
3 -7
367
2
4 -5
212
3
4 -6
260
2
4 -7
301
I
5 -6
48
b
5 -7
89
8
5 -8
384
I
vO
No.
F ish
«
to
C o lle c tio n
period
Av.
No.
Days
C ir c u ll
Gain
10
( 6- 12)
15
(6-17)
15
( 11- 20 )
4
(2 -9 )
8
(4-16)
10
(5-19)
3
( 1- 6 )
6
(5 -7 )
10
(6-13)
4
(2 -5 )
7
(3-10)
5
Length
Gain
2 . 0"
( I . 4 -3 .0 )
2.4"
( I . 9 -3 .0 )
3.1"
( 2 .3 - 3 .8 )
1.4"
( 0 . 6- 2 .5 )
2 . 1”
( I . 2- 2 .7 )
2.4"
( I . 3 -3 .2 )
0.7"
(0 .4 - 0 .8 )
1.5"
( 1 . 0- 2 . I)
3 .0
( 2 .7 - 3 .3 )
0 .8"
( 0 .7 - 0 .9 )
1 . 2"
( 0 .9 - 1 .5 )
1 . 1"
6
(4 -8 )
9
(4-15)
15
1 . 1"
( 1. 0- 1 . 2 )
1 . 6"
( I . 1- 2 . 0 )
2 . 8"
21
3.6"
I
6 -7
41
30
6 -8
331
2
6 -9
396
4
305
4
7 -9
364
4
2
(0- 8 )
11
( 11- 11)
14
(8 - 20)
9
(6-15)
10
(4-13)
8 -9
59
8
(1 -9 )
•
444
os
5 -9
0.4"
(0 . 1- 1 . I)
1.9"
( 1 . 8- 1 .9 )
3.1"
( 2 .6 - 4 .0 )
1.5"
( I . 1- 2 . 0 )
2 . 2"
( 1. 8- 2 .7 )
1 .1
(0 .4 -1 .8 )
Rainbow Tro lit
No.
C ir c u it
Length
F ish Gain
Gain
8
2 . 0"
2
( 1 . 8- 2 . 2 )
( 6- 10)
10
2.8"
( 2 .4 - 3 .4 )
3
(8- 11)
13
3.3"
2
( 3 .0 - 3 .5 )
(13-13)
2
0.9"
(0 -3 )
(0 .7 - 1 .2 )
3
8
2 . 0"
3
( I . 5 -2 .3 )
(7 -9 )
2 . 2"
10
4
( I . 3 -3 .0 )
(6 -1 5 )
I
1. 1"
( 1- 2 )
( 0 .4 - 1 .0 )
3
2.5"
9
(4 -1 6 )
( 1 . 5 -3 .0 )
3
2 . 2"
8
( I . 6- 2 .9 )
3
(5 -1 1 )
0.7"
3
( 0 .3 - 1 .0 )
(1 -5 )
5
1.5"
9
(5 -1 5 )
3
( I . 3 -1 .8 )
1. 6"
5
(0
-1
4
)
3
( 1. 0- 2 .3 )
6
1. 1"
(
0
.4
- 1 .7 )
(4 -9 )
9
8
1.7"
( 5- 12)
( 0 .4 - 2 .3 )
7
13
2.7"
(12-14)
2
(2 .4 - 2 .9 )
3.4"
16
I
0 . 6"
2
(0
.
0- 1. 2 )
(0- 6 )
46
2 . 0"
9
(
I
.
7 -2 .3 )
6
(5 -1 1 )
14
2. 8"
( I . 4 -4 .4 )
(5 -2 5 )
8
1. 2"
7
( I . 0 -1 .3 )
4
( 2- 10)
13
1.9"
( I . 0- 2 .4 )
( 9- 22 )
5
I i 2"
6
12
(0 . 6- 1. 8 )
1(3-9)
15
Table 4 (continued)
I - 5
358
1 -6
406
1 -7
447
2 - 5
315
363
•
C o lle c tio n
p e rio d
W
11
A v.
No.
Daye
3 - 5
278
3 - 6
326
3 - 7
367
4 - 5
212
4 - 6
260
4 - 7
301
5 -6
48
26
89
19
5 -8
384
8
5 - 9
444
5
6 -7
41
31
6 - 8
331
13
6 - 9
396
9
305
11
364
11
59
5
CD
404
I
2 -7
I
Brown T r o u t
N o.
C irc u li
F is h
G ain
7
14
(1 -1 2 )
8
(5 -1 2 )
8
6
( 0 -1 1 )
8
6
(2 -9 )
2
9
I
8
(4 -1 1 )
2
4
(3 -4 )
2
8
(7 -9 )
2
8
2
(2 -1 3 )
VO
I
CO
7 -9
4
(1 -9 )
5
(1 -8 )
14
(1 0 -2 1 )
7
(1 0 -1 3 )
2
(0 -6 )
8
( 3 -1 4 )
7
(1 -1 6 )
7
(3 -1 3 )
6
(0 -9 )
3
(1 -6 )
L e n g th
G a in
1 .7 "
( 0 .7 - 2 .5 )
1 .3 "
( 6 .6 -2 .2 )
1 .7 "
( 0 .1 -2 .7 )
1 .2 "
( I . 0 - 1 .3 )
1 .9 "
No.
F is h
4
5
3
5
R ainbow T ro u t
C irc u li
G a in
S
(4 -1 1 )
14
(8 -1 8 )
15
(1 2 -1 8 )
2
(0 -5 )
6
L e n g th
G a in
1 .7 "
( 0 .9 -2 .4 )
2 .5 "
( I .8 - 3 .3 )
2 .3 "
( 2 .0 -5 .6 )
0 .6 "
( 0 .0 -1 .8 )
2 .5 "
I
2 .9 "
( 2 .1 -3 .6 )
1 .0 "
( 0 .7 -1 .2 )
1 .6 "
( 1 .4 -1 .7 )
2 .3 "
( 1 .9 - 2 .7 )
0 .5 "
( 0 .1 -1 .I)
0 .9 "
( 0 .4 - 1 .3)
2 .3 "
( I . 1 - 3 .4 )
2 .4 "
( I . 2 - 3 .3 )
0 .4 "
( 0 .1 - 0 .8 )
1 .9 "
( I . 5 - 2 .4 )
1 .9 ”
( 0 .6 - 3 .0 )
1 .4 "
( 1 .0 - 1 .8 )
1 .6 "
( 0 .5 - 2 .3 )
0 .5 "
( 0 .3 - 0 .8 )
3
1: 7 * -
I
2
2
(1 -3 )
0 .0 "
( 0 .0 - 0 .0 )
2
4
(2 -5 )
0 .7 "
( 0 .5 - 0 .9 )
4
(0 -8 )
6
(2 -9 )
9
(5 -1 5 )
12
(1 1 -1 2 )
I
(0 -4 )
4
(1 -9 )
5
1 .1 "
( 0 .5 - 1 .2 )
1 .0 "
( 0 .1 -1 .6 )
1 .9 "
( I . 6 - 2 .4 )
2 .6 "
( 2 .5 -2 .7 )
0 .2 "
( 0 .1 -0 .5 )
0 .5 "
( 0 .2 - 0 .8 )
0 .5 ”
I
(0 -2 )
7
(5 -9 )
4
(0 -7 )
0 .3 ”
( 0 .3 -0 .4 )
1 .1 ”
( 0 .9 -1 .2 )
0 .9 ”
( 0 .2 -1 .6 )
11
8
4
2
16
3
I
3
2
10
16
Table 4 (continued)
.............. m ~
1 -5
358
1 -6
406
1 -7
447
2 -5
315
2 - 6
363
2 - 7
404
3 - 5
278
3 - 6
326
CO
567
I
C o lle c tio n
p e rio d
A v.
H o.
Dcya
B rcrm T r o u t
C irc u it
H o.
F is k
G a in
3
22
(0 -7 )
2
12
(0 -5 )
4
11
(1 -9 )
3
2
(1 -5 )
6
I
3
2
(1 -5 )
4
I
5
I
2
2
(2 -2 )
4 - 6
260
4 -7
301
5 - 6
48
8
5 - 7
89
10
5 - 8
384
6
5 -9
444
4
6 -7
41
12
6 - 8
331
6
6 -9
396
6
r***,
305
3
364
4
59
7
I
212
CO
4 - 5
7 -9
I
Ox
OO
2
(0 -3 )
2
(0 -5 )
4
(0 -9 )
6
(3 -1 1 )
2
(0 -3 )
4
(0 -6 )
5
(1 -9 )
3
(2 -4 )
4
(0 -7 )
2
(0 -9 )
' ................... — ... R ainbow T r o u t
L isngth
Ho.
C irc u it
7C n g tb
G a in
F is h
G a in
G a in
0 .8 "
3
0 .0 "
I
( 0 .1 - 1 .5 )
1 .4 "
6
0 .8 "
( 0 .0 -1 .9 )
I
1 .1 "
( 0 .1 -1 .7 )
0 .8 "
( 0 .5 -1 ,0 )
1.2'+
0 .9 "
( 0 .5 -1 .2 )
0 .5 "
0 .9 "
0 .3 "
( 0 .1 - 0 .4 )
I
0 .2 '*
I ( 0 .0 - 0 .5 )
0 .6 "
( 0 .1 * 2 .0 )
0 .9 "
( 0 .4 -2 .I)
1 .5 "
( 0 .3 -2 .8 )
0 .2 "
( 0 .0 - 0 .5 )
0 .6 "
( 0 .2 - 1 .6 )
1 .6 «
( 0 .7 -2 .9 )
I
0 .6 "
I ( 0 .4 - 1 .I)
I
* 1 .5 "
I (0.6-2.7)
0 .5 "
I ( 0 .1 -1 .3 )
2
3
4
(2 -6 )
4
(4 -3 )
I
0 .1 "
( 0 .0 - 0 .3 )
0 .4 "
( 0 .0 -0 .8 )
0 .4 "
I
-2
0 .0 "
I
6
2
2
(-2 -5 )
I
(-2 -3 )
-4
0 .3 "
( 0 .1 -0 .6 )
-0 .6 «
( 0 .6 - 0 .6 )
0 .6 "
I
-2
0 .4 "
-4
0 .4 "
I
I
3
I
(-2 -5 )
0 .4 "
( 0 .0 - 0 .9 )
T a b le 4
A v.
C o lle c tio n
period
No.
Days
Brown Trout
C lr c u ll
(c o n tin u e d )
Rainbow Trout
C lr c u ll
F ish
Gaia
len g th
Brown Trout
C lr c u ll
L e n g th
G a in
18
E f f e c t s o f s h o c k in g , h a n d l i n g , a n d t a g g i n g o f t r o u t
on t h e i r s c a l e c h a r a c t e r s
A c o m p a ris o n b e tw e e n a v e r a g e t o t a l l e n g t h s a t t h e tim e o f c o l l e c t i o n
w as made b e tw e e n ta g g e d w i l d t r o u t w h ic h h a d b e e n r e c a p t u r e d fro m o n e to
f i v e tim e s a n d w i l d t r o u t frtn a t h e sam e a r e a c a p t u r e d o n l y o n c e (T a b le 5 ) .
T a g g e d brow n t r o u t i n t h e i r t h i r d y e a r o f l i f e a v e r a g e d 5 . 6 p e r c e n t s m a l l e r
t h a n b ro w n t r o u t o f t h e sam e a g e c l a s s c a p t u r e d o n ly o n c e .
In th e ir fo u rth
y e a r , t h e t a g g e d brow n t r o u t w e re 9 . 0 p e r c e n t s m a l l e r , a n d i n t h e i r f i f t h
y e a r , 7 .0 p e r c e n t s m a l l e r .
T he s lo w e r g ro w th r a t e o f t h e o l d e r ta g g e d b ro w n
t r o u t w as c h a r a c t e r i s e d b y t h e c l o s e p r o x i m i t y o f a n n u l i o n t h e o u t e r e d g e s
o f t h e s c a l e s , a n d t h e f a i l u r e , i n some i n s t a n c e s , t o f o r a new a n n u l i .
R ainbow t r o u t w e re a p p a r e n t l y l e s s a f f e c t e d b y t h e s h o c k in g , h a n d l i n g ,
and ta g g in g .
T o t a l l e n g t h s w i t h i n y e a r c l a s s e s f o r t h e t a g g e d ra in b o w
t r o u t w e re v e r y s i m i l a r t o t h o s e o f t h e ra in b o w t r o u t c a p t u r e d o n ly o n c e .
" c h e c k - m a rk s " w h ic h may h a v e b e e n c a u s e d b y s h o c k in g , h a n d l i n g , a n d
t a g g i n g w e re p r e s e n t o n som e s c a l e s ( F i g . 4 , 5 , 6 , 7 ) , h o w e v e r, m o st o f
t h e s c a l e m ark s d i d n o t o c c u r w i t h a n y r e g u l a r i t y a n d w e re p e c u l i a r t o
th e in d iv id u a l f i s h r a t h e r th a n to g ro u p s.
S c a le c h a r a c t e r s o f h a t c h e r y - r a i s e d ra in b o w t r o u t
p l a n t e d i n P r i c k l c y P e a r C re e k
One g r o u p o f ra in b o w t r o u t f i n g e r l i n g s w e re f i n c l i p p e d S e p tem b e r 8 ,
1949.
Of t h i s g r o u p , 2955 w e re p l a n t e d i n P r i c k l e y P e a r C re e k a n d 100
w e re r e t a i n e d a t t h e h a t c h e r y t o d e te r m in e t h e e x t e n t o f f i n r e g e n e r a t i o n
a s p a r t o f a n o th e r s tu d y .
S c a le s t a k e n fro m l i a t c h e r y - h e I d f i s h May 3 , 1 9 5 0 ,
19
e x h i b i t e d a "ch eck -m ark * 1 ( F i g . 8 ) v e r y s i m i l a r I n p o s i t i o n t o t h e a n n u lu s
( F i g . 9 ) o n s c a l e s t a k e n fro m t h e p l a n t e d f i s h on A u g u st 1 0 , 1 9 5 0 .
S c a le s
t a k e n fro m t h e p l a n t e d t r o u t on J u l y 9 , 1 9 5 1 , h ad two a n n u l i w i t h g ro w th
beyond ( F ig . 1 0 ) .
S c a l e s fro m t r o u t o f t h i s g ro u p w h ic h h a d b e e n p l a n t e d
i n P r l c k l e y P e a r C re e k h a d no d i s c e r n i b l e d i f f e r e n c e s fro m s c a l e s o f w i l d
t r o u t o f c o m p a ra b le a g e a n d s i z e .
T a b le 5
A v e ra g e l e n g t h s o f P r l c k l e y P e a r t r o u t a t tim e o f c a p t u r e
BROWN TROUT
C o lle c tio n
p e rio d 1
I
2
3
4
5
6
7
8
9
I
2
3
4
5
6
7
8
9
O
R ecap
tu re d
3 .0
3 .9
4 .2
3 .8
3 .9
O
W ild ‘
2 .9
3 .3
4 .0
4 .2
2 .1
3 .7
3 .5
4 .1
4 .5
4 .9
4 .0
1T a b le 2
2B is h o p (1 9 5 3 )
2 ,7
3 .5
3 .8
3 .6
2 .9
R ecap
tu re d
5 .5
6 .4
6 .8
6 .3
4 .9
5 .8
6 .3
5 .0
6 .0
RAINBCT5 .2
6 .3
6 .7
6 .6
4 .7
5 .8
6 .4
5 .2
6 .3
W ild
5 .6
6 .2
6 .6
7 .1
4 .9
5 .7
6 .4
5 .0
6 .2
TROUT
5 .4
6 .1
6 .3
6 .9
4 .6
5 .8
6 .2
4 .8
6 .6
TI
R ecap
t u r e d W ild
8 .3
8 .3
8 .8
8 .0
9 .3
1 0 .1
1 0 .4
7 .8
7 .7
8 .5
9 .7
8 .8
1 1 .1
7 .8
8 .0
8 .5
9 .2
8 .4
9 .6
9 .5
9 .3
7 .5
8 .1
8 .4
7 .6
8 .3
8 .1
9 .2
8 .6
9 .8
7 .1
8 .9
9 .0
7 .7
9 .6
__ I I I ____
[V
R ecap
R ecap
t u r e d J i l d t u r e d v i ld
1 1 .0 1 1 .4 1 3 .8
1 4 .0
1 1 .9 1 2 .3 1 3 .9 1 5 .8
1 2 .2 1 5 .5
1 3 .2
1 0 .9 1 2 .3
1 5 .2
1 0 .8 1 2 .2 1 3 .0 1 3 .8
1 0 .9 1 2 .3 1 2 .9 1 6 .1
1 1 .0 1 1 .8 1 2 .8 1 3 .8
1 0 .5 1 1 .7 1 3 .5 1 3 .3
1 0 .5 p.2.5 1 3 .2 1 3 .6
1 0 .0 1 0 .9
L 1.0
L I .9
1 2 .8
1 0 . 1 8 .5
1 0 .9 1 0 .4
1 1 .1 L 1.0
1 0 .1 9 .7
1 0 .0 9 .0
1 2 .3
1 1 .2
1 1 .6
1 1 .8
9 .8
1 2 .8
1 2 .5
1 0 .4
1 5 .4
20
Y earling rainbow tro u t which averaged 6 inches in t o t a l length were
p lan ted on May 13, 1950.
S ca les taken from th ese f i s h on June 17, 1950,
had c lo s e ly packed c i r c u i t near the ou ter edge and e x h ib ite d two to four
"check-marks" (F ig . 11, 1 2 ).
S ca les from most w ild tr o u t c o lle c te d a t t h is
time had new a n n u li and se v e r a l w id ely spaced c ir c u i t beyond.
M iller (1952)
found th a t p lan ted tr o u t did not begin e a tin g fo r about 40 d a y s, and B hatia
(1932) produced s o - c a lle d "annual zones" on th e s c a le s o f tr o u t by a lte r in g
the food su p p lie s o f the f i s h .
These fin d in g s may e x p la in the slow growth
in d ic a te d on the s c a le s o f p lan ted y e a r lin g f i s h .
Y oun g-of-the-year rainbow tro u t which averaged 3 in ch es in t o t a l
len g th were p lan ted in P r lc k le y Pear Creek on September 17, 1950.
On
Novmber 24, 1950, s c a le s from th ese f i s h had c lo s e ly spaced c ir c u i t near
the edges (F ig . 1 3 ), but did not d if f e r g r e a tly from s c a le s o f w ild tro u t
o f approxim ately the same s i z e c o lle c t e d a t the same time (F ig . 1 4 ).
S c a le s taken September 11, 1951, from tr o u t o f th is p la n t had one annulus
w ith average growth beyond.
S c a le s from y e a r lin g rainbow tr o u t p la n ted May 17, 1951, had one to
fou r "check-marks" (F ig . 15, 16) when c o lle c t e d on J u ly 17, 1951.
marks lacked most c h a r a c t e r is tic s o f a n n u li.
These
As w ith y e a r lin g trou t p la n t­
ed in 1950, c ir c u i t were more c lo s e ly packed on the ou ter edges o f th e ir
s c a le s .
S ca le ch aracters o f rainbow tr o u t plan ted in Savage Lake
Rainbow tr o u t fr y were p lan ted in Savage Lake on March 18, 1949.
These f i s h were over 8 in ch es in t o t a l le n g th by August 26, 1949, when
21
s c a le s were tak en .
H ila rather e x c e p tio n a l in crea se in body length
was r e f le c t e d l a the s c a le s which had w id ely spaced c ir c u i t w ith alm ost
no ir r e g u la r it ie s (F ig . 1 7 ).
By June 25, 1950, th ese tr o u t ranged from
9 .3 to 1 1 .0 in ch es in t o t a l le n g th .
S c a le s taken a t t h is tim e e x h ib ited
one annulus and new growth beyond (F ig . 1 8 ).
S ca les were taken again on
August I , 1950, and the o n ly change noted was a d d itio n a l growth beyond
th e ann ulu s.
The l a s t s c a le samples stu d ie d from th e Savage Lake ra in ­
bow tr o u t were taken May 7 , 1951.
The second annulus had n o t formed a t
t h is tim e (F ig . 1 9 ).
S ca le ch aracters o f the Ennis Hatchery rainbow tro u t
"Annuli” on th e s c a le s o f Ennis Hatchery rainbow tr o u t brood sto ck
d id not conform to th e known age o f th e f i s h , nor did they always appear
i n s im ila r p o s itio n s on the s c a le s o f tr o u t o f the same a g e .
S cales from
tr o u t hatched in 1948 had from two to f i v e "annuli" (F ig . 20, 21, 22,
2 3 ).
S ca les from tr o u t hatched in 1947 were eq u a lly as v a ried in "annuli"
numbers (F ig . 2 4, 25, 26, 2 7 ), and could o n ly be d if f e r e n t ia t e d from the
o th er tr o u t by th e f i n - c l i p .
Sin ce tem peratures o f th e ponds in which
the brood sto c k were h eld remained f a i r l y constant throughout the year,
the "annuli" probably r e s u lte d from fe e d in g p r a c tic e s and handling o f the
f i s h during spawning o p e r a tio n s.
Acknowledgements
The a s s is ta n c e o f Dr. C. J . D. Brown, who d ir e c te d t h is study and
a s s is t e d in p rep aration o f the m anuscript, i s g r a te fu lly acknowledged.
22
The Montana F ish and Game Department a s s is t e d f in a n c ia lly in f i e l d and
laboratory work and perm itted the u se o f th e ir s c a le c o lle c t i o n and lab or­
a to r y equipment*
S c a le s taken during th e 1951 p o rtio n o f t h is study were
in clu d ed under D in gell-Joh n son p r o je c t F -5-R -1.
Thanks are extended to James Dnmenond o f th e Montana S ta te C ollege
Wool Laboratory fo r the u se o f m icrop ro jectio n and photographic f a c i l i t i e s .
Summary
1.
S ca le samples taken and stu d ied during the p eriod from June,
1949 to O ctober, 1951, inclu ded 1055 from tagged w ild tr o u t and 129 from
p la n ted tr o u t in P r ic k le y Pear Creek, Montana; 52 from tr o u t p lan ted in
Savage Lake, Montana; and 42 from rainbow tr o u t brood s to c k a t the U. S.
F ish and W ild life S e r v ice F ish Hatchery, E n n is, Montana.
2.
S c a le s from "known-age" brown tr o u t , rainbow t r o u t , and ea stern
brook tr o u t were s tu d ie d .
3.
S c a le s from tr o u t overthree years o ld were more d i f f i c u l t to
in te r p r e t than th ose from younger f i s h .
Annuli were in c lo s e r proxim ity
on the s c a le s o f the o ld e r f i s h and, in many in s ta n c e s , e r o sio n or ab­
so r p tio n o b lite r a te d s c a le c h a r a cter s.
4.
By the la t t e r p art o f June, 1950, 74 .8 p ercen t o f th e brown tr o u t,
8 9 .3 p ercen t o f th e rainbow tr o u t, and a l l ( 2 ) e a ste r n brook trou t had
formed new a n n u li.
In 1951, 7 2 .3 p ercen t o f the brown tr o u t and 7 8 .6 per­
cen t o f th e rainbow tr o u t had formed new a n n u li by th e second week in J u ly .
23
5.
The f a ilu r e o f tr o u t, in some in s ta n c e s , to form new an n u li during
the period o f annulus form ation was alm ost always a s s o c ia te d w ith l i t t l e
or no In crease in body le n g th .
6.
Tagged brown tr o u t in th e ir th ir d , fo u rth , and f i f t h years were
5 .6 , 9 .0 , and 7 .0 p ercen t sm aller r e s p e c t iv e ly , than brown tro u t o f the
same age c la s s e s captured o n ly once.
W ithin year c l a s s e s , t o t a l len gth s
o f tagged rainbow tro u t were very s im ila r to th ose o f rainbow tro u t cap­
tured o n ly once.
7.
S ca le marks which may have been caused by sh ock in g, handling,
and taggin g were p resen t on some s c a le s , bu t did not occur w ith any u n i­
form ity or r e g u la r ity .
8.
In in d iv id u a l f i s h , there was co n sid era b le v a r ia tio n between the
g a in in number o f s c a le c ir c u i t and th e in c r ea se in t o t a l body len gth fo r
th e in te r v a ls between c o lle c t io n p e r io d s .
tr o u t and rainbow tr o u t were s im ila r .
Averages o f g a in s fo r the brown
Combined averages showed one c ir -
cuIus formed fo r approxim ately each 0 . 2 o f an inch g a in in t o t a l body
le n g th .
9.
S ca le s iz e s (a n te r io r r a d iu s) w ith in the s i x sampling areas used
showed d iffe r e n c e s o f 2 7 .0 to 112.6 m illim e te r s (X 147) w ith in an a r ea .
Averages o f rad iu s measurements w ith in a l l areas showed an in crea se in
s c a le s i z e from a n te r io r to p o s te r io r .
S c a le s from comparable areas on
r ig h t and l e f t s id e s were o f sim ila r s i z e .
10.
S c a le s from marked rainbow tr o u t fiu g e r lin g s p la n ted in P r ic k le y
Pear Creek in 1949 and 1950 were l i t t l e d if f e r e n t from s c a le s o f w ild f i s h
24
o f comparable age and s i z e .
S cales from h a tch ery -ra ised y e a r lin g rainbow
tr o u t p lan ted in P r ic k le y Pear Creek in 1950 and 1951 had from two to
four "check-marks11, and c lo s e ly spaced c ir c u i t on the o u ter edges o f the
s c a le s in d ic a te d slow er growth fo llo w in g p la n tin g .
11.
S cale ch aracters on rainbow tr o u t plan ted a s fr y in Savage Lake,
Montana, conformed to the known age o f the f i s h .
12.
"Annuli" v a ried con sid erab ly in both number and p o s itio n on
s c a le s o f rainbow tro u t brood sto c k from the Ennis H atchery.
Ages o f the
tr o u t, known from the f i n c l i p s , did not conform to the "annuli" on the
s c a le s .
25
L ite r a tu r e C ite d
A p p le g a te , V ern o n C .
1 9 4 7 . G row th o f some la k e t r o u t , C r i s t i v o m e r n . namaycush.
o f known a g e i n i n l a n d M ic h ig a n l a k e s . "~C opeia,
1947, S o . 4 , D ec. 3 0, p p . 2 3 7 -2 4 1 .
B h a tia , D.
1932.
F a c t o r s in v o lv e d i n t h e p r o d u c t i o n o f a n n u a l z o n e s
o n t h e s c a l e s o f t h e ra in b o w t r o u t (S e Imo i r i d e u s ) .
J o u r . E x p . B i o l . , V o l. 9 ( 1 9 3 2 ) , p p . 6 - 1 1 .
B is h o p , C l i n t o n G.
1 9 5 3 . A ge, g r o w th , a n d c o n d i t i o n o f t r o u t i n P r i c k l e y P e a r
C r e e k , M o n ta n a . U n p u b lis h e d t h e s i s , M ontana S t a t e C o l l e g e .
B row n, C. J . D.
1 9 4 3 . Age a n d g ro w th o f M ontana g r a y l i n g .
V o l . 7 , N o. 4 , p p . 3 5 3 - 3 6 4 .
J o u r . W i l d l . M g t.,
C o o p e r, E dw in L .
1951. V a lid a tio n o f th e u se o f s c a le s o f b ro o k t r o u t ,
S a lv e n lin u s f o n t i n a l i s . f o r ag e d e te rm in a tio n .
C o p e ia , 1 9 5 1 , N o. 2 , J u n e 3 , p p . 1 4 1 -1 4 8 .
M i l l e r , R ic h a r d B .
1952. S u rv iv a l o f h a tc h e r y - r e a r e d c u tt h r o a t t r o u t in a n
A l b e r t a s t r e a m . T r a n s . Am. F i s h . S o c ., V o l. 81
(1 9 5 1 ), p p . 3 5 -4 2 .
S t e f a n i c h , F r a n k A.
1 9 5 2 . The p o p u l a t i o n a n d m ovem ent o f f i s h i n P r i c k l e y
P e a r C r e e k , M o n ta n a . T r a n s . Am. F i s h . S o c . , V o l.
81 ( 1 9 5 1 ) , p p . 2 6 0 -2 7 4 .
Van O ost e n , J o h n
1 9 2 3 . A s t u d y o f t h e s c a l e s o f w h i t e f i s h e s o f known a g e s .
Z o o lo g ic a , V o l. 2 , N o. 1 7 , p p . 3 8 0 -4 1 2 .
1941.
A sym posium o n h y d r o b io l o g y .
P r e s s , p p . 1 9 6 -2 0 5 .
U n i v e r s i t y o f W is c o n s in
26
E xplanation o f Figures
F i g . I - B rm m t r o u t s c a l e l a c k i n g a b a n d o f c l o s e l y s p a c e d c i r c u i t .
F i g . 2 - Brown t r o u t s c a l e w i t h a ju m b le d p e r i p h e r a l a r e a .
F i g . 3 - Brown t r o u t s c a l e sh o w in g o b l i t e r a t i o n o f s c a l e c h a r a c t e r s by
e ro s io n o r a b s o rp tio n .
F i g . 4 , 5 , 6 , 7 - A s e r i e s o f s c a l e s fro m a brow n t r o u t sh o w in g a
" c h e c k -m a rk " (CM) w h ic h may h a v e b e e n c a u s e d b y s h o c k in g ,
h a n d lin g , and ta g g in g .
F i g . 8 - S c a le fro m a h a t c h e r y - h e l d ra in b o w t r o u t sh o w in g a " c h e c k ­
m ark " (CM).
F i g . 9 - A n n u lu s (A) o n t h e s c a l e o f a ra in b o w t r o u t p l a n t e d i n P r i c k l e y
P e a r C re e k a s a f i n g e r l i n g .
28
Explanation of Figures
F ig . 10 - S cale from rainbow tr o u t p lan ted a s a fin g e r lin g in 1949 show­
ing two a n n u li in 1951.
F ig . 11, 12 - S c a le s from p lan ted y e a r lin g rainbow tro u t showing two to
four "check-marks".
F ig . 15 - S cale from p la n ted rainbow tro u t fln g e r lin g showing more c lo s e ly
spaced c ir c u i t on the outer edge o f the s c a le .
F ig . 14 - S cale from a w ild rainbow tr o u t £ln g e r lin g o f approxim ately the
same e l s e as th e p lan ted tr o u t in F ig . 13.
F ig . 15, 16 - "Check-marks" on the s c a le s o f rainbow tro u t p la n ted as
y e a r lin g s in May, 1951.
F ig . 17 - S ca le from f a s t growing rainbow tr o u t planted as fr y in Savage
Lake.
Approximately s ix months growth is shown on the s c a le .
F ig . 18 - S cale showing one annulus on rainbow tro u t plan ted a s fr y in
Savage Lake.
29
l3 ^
i t
30
E xplanation o f Figures
F i g . 19 - S c a le fro m ra in b c w t r o u t p l a n t e d a s f r y i n S a v a g e Lake i n 1949s e c o n d a n n u lu s h a s n o t y e t fo rm e d i n May o f 1951.
wi g . 2 0 , 2 1 , 2 2 , 23 - S c a le s fro m E n n is H a tc h e r y ra in b o w t r o u t b ro o d s t o c k
(1943 h a t c h ) sh o w in g v a r y i n g n u m b ers o f " a n n u l i ” .
F i g . 2 4 , 2 5 , 2 6 , 27 - S c a le s fro m E n n ia H a tc lte r y ra in b o w t r o u t b ro o d s t o c k
(1947 h a tc h ) w i t h v a r y i n g " a n n u l i "
numbers.
row AO!
31
10551'?.
M ONTANA S T A T E U N IV E R SIT Y L IB R A R IE S
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cop. 4
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