Document ID: EPA-HQ-OW-2003-0068-0032
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-09-22T04:00Z

38
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
What
are
the
conclusions
for
incubation
requirements?

Spawning
signals
the
beginning
of
the
life­
cycle
stage
(
egg
deposition
and
initial
egg
incubation)
that
is
most
sensitive
to
warm
waters.
Critical
spawning
temperatures
for
a
variety
of
salmonids
are
summarized
in
Table
5.
Because
the
spawning
period,
egg
fertilization,
and
initial
incubation
are
sensitive
life
stages
dependent
on
thermal
regimes,
special
consideration
must
be
given
to
ensure
that
criteria
to
protect
incubation
are
applied
at
the
proper
time
of
year.

Table
5.
Upper
optimal
temperature
regimes
based
on
constant
or
acclimation
temperatures
necessary
to
achieve
full
spawning
protection
of
the
nine
key
cold­
water
fish
species
indigenous
to
the
Pacific
Northwest
Fish
species
Critical
spawn
temperatures
Upper
optimal
temperature
range
°
F
(
°
C)
Single
daily
maximum
temperature
°
F
(
°
C)

Chinook
48.2­
50
(
9­
10)
56.3­
58.1
(
13.5­
14.5)

Pink
50­
53.6
(
10­
12)

Chum
46.4­
50
(
8­
10)

Char
35.6­
42.8
(
2­
6)
42.8
(
6)

Sockeye
46.4­
50
(
8­
10)

Coho
44.6­
50
(
7­
10)

Cutthroat
44.6­
50
(
7­
10)

Rainbow
44.6­
50
(
7­
10)

Steelhead
51.8­
53.6
(
11­
12)

Growth
For
growth,
what
are
the
demands
for
energy
and
how
is
the
balance
determined
by
temperature?

In
terms
of
energy
budgets,
fish
production
energy
(
P)
equals
the
sum
of
growth
(
G),
reproduction
(
Rp),
shed
scales
(
Ex),
and
secretions
(
S),
as
shown
in
the
following
equation:

P
=
G
+
Rp
+
Ex
+
S.

Energy
assimilated
from
food
equals
the
difference
between
energy
ingested
and
defecated,
or
A
=
I
!
F.

Energy
assimilated
is
distributed
into
production
(
P),
respiration
(
R),
and
excretion
(
U),
as
39
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
follows:

A
=
P
+
R
+
U.

The
symbols
used
above
follow
terminology
of
Ricker
(
1968)
and
Odum
(
1968).

Energy
is
needed
to
maintain
the
basic
metabolic
rate
and
is
fundamental
to
sustain
life.
In
addition,
some
energy
must
be
diverted
to
activity
(
swimming)
to
perform
the
functions
of
food
capture,
escape
from
predators,
migrat
ion,
and
so
on.
If
the
active
metabolism
is
not
sufficient
ly
high,
energy
is
not
available
for
feeding
activity
and,
subsequently,
growth
and
reproduction.
When
water
temperatures
rise
toward
lethal
conditions,
resting
metabolism
rate
increases
dramatically
and
feeding
rat
e
declines
to
zero.
When
water
temperatures
are
high,
most
of
the
fish's
assimilated
energy
may
be
required
simply
to
keep
up
with
basic
metabolic
demand.
When
active
metabolism
(
energy
expendit
ure
for
swimming)
declines
so
t
he
fish
can
divert
available
energy
to
basic
metabolic
demands,
feeding
declines.
And,
even
when
food
is
available,
feeding
no
longer
occurs
if
the
temperature
is
above
the
feeding
temperature
limit.
This
may
have
an
adaptive
benefit,
because
digesting
food
under
high
temperature
conditions
incurs
a
metabolic
demand
(
specific
dynamic
action).
The
more
overall
energy
the
fish
expends
in
basic
metabolism
and
food
digestion,
given
a
declining
food
intake,
the
lower
will
be
the
assimilated
energy
that
the
fish
can
utilize
for
growth,
reproduction,
or
resistance
to
environmental
extremes.
This
latter
use
of
energy
is
needed
for
resistance
to
disease
and
recuperation
from
cumulative
stresses
of
predator
avoidance,
migration,
high
temperature
stress,
and
so
on
(
Kelsch
1996).

Why
is
it
important
to
be
concerned
with
growth
rate,
production,
and
fish
density?

Production
is
the
elaboration
of
tissue
by
a
population
over
a
specified
period
of
time,
regardless
of
the
fate
of
the
tissue
(
Warren
1971).
Production
energy
is
stored
as
body
tissue
growth,
gametes,
or
released
as
secretions
(
e.
g.,
mucus).
Production
(
e.
g.,
growth)
for
any
time
period
in
which
growth
rate
is
relatively
constant
can
be
calculated
as
the
product
of
the
growth
rate
(
e.
g.,
mg/
g/
d)
and
mean
biomass
(
e.
g.,
g/
m2).
Production
for
longer
time
periods
is
calculated
as
the
summation
of
production
for
the
short
time
intervals
in
which
growth
rate
is
relatively
constant.
Production
can
also
be
computed
graphically
as
the
area
under
t
he
curve
where
number
of
individuals
in
the
population
at
an
instant
in
time
is
plotted
against
the
mean
weight
of
those
individuals
(
Warren
1971).
Regardless
what
method
is
used
to
calculate
production,
production
is
clearly
a
funct
ion
of
population
size,
survival,
and
growth
rate,
which
in
turn
may
be
influenced
by
water
temperature,
other
water
quality
factors,
food
availability,
level
of
predation,
and
so
on.

Temperature
regime
is
an
important
influence
on
fish
density.
Control
on
density
can
occur
through
a
combination
of
survival
effects,
behavioral
avoidance,
and
interspecific
competition.
Li
et
al.
(
1993)
reported
a
decline
in
steelhead
biomass
from
18
g/
m2
at
a
maximum
summer
water
temperature
of
60.8
°
F
(
16
°
C)
in
tributaries
of
the
John
Day
River
to
0
g/
m2
at
a
maximum
temperature
of
82.4
°
F
(
28
°
C).
The
sharp
reduction
in
biomass
with
increasing
temperature
is
an
indication
of
either
progressive
mortality
or
emigration
from
zones
exceeding
temperature
preferenda.
Likewise,
Ebersole
et
al.
(
in
press)
reported
for
tributaries
of
the
Grande
Ronde
River,
Oregon,
that
rainbow
trout
density
declined
steadily
between
a
mean
daily
maximum
40
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
temperature
of
53.6
°
F
(
12
°
C)
to
zero
at
approximately
75.2
°
F
(
24
°
C).
The
literat
ure
on
the
effect
of
water
temperature
in
controlling
fish
density
is
extensive
(
McCullough
1999).

Because
fish
are
mobile
and
migration
to
avoid
high
water
temperatures
is
sometimes
an
option,
it
is
not
easy
to
extrapolate
temperature­
fish
density
effects
to
a
whole
watershed
to
estimate
total
population
size
or
population
production.
Nonetheless,
the
numerous
studies
showing
a
decline
in
fish
density
with
increasing
water
temperature
probably
indicate
lethal
and
sublethal
effects
and
preference
for
habitats
in
which
growth
is
optimum
as
much
as
they
indicate
simple
avoidance
behavior.
Production
is
calculated
as
the
product
of
growth
rate
and
mean
biomass
(
see
above).
Energy
stored
as
production
is
distributed
primarily
in
somatic
growth
and
reproduction.
The
ability
to
divert
energy
to
reproduction
is
feasible
when
there
is
sufficient
scope
for
activity
and
this
depends
on
ambient
temperatures
and
food
availability.
In
addition,
population
viability
is
related
to
population
abundance.

What
is
the
optimum
range
o
r
optimum
temperature
for
growth
of
various
salmo
nids?

Chinook.
Chinook
production
in
an
experimentally
modeled
stream
at
53.6
°
F
(
12
°
C)
was
65%
higher
than
at
60.8
°
F
(
16
°
C)
(
Bisson
and
Davis
1976,
as
cited
by
CDWR
1988,
p.
31).
An
optimum
growth
temperature
of
59
°
F
(
15
°
C)
was
recommended
by
Banks
et
al.
(
1971
as
cited
by
Garling
and
Masterson
1985).
Brett
et
al.
(
1982)
recommended
58.6
°
F
(
14.8
°
C)
as
the
growth
optimum
for
juvenile
chinook
feeding
on
a
food
ration
of
60%
of
the
maximum
(
assumed
to
be
a
typical
level
in
nature).
Marine
and
Cech
(
1998)
determined
that
growth
rates
of
fall
chinook
under
sublethal
rearing
temperatures
(
69.8­
75.2
°
F
[
21­
24
°
C])
were
substantially
less
than
growth
rates
at
55.4­
60.8
°
F
(
13­
16
°
C).
Wilson
et
al.
(
1987)
recommended
50.9
°
F
(
10.5
°
C)
as
the
midpoint
of
the
growth
optimum
for
Alaskan
chinook,
based
on
studies
in
southeastern
and
southcentral
Alaska.
Preferred
rearing
temperatures
for
chinook
were
reported
as
high
as
58.3
°
F
(
14.6
°
C)
(
Reiser
and
Bjornn
1979).
The
preferred
temperature
range
for
fingerlings
was
53.6­
55.4
°
F
(
12­
13
°
C)
(
based
on
determination
of
mean
of
the
distribution)
when
the
fish
were
acclimated
to
temperatures
ranging
from
50
to
75.2
°
F
(
10­
24
°
C)
(
Brett
1952).
If
growth
temperatures
are
maintained
between
50
and
60
°
F
(
10­
15.6
°
C),
growth
rate
would
be
>
80%
of
the
maximum
level
observed
in
feeding
at
60%
satiation
(
a
level
considered
by
Brett
et
al.
[
1982]
to
correspond
to
naturally
occurring
food
availability
levels).
Growth
rate
under
60%
satiation
feeding
at
58.6
°
F
(
14.8
°
C)
is
expected
to
be
approximately
1.8%/
d
(
Brett
et
al.
1982).
Lower
levels
of
food
availability
would
reduce
the
optimum
growth
temperature.
Temperatures
above
60
°
F
(
15.6
°
C)
significantly
increase
the
risk
of
mortality
from
warm­
water
diseases.
A
synthesis
of
this
evidence
leads
t
o
a
recommended
optimum
production
temperature
zone
of
50­
60
°
F
(
10.0­
15.6
°
C).

The
optimal
growth
zone
of
50­
60
°
F
(
10­
15.6
°
C)
falls
within
the
range
for
positive
growth
at
40.1
°
F
(
4.5
°
C)
(
lower
limit)
and
66.4
°
F
(
19.1
°
C)
(
upper
limit)
(
see
Armour
1990).
The
39.4
and
66.4
°
F
(
4.1
and
19.1
°
C)
limits
tabulated
in
Armour
(
1990)
are
zero
net
growth
limits
for
a
chinook
population.
Brett
et
al.
(
1982)
reported
a
zero
individual
growth
rate
under
60%
satiation
feeding
at
70.5
°
F
(
21.4
°
C)
(
see
Figure
2).
If
chinook
were
to
have
unlimited
rations,
the
optimum
growth
temperature
would
be
approximately
66.2
°
F
(
19
°
C)
(
Brett
et
al.
1982).

Sockeye.
Good
growth
of
sockeye,
with
low
mortality,
occurred
at
53­
62
°
F
(
11.7­
16.7
°
C)
41
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
(
Donaldson
and
Foster
1941).
The
upper
limit
to
growth
was
similar
to
that
observed
by
Brett
et
al.
(
1982)
for
chinook
feeding
at
60%
of
satiation.
Sockeye
(
7­
12
months
old)
feeding
at
satiation
had
a
growth
rate
optimum
at
approximately
59
°
F
(
15
°
C).
Growth
rates
declined
at
both
higher
and
lower
temperatures.
Growth
rates
reached
zero
at
approximately
75.2
°
F
(
24
°
C)
under
satiation
feeding.
When
feeding
rate
was
lowered
to
1.5%/
d,
the
optimum
growth
temperature
declined
drastically
to
41
°
F
(
5
°
C).
At
this
feeding
rate,
growth
rate
(%/
d)
was
zero
at
approximately
59
°
F
(
15
°
C)
(
Brett
et
al.
1969).
Feeding
rat
es
of
Skaha
Lake
sockeye
at
62
°
F
(
16.7
°
C)
were
2.3%­
3.2%/
d
(
fresh
weight;
based
on
a
sample
of
the
2­
wk
periods
having
mean
temperatures
of
62
°
F
[
16.7
°
C]).
Feeding
rates
were
approximately
2.2%/
d
at
50
°
F
(
10
°
C),
but
the
optimum
growth
occurred
at
this
low
temperature
(
Donaldson
and
Foster
1941).
Optimum
Figure
2.
Optimum
growth
ra
tes
of
spring
ch
inook
under
various
feeding
regimes
and
constant
temperatures.

growth
temperature
was
59
°
F
(
15
°
C)
at
a
ration
of
6%/
d,
but
this
declined
to
an
optimum
growth
temperature
of
41
°
F
(
5
°
C)
at
a
ration
of
1.5%/
d
(
Brett
et
al.
1969).
42
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
Steelhead.
Wurtsbaugh
and
Davis
(
1977)
studied
growth
of
steelhead
trout
in
laboratory
streams
under
three
fluctuating
temperature
regimes
(
natural
cycle,
natural
+
5.4
°
F
[
3
°
C],
and
natural
+
10.8
°
F
[
6
°
C])
in
all
four
seasons
and
found
that
trout
growth
could
be
enhanced
by
temperature
increases
up
to
61.7
°
F
(
16.5
°
C).
During
the
summer
season
the
control
temperature
(
natural
cycle)
was
61.2
°
F
(
16.2
°
C)
(
mean)
and
the
elevated
temperatures
averaged
67.1
°
F
(
19.5
°
C)
and
72.5
°
F
(
22.5
°
C).
The
average
diel
temperature
range
for
the
summer
growth
period
was
about
38.1
°
F
(
3.4
°
C)
under
the
three
treatments.
Growth
rates
under
food
consumption
rates
of
5%­
15%
dry
body
wt/
d
were
higher
under
t
he
control
temperature
regime
than
at
the
elevated
fluctuating
regimes.
Under
the
high
temperature
regime
(
mean
of
72.5
°
F
[
22.5
°
C])
growth
rate
was
zero
at
a
food
consumption
rate
of
7%/
d.
Gross
food
conversion
efficiency
decreased
as
temperatures
increased
from
61.2
to
72.5
°
F
(
16.2­
22.5
°
C).
Maintenance
rations
increased
by
a
factor
of
three
over
the
temperature
range
44.4­
72.5
°
F
(
6.9­
22.5
°
C).

What
more
is
specifically
know
n
about
g
rowth
rea
ring
requirements
of
rainbow
trout?

Final
preferred
and
optimal
temperatures
for
rainbow
trout
have
been
reported
at
53.6­
66.2
°
F
(
12­
19
°
C)
(
Bell
1986,
Taylor
and
Barton
1992),
and
scope
of
activity
and
growth
for
juvenile
fish
are
commonly
reported
t
o
be
optimal
between
59
and
69.8
°
F
(
15­
21
°
C)
on
a
satiation
diet
(
Moyle
1976,
McCauley
and
Pond
1971,
Dickson
and
Kramer
1971,
Kwain
and
McCauley
1978,
and
Huggins
1978
as
cited
in
Kwain
and
McCauley
1978).
However,
some
authors
have
suggested
lower
optimal
temperature
ranges.
Piper
et
al.
(
1982)
set
the
optimal
at
50­
62.1
°
F
(
10­
16.7
°
C),
although
Sadler
et
al.
(
1986)
found
that
growth
and
food
conversion
efficiency
were
greater
at
60.8
°
F
(
16
°
C)
compared
with
50
°
F
(
10
°
C).
McCauley
and
Huggins
(
1975)
found
that
large
(
150­
250
g)
rainbow
trout
had
a
preferred
mean
temperature
of
62.1
°
F
(
16.7
°
C),
and
that
t
he
fish
actively
traveled
at
temperatures
between
56.8
and
64.4
°
F
(
13.8­
18
°
C)
in
a
thermal
gradient.
Behnke
(
1992)
suggested
that
the
optimum
temperature
for
growth
and
food
assimilation
in
salmonids
occurs
between
55.2
and
60.8
°
F
(
13­
16
°
C).
Ferguson
(
1958)
cites
56.5
°
F
(
13.6
°
C)
as
the
final
preferred
temperature
for
rainbow
trout,
and
Mckee
and
Wolf
(
1963,
cited
in
Wedemeyer
et
al.,
no
date)
found
55.4
°
F
(
13
°
C)
to
be
optimum.
Kwain
and
McCauley
(
1978)
suggest
t
hat
fish
over
1
year
old
may
have
a
final
preferred
temperature
of
55.4
°
F
(
13
°
C)
(
cit
ing
the
works
of
Garside
and
Tait
1958,
Christ
ie
as
reported
in
Fry
1971,
and
McCauley
et
al.
1977,
as
cited
in
Kwain
and
McCauley
1978)
although
as
noted
above,
the
work
of
McCauley
and
Huggins
(
1975)
suggests
that
older
fish
sometimes
demonstrate
more
intermediate
temperature
preferences.

Dockray
et
al.
(
1996)
found
that
in
a
fluctuating
temperature
environment,
temperature
increases
benefited
growth
up
to
daily
maximum
temperatures
of
64.4
°
F
(
18
°
C),
above
which
long­
term
growth
was
inhibited.
De
Leeuw
(
1982)
found
that
stream
temperature
increases
that
raised
the
summertime
maximum
temperature
from
53.6
to
61.7
°
F
(
12­
16.5
°
C)
were
associated
with
an
increase
in
growth
rates
in
three
streams
in
British
Columbia,
Canada.
Hokanson
et
al.
(
1977)
found
that
a
constant
exposure
to
63
°
F
(
17.2
°
C)
produced
the
greatest
growth
rates
in
trout
fed
to
satiation
over
a
40­
d
test
period.
Increased
mortality
was
observed
in
temperatures
above
this
growth
optimum.
They
also
noted
that
in
fluctuating
temperature
experiments,
growth
was
accelerated
when
the
mean
temperature
was
below
the
const
ant
temperature
optimum
(
63
°
F
[
17.2
°
C]),
and
growth
was
retarded
by
mean
fluctuating
temperatures
above
this
optimum.
The
highest
growth
rate
in
the
fluctuat
ing
temperature
environment
occurred
at
a
mean
of
59.9
°
F
43
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
(
15.5
°
C)
(
range
of
53­
66.7
°
F
[
11.7­
19.3
°
C]).
A
statistically
nonsignificant
decrease
occurred
at
a
mean
of
63.1
°
F
(
17.3
°
C)
(
range
of
56.3­
70
°
F
[
13.5­
21.1
°
C]).
The
authors
also
concluded
that
rainbow
trout
acclimate
to
some
temperature
between
the
mean
and
the
maximum
daily
temperatures.
Sometimes,
warmer
waters
may
provide
secondary
benefits
to
rainbow
trout.
Cunjak
and
Green
(
1986)
found
that
rainbow
trout
were
able
to
compete
better
with
brook
trout
at
66.2
°
F
(
19
°
C)
than
at
either
46.4
or
55.4
°
F
(
8
or
13
°
C).

Bisson
and
Davis
(
1976,
as
cited
in
Li
et
al.
1994)
found
that
streams
with
daily
maximum
temperatures
of
60.8­
73.4
°
F
(
16­
23
°
C)
had
greater
standing
crops
of
trout
than
did
streams
with
warmer
maximum
temperatures
(
78.8­
87.8
°
F
[
26­
31
°
C]).
Frissell
et
al.
(
1992)
studied
the
distribution
of
rainbow
trout
and
found
that
although
they
could
be
found
in
water
temperatures
over
73.4
°
F
(
23
°
C),
there
was
a
general
threshold
response
for
age
1+
fish
above
71.6
°
F
(
22
°
C)
and
for
age
2+
fish
above
69.8
°
F
(
21
°
C).
Consistent
with
these
results,
Li
et
al.
(
1993,
1994,
and
1991
as
cited
in
Spence
et
al.
1996)
noted
that
even
though
rainbow
trout
might
not
show
avoidance
reactions
when
stream
temperatures
were
below
68
°
F
(
20
°
C),
they
actively
avoided
waters
warmer
than
73.4­
77
°
F
(
23­
25
°
C).
Linton
et
al.
(
1997)
noted
that
rainbow
trout
fed
to
satiation
continued
to
feed
and
grow
at
a
mean
temperature
of
68.9
°
F
(
20.5
°
C),
a
30%
reduction
in
food
intake
occurred
at
71.6
°
F
(
22
°
C),
and
juvenile
fish
continued
to
feed
near
their
thermal
maximum.
Linton
et
al.
(
1997)
found
that
increasing
the
temperature
regime
by
3.6
°
F
(
2
°
C)
over
the
natural
(
base)
level
for
Lake
Ontario
trout
resulted
in
increased
spring
and
early
summer
growth,
which
was
lost
later
in
the
summer
due
to
suppression
of
appetite
and
growth.
Mortality
rates
increased
from
6%
to
13.1%
in
the
warmer
test
water
during
the
late
summer
in
the
first
summer
of
testing
when
the
mean
monthly
base
temperature
in
August
was
73.4
°
F
(
23
°
C).
Mortality
was
almost
nonexistent
through
the
following
summer,
which
had
a
mean
August
base
temperature
of
64.4
°
F
(
18
°
C)
(
the
test
wat
ers
should
have
had
a
mean
of
68
°
F
[
20
°
C]).
The
threshold
temperature
for
cessation
of
feeding,
and
subsequently
growth,
differed
from
>
68
°
F
(
20
°
C)
to
<
68
°
F
(
20
°
C)
over
the
two
summers,
and
thus
also
fish
size
and
age.
Behnke
(
1992)
cited
work
showing
that
trout
reduce
and
finally
cease
feeding
as
temperatures
rise
to
between
71.6
and
77
°
F
(
22­
25
°
C),
often
well
below
the
lethal
temperature.

Although
the
works
of
Li
et
al.
(
1991,
1993,
1994)
cited
above
were
conducted
on
interior
forms
of
rainbow
trout,
Behnke
(
1992)
reported
finding
redband
trout
in
the
desert
basins
of
southern
Oregon
and
northern
Nevada
where
temperatures
regularly
kill
other
trout.
Trout
in
these
intermittent
desert
streams
were
found
actively
feeding
in
water
of
82.9
°
F
(
28.3
°
C).
Behnke
suggested
that
redband
trout
from
an
Oregon
desert
basin
have
an
optimum
feeding
temperature
at
some
untested
temperature
higher
than
66.2
°
F
(
19
°
C).
These
desert
redband
might
have
a
functional
feeding
temperature
that
is
higher
than
that
of
rainbow
trout,
which
have
evolved
in
less
harsh
environments
of
temperature
and
water
flow.
A
test
was
evaluated
that
compared
an
introduced
population
of
rainbow
trout
in
the
Firehole
River
in
Montana
with
two
hatchery
stocks.
Temperatures
in
the
Firehole
River
in
summer
at
times
reached
as
high
as
85.1
°
F
(
29.5
°
C)
due
to
thermal
springs.
The
introduced
population
had
been
living
in
the
river
for
approximately
20
generations,
yet
it
was
found
that
neither
the
functional
feeding
temperature
nor
the
upper
incipient
lethal
temperature
had
increased
compared
with
the
hat
chery
stocks.
The
author
concluded
that
thousands
of
years
of
adaptation
to
a
dry
environment
have
enabled
Oregon
desert
redband
trout
to
feed
at
high
temperatures,
but
60­
70
years
seem
too
few
to
have
allowed
the
introduced
rainbow
trout
to
raise
their
functional
feeding
temperature
in
the
Firehole
River.
44
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
Kaya
et
al.
(
1977)
found
that
daily
maximum
temperatures
exceeding
77
°
F
(
25
°
C)
caused
rainbow
trout
to
move
out
of
the
mainstem
of
the
Firehole
River
in
Montana.
These
fish
would
move
into
tributary
streams
that
averaged
10.8­
18
°
F
(
6­
10
°
C)
lower
in
temperature.

The
above
research
shows
a
wide
range
in
the
estimates
of
optimal
temperature
for
rearing
rainbow
trout.
This
wide
range
may
reflect
the
fact
that
the
individual
subspecies
and
specific
stocks
have
evolved
differently
to
fit
the
charact
eristics
of
their
home
streams.
Also,
different
ages
and
sizes
of
fish
were
used
in
the
research.
Equally
plausible
is
that
some
of
the
temperatures
for
redband
trout
that
were
higher
than
noted
for
rainbow
trout
or
other
salmonids
might
have
been
based
on
an
improper
assumption
that
temperatures
measured
in
the
vicinity
of
the
fish
were
actually
those
that
the
fish
inhabited
 
that
is,
fish
might
actually
inhabit
microhabitat
or
habitat­
scale
refugia
to
maintain
their
populations
in
otherwise
hostile
conditions
(
see
Ebersole
et
al.
in
press).
Because
criteria
must
protect
bot
h
adult
and
juvenile
forms
of
rainbow
trout,
an
optimal
temperat
ure
regime
seems
to
most
consistently
occur
in
the
range
o
f
55.4­
60.8
°
F
(
13­
16
°
C).

What
is
the
relationship
between
growth
temperatures
and
other
physiological
responses?

When
fish
demonstrate
temperature
preference
in
a
thermal
gradient,
this
is
an
adaptive
mechanism
that
allows
them
to
be
positioned
in
an
environment
where
they
can
achieve
optimum
physiological
performance
(
Coutant
1987,
Hutchison
and
Maness
1979).
Hutchison
and
Maness
(
1979)
cited
numerous
physiological
processes
t
hat
achieve
optimum
performance
near
the
thermal
preferendum:
growth
rate,
appetite,
food
conversion
efficiency,
digestion,
egestion,
metabolic
scope,
oxygen
debt
load,
maximum
sustained
speed,
maximum
volitional
speed,
resting
and
active
blood
pressure,
active
cardiac
work,
cardiac
scope,
learning
and
memory,
immune
response,
renal
function,
hormone
secretion,
reproductive
function,
elimination
of
anaerobically
produced
lactate,
and
enzyme
act
ivity.

Temperatures
preferred
or
avoided
are
highly
correlated
with
key
physiological
indices
(
Stauffer
1980).
Final
temperature
preference
is
correlated
with
optimal
growth
temperature
(
Jobling
1981,
Kellogg
and
Gift
1983,
Christie
and
Regier
1988).
Kellogg
and
Gift
(
1983)
found
for
four
fish
species
that
nearly
all
preferred
temperatures
measured
were
in
a
range
that
provided
75%
of
maximum
growth
rate.
The
physiological
optimum
is
derived
by
averaging
the
growth
optimum
and
preferred
temperature
(
Brett
1971).
Preferred
temperature
also
is
correlated
with
the
temperature
providing
the
maximum
metabolic
scope.
This,
in
turn,
is
related
to
the
temperature
providing
the
maximum
critical
swimming
speed
(
Kelsch
and
Neill
1990).
Also,
fish
tend
to
be
more
immunologically
resistant
to
pathogens
at
their
preferred
temperatures
(
Sniezko
1974,
Cuchens
and
Clem
1977,
Avtalion
et
al.
1980,
O'Neil
1980,
Rijkers
et
al.
1980,
Avtalion
1981,
Wishkovsky
and
Avtalion
1982,
all
cited
in
ODEQ
1995).

The
preferred
temperature
range
for
chinook
fingerlings
was
53.6­
55.4
°
F
(
12­
13
°
C)
(
based
on
determination
of
mean
of
the
distribution)
when
acclimated
to
temperatures
ranging
from
50
to
75.2
°
F
(
10­
24
°
C)
(
Brett
1952).
If
growth
temperatures
are
maintained
between
50
and
60
°
F
(
10­
15.6
°
C),
growth
rate
would
be
>
80%
of
the
maximum
level
observed
in
feeding
at
60%
satiation
(
a
level
considered
by
Brett
et
al.
[
1982]
to
correspond
to
naturally
occurring
food
availability
45
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
levels).

For
sockeye,
Brett
(
1971)
found
that
swimming
capacity,
metabolic
scope,
growth
on
excess
rations,
and
ingestion
were
maximized
at
59
°
F
(
15
°
C).
The
temperature
producing
the
growth
optimum
(
59
°
F
[
15
°
C])
also
was
the
final
thermal
preferendum
determined
by
acute
tests
(
Brett
1952,
1971).
A
correlation
between
final
preferred
temperature
and
optimum
growth
has
been
found
in
numerous
other
fish
species
(
Christie
and
Regier
1988).
In
coho,
it
was
found
that
swimming
speed
was
maximum
at
68
°
F
(
20
°
C),
but
growth
reached
a
maximum
on
excess
food
rations
at
62.6­
68
°
F
(
17­
20
°
C)
(
Griffiths
and
Alderdice
1972).

What
are
temperature
feeding
limits
for
salmonids?

Temperature
feeding
limits
are
the
upper
and
lower
temperatures
that
result
in
inhibition
of
feeding.
The
ability
to
consume
food
does
not
guarantee
that
growth
occurs.
Food
intake
rate
and
conversion
efficiency
(
assimilation
rate)
at
any
temperature
dictate
the
amount
of
energy
assimilated.
However,
if
metabolism
rate
exceeds
energy
assimilation
rate,
no
energy
is
available
for
growth.
In
fact,
the
fish
would
lose
weight
because
energy
stored
in
tissue
is
used
for
metabolism.

Brett
et
al.
(
1982)
o
bserved
feeding
behavior
of
juvenile
chinook
from
the
Nechako
River,
in
British
Columbia,
and
the
Big
Qualicum
River,
on
Vancouver
Island.
They
reported
good
feeding
response
to
unlimited
food
supply
at
71.6
°
F
(
22
°
C),
but
feeding
became
more
sporadic
between
73.4
and
77
°
F
(
23­
25
°
C),
at
which
point
it
ceased.

Fingerling
sockeye
began
losing
appetite
at
73.9
°
F
(
23.3
°
C)
and
stopped
feeding
at
75.2
°
F
(
24
°
C).
Maximum
feeding
rate
was
measured
as
8%
dry
body
wt/
d
at
68
°
F
(
20
°
C).
Redband
trout
can
be
expected
to
set
the
upper
limit
for
feeding
response
for
all
salmonids
of
the
Pacific
Northwest.
No
feeding
was
observed
by
Sonski
(
1982
as
cited
by
Sonski
1984)
for
juvenile
redband
at
77.9­
80.6
°
F
(
25.5­
27
°
C).
Comparing
thermal
tolerance
by
three
rainbow
trout
species,
Sonski
(
1984)
found
that
no
redband
trout
or
Wytheville
rainbow
would
feed
at
temperatures
>
78.8
°
F
(
26
°
C).
The
Firehole
River
stock
would
not
feed
beyond
80
°
F
(
26.7
°
C).

In
CTM
(
critical
thermal
maximum)
experiments
in
which
the
heating
rate
was
3.6
°
F
(
2
°
C)/
d,
five
species
of
juvenile
salmonids
were
observed
feeding
up
to
temperatures
that
were
1.8­
3.6
°
F
(
1­
2
°
C)
less
than
the
LT50
(
Grande
and
Anderson
1991).
Lake
trout,
brook
trout,
brown
trout,
rainbow
trout,
and
Atlantic
salmon
were
observed
feeding
at
temperatures
of
74.8,
78.2,
79.1,
79.9,
and
82.6
°
F
(
23.8,
25.7,
26.2,
26.6,
and
28.1
°
C),
respect
ively,
reached
during
CTM
experiments.
A
similar
CTM
experiment
with
Salmo
apache
in
which
temperature
was
increased
1.8­
2.7
°
F
(
1­
1.5
°
C)/
d
showed
that
fish
began
refusing
food
at
68
°
F
(
20
°
C)
and
t
otally
stopped
feeding
at
70.1
°
F
(
21.2
°
C)
(
Alco
rn
1976).
In
no
rthern
California
streams,
juvenile
steelhead
were
seen
actively
feeding
in
water
temperatures
as
high
as
75.2
°
F
(
24
°
C)
(
Nielsen
et
al.
1994).
However,
once
temperatures
reached
71.6
°
F
(
22
°
C),
rate
of
foraging
began
to
decline.

How
is
feeding
rate
affected
by
acclimation
temperature?

The
highest
temperature
for
normal
feeding
in
brown
trout
varies
with
acclimation
46
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
temperature,
as
is
probable
for
all
fish
species.
Elliott
(
1981)
determined
that
the
highest
temperature
for
normal
feeding
in
brown
trout
that
were
acclimated
to
59
°
F
(
15
°
C)
was
19.1
°
C
±
0.27
(
SE).
Similarly,
Frost
and
Brown
(
1967)
determined
that
feeding
rate
declined
sharply
above
66.2
°
F
(
19
°
C)
in
brown
trout.
When
fish
were
acclimated
to
68
°
F
(
20
°
C),
no
feeding
took
place.
Under
cold
temperature
regimes,
when
brown
trout
were
acclimated
to
water
at
50
°
F
(
10
°
C),
normal
feeding
occurred
when
fish
were
subjected
to
2.9
°
C
±
0.27.
When
acclimated
to
even
lower
temperature
41
°
F
(
5
°
C),
normal
feeding
occurred
at
0.4
°
C
±
0.21.

What
are
temperature
growth
limits
for
salmonids?

Temperature
growth
limits
for
salmonids
are
those
lower
and
upper
temperatures
that
result
in
zero
growth
on
an
individual
basis
or
zero
net
growth
of
the
population.
The
zero
net
growth
temperature
is
the
temperature
at
which
net
elaborat
ion
of
tissue
of
the
population
is
zero
o
r
the
temperature
at
which
fish
mortality
balances
the
gain
in
growth.

With
chinook,
the
bounds
for
positive
growth
occur
at
40.1
°
F
(
4.5
°
C)
(
lower
limit)
and
66.4
°
F
(
19.1
°
C)
(
upper
limit)
(
see
Armour
1990).
The
39.4
°
F
(
4.1
°
C)
and
66.4
°
F
(
19.1
°
C)
limits
tabulat
ed
in
Armour
(
1990)
are
zero
net
growth
limits
for
a
chinook
population.
Bret
t
et
al.
(
1982)
reported
a
zero
individual
growth
rate
under
60%
satiation
feeding
at
70.5
°
F
(
21.4
°
C).

Juvenile
sockeye
had
a
positive
growth
response
between
39.2
and
69.8
°
F
(
4­
21
°
C)
in
laboratory
experiments
with
feeding
to
satiation
once
per
day
(
Donaldson
and
Foster
1941).
Growth
rate
was
negative
at
73
°
F
(
22.8
°
C),
and
at
this
temperature
mortality
was
significant.
Good
growth
with
low
mortality
occurred
at
53­
62
°
F
(
11.7­
16.7
°
C)
(
Donaldson
and
Foster
1941).
The
upper
limit
to
growth
was
similar
to
that
observed
by
Brett
et
al.
(
1982)
for
chinook
feeding
at
60%
of
satiation
rations.

Brown
trout
growth
can
be
high
in
the
temperature
range
44.6­
66.2
°
F
(
7­
19
°
C),
but
growth
is
poor
above
68
°
F
(
20
°
C)
(
Frost
and
Brown
1967).

Wurtsbaugh
and
Davis
(
1977)
studied
growth
of
steelhead
trout
in
laboratory
streams
under
three
fluctuating
temperature
regimes
(
natural
cycle,
natural
+
5.4
°
F
[
3
°
C],
and
nat
ural
+
10.8
°
F
[
6
°
C])
in
all
four
seasons
and
found
that
trout
growth
could
be
enhanced
by
temperature
increases
up
to
61.7
°
F
(
16.5
°
C).
During
the
summer
season
the
control
temperature
(
natural
cycle)
was
61.1
°
F
(
16.2
°
C)
(
mean)
and
the
elevated
temperatures
averaged
67.1
and
72.5
°
F
(
19.5
and
22.5
°
C).
The
average
diel
temperature
range
for
the
summer
growth
period
was
about
6.1
°
F
(
3.4
°
C)
under
the
three
treatments.
Growth
rates
under
food
consumption
of
5%­
15%
dry
body
wt/
d
were
higher
under
the
control
temperature
regime
than
at
the
elevated
fluctuating
regimes.
Under
the
high
temperature
regime
(
mean
of
72.5
°
F
[
22.5
°
C]),
growth
rate
was
zero
at
a
food
consumption
rate
of
7%/
d.

How
does
food
availability
affect
growth
of
salmonids
at
different
temperature
exposures?

In
a
laboratory
setting,
feeding
rations
can
be
controlled
by
the
researchers.
Feeding
to
satiation
at
a
frequency
of
three
to
five
times
a
day
is
not
uncommon
in
growth
experiments
and
is
47
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
considered
to
provide
growth
rates
comparable
to
those
under
continuous
feeding
with
excess
food.
In
other
studies,
varying
feeding
regimes
may
be
used
to
determine
the
temperature
effects
on
growth
at
different
levels
of
food
availability.

In
the
field,
stream
productivity
and
nutrient
availability
to
salmonids
depend
on
many
factors
including
light;
nutrients
including
inputs
of
litter,
decomposing
salmon
carcasses,
and
coarse
woody
debris;
sediment
loading;
temperature;
and
streamflow
(
Murphy
1998,
Bilby
et
al.
1996).
Other
factors
t
hat
may
limit
fish
feeding
in
the
wild
include
suitable
instream
cover
and
species­
or
density­
dependent
competition
and
predation
(
Richardson
1993).

Food
limitations
in
trout
streams
commonly
cause
reductions
in
summer
growth
(
Cada
et
al.
1987,
Enseign
and
Strange
1990).
If
there
is
food
limitation
in
the
field,
growth
rates
will
be
less
than
maximum
for
salmon
and
bull
trout
at
temperatures
that
produce
maximum
growth
under
satiation
feeding.
Growth
rates
have
been
observed
in
the
field
that
are
less
than
those
predicted
in
the
labo
ratory
under
excess
feeding
and
suggest
t
hat
food
limitation
could
be
the
cause
(
Preall
and
Ringler
1989,
Cada
et
al.
1987).
With
food
limitation,
the
upper
temperature
that
produces
zero
growth
would
decline
to
a
lower
temperature.
Under
conditions
where
fish
have
reduced
feeding
rates
due
to
food
limitation,
conversion
efficiency
can
increase
somewhat
to
compensate
for
the
limitation
in
total
energy
intake.
However,
if
the
food
limitation
is
significant,
the
energy
demands
of
standard
metabolism
may
be
difficult
to
satisfy
(
Cada
et
al.
1987).
This
may
limit
the
scope
of
activity
required
to
acquire
food.
Behavioral
inhibition
in
swimming
at
higher
temperatures
and
lack
of
competitive
ability
in
foraging
compared
with
fish
tolerant
of
warm
water
can
place
salmonids
at
a
disadvantage
in
deriving
maintenance
energy
requirements.

Gut
fullness
may
be
an
indicator
of
food
availability.
Gut
fullness
was
monitored
on
several
fish
species
on
various
dates
from
late
July
to
mid­
October
in
several
tributaries
of
the
upper
Yakima
River
as
an
index
of
food
availability
(
James
et
al.
1998).
During
this
sampling
period,
temperatures
were
>
57.2
°
F
(
14
°
C).
Species
monitored
included
mountain
whitefish,
spring
chinook,
redside
shiner,
and
rainbow
trout.
A
high
degree
of
diet
overlap
was
found
among
the
four
fish
species
studied,
indicating
that
competition
for
food
is
possible.
Gut
fullness
and
diet
overlap
together
were
assumed
to
indicate
degree
of
competition.
Summertime
gut
fullness
for
spring
chinook
averaged
14%,
while
mountain
whitefish,
rainbow
trout,
and
redside
shiner
averaged
32%,
10%,
and
10%,
respectively.
Low
stomach
fullness
may
indicate
a
low
availability
of
food
due
t
o
production
of
food
and
intense
competition.
It
is
not
clear
from
this
research,
however,
what
gut
fullness
level
would
be
expected
under
satiation
feeding.
Growth
rates
are
the
bottom
line.
Comparison
of
growth
rates
at
various
feeding
levels
in
t
he
laboratory
with
rat
es
in
the
field
under
comparable
temperat
ures
appears
to
be
the
most
direct
means
to
infer
food
supply.

If
food
becomes
limited,
the
positive
growth
zone
can
shrink
dramatically
(
i.
e.,
the
maximum
temperature
at
which
growth
is
positive
declines)
and
the
optimum
growth
zone
shifts
to
lower
temperatures
to
compensate
for
elevated
respiration/
growth
ratios
(
Elliott
1981,
p.
231).
McMahon
et
al.
(
1999)
found
that
growth
curves
for
bull
trout
clearly
depict
a
shift
to
maximum
growth
at
lower
temperatures
(
46
and
53
°
F
[
8
and
12
°
C])
when
energy
availability
is
low.
Elliott
found
that
for
brown
trout
the
temperature
at
which
growth
is
zero
drops
from
66.2
to
46.4
°
F
(
19­
8
°
C)
when
food
rations
are
reduced
from
maximum
to
12.5%
of
maximum.
Because
the
growth
optimum
falls
within
50­
60
°
F
(
10­
15.6
°
C)
for
chinook
and
because
diseases
become
a
48
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
significant
mortality
risk
beyond
this
level,
water
temperatures
in
major
salmon­
rearing
reaches
must
be
managed
on
a
stream
network
level
from
headwaters
to
mainstem
so
that
temperatures
can
be
maintained
below
60
°
F
(
15.6
°
C)
within
the
hist
oric
salmon
rearing
area
and
below
53.6
°
F
(
12
°
C)
in
bull
trout
historic
rearing
areas.
Given
that
food
rations
under
field
conditions
are
typically
less
than
satiation
levels,
a
reduced
growth
zone
expands
the
upper
temperature
zone
and
causes
loading
stresses.
This
argues
for
keeping
temperatures
no
higher
than
the
optimum
growth
range.

Is
there
evidence
for
food
limitation
in
natural
streams?

A
stream's
capacity
to
produce
food
greatly
affects
both
abundance
and
growth
of
fish.
Some
of
the
highest
freshwater
production
value
have
been
reported
for
trout
in
New
Zealand;
production
values
reported
for
the
Pacific
Northwest
are
considerably
lower,
by
at
least
an
order
of
magnitude
(
Bisson
and
Bilby
1998).

Factors
influencing
stream
productivity
include
nutrient
availability,
input
of
organic
matter
from
external
sources,
the
channel's
capacity
to
store
and
process
organic
matter,
and
light
(
Cederholm
et
al.
2000).
The
river
continuum
concept
describes
the
predictable
differences
in
stream
productivity
with
changes
in
stream
size
(
Vannote
et
al.
1980).
Headwater
streams
in
the
Pacific
Northwest
are
characterized
by
low
levels
of
primary
and
secondary
productivity
(
Gregory
et
al.
1987).
In
a
large
watershed,
first­
to
third­
order
streams
may
produce
only
10%­
20%
of
the
annual
gross
primary
production,
despite
having
more
than
80%
of
total
stream
length
(
Murphy
1998).
Coho,
steelhead,
cutthroat,
bull
trout,
and
spring
chinook
are
among
the
salmonids
that
utilize
these
small
headwater
streams
for
spawning
and
rearing.

Productivity
of
Northwest
streams
has
been
further
diminished
by
the
recent
decline
of
Pacific
salmon.
The
role
salmon
populations
play
in
maintaining
ecosystem
function
by
recycling
energy
and
nutrients
from
the
North
Pacific
Ocean
to
the
inland
Northwest
has
been
acknowledged
in
numerous
studies
(
see
Cederhom
et
al.
2000).
The
carcasses
of
spawned­
out
salmon
greatly
influence
the
productivity
of
the
otherwise
generally
oligotrophic
ecosystems
of
the
Pacific
Northwest
(
Cederholm
et
al.
2000).
With
declines
of
Pacific
salmon,
it
is
estimated
that
only
3%
of
the
marine­
derived
biomass
once
delivered
by
anadromous
salmon
to
the
rivers
of
Puget
Sound,
the
Washington
coast,
the
Columbia
River,
and
the
Oregon
coast
is
currently
reaching
those
streams
(
Gresh
et
al.
2000
in
Cederholm
et
al.
2000).

Growth
rates
of
wild
rainbow
trout
in
the
field
have
generally
been
reported
as
<
1%/
d
(
see
review
by
Wurtsbaugh
and
Davis
1977)
but
were
higher
in
the
laboratory
in
every
season
under
the
natural
temperature
regime
(
mean
seasonal
temperatures
in
the
laboratory
of
50,
44.4,
48.9
and
61.1
°
F
[
10,
6.9,
9.4,
and
16.2
°
C]
in
autumn,
winter,
spring,
and
summer,
respectively)
when
fish
were
fed
t
o
satiation.
This
study
revealed
that
trout
growth
was
improved
by
increasing
temperatures
up
to
a
maximum
of
61.7
°
F
(
16.5
°
C),
but
that
this
threshold
applies
to
the
field
only
under
satiation
feeding.
Because
the
researchers
measured
field
growth
rates
in
an
Oregon
coast
al
stream
that
indicated
food
limitation,
they
concluded
that
temperatures
less
than
61.7
°
F
(
16.5
°
C)
would
be
optimal.

In
the
field
an
increase
in
water
temperature,
when
produced
by
canopy
removal,
can
lead
to
49
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
increased
primary
production.
Greater
primary
and
secondary
production
can
increase
food
availability
to
fish
(
Murphy
and
Hall
1981,
Hawkins
et
al.
1983)
provided
that
substrate
sedimentation
does
not
increase
with
canopy
removal.
However,
as
temperatures
continue
to
increase,
primary
production
can
be
in
the
form
of
algae
not
readily
consumed
or
digested
by
benthic
macroinvertebrates
(
e.
g.,
blue­
green
algae
rather
than
diatoms)
(
McCullough
1975,
McCullough
et
al.
1979),
and
macroinvertebrate
production
can
be
dominated
by
species
not
readily
available
to
salmonids
in
the
drift
(
Li
et
al.
1994).
Even
if
food
quality
remains
high
with
increasing
temperature,
feeding
rate
and
growth
decline
beyond
the
optimum
temperature.
Additionally,
over
the
long
run,
increases
in
primary
production
in
early
seral
stage
may
eventually
be
outweighed
by
longer­
lasting
reductions
as
a
result
of
increased
shade
in
later
seral
stages
(
Murphy
and
Hall
1981).
Second­
growth
hardwoods
and
young
conifers
produce
a
denser
canopy
and
lack
the
gaps
commonly
found
in
old­
growth
forests
(
Murphy
1998).

Can
growth
rates
be
predicted
under
field
conditions
using
thermal
history
identified
under
laboratory
conditions?

Growth
rates
under
controlled
field
conditions
can
be
related
to
growt
h
rates
obtained
under
laboratory
conditions
if
feeding
rates
and
temperatures
are
known;
however,
many
subtle
variables
in
the
field
(
recruitment
to
or
movement
out
of
the
study
area,
varied
caloric
content
of
forage,
inter­
and
intraspecies
interactions)
can
complicate
these
comparisons.
Differences
between
laboratory
and
field
growth
rates
can
be
attributable
to
a
great
number
of
factors.

Typically,
temperatures
in
laboratory
experiments
are
kept
constant
(
i.
e.,
fluctuating
less
than
±
1.8
°
F
[
1
°
C]
around
the
mean).
First,
to
compare
laboratory
and
field
growth
rate
we
must
know
the
field
water
temperature
regime.
Growth
rates
should
be
measured
over
days
to
weeks
to
improve
the
ability
to
detect
a
change.
The
temperature
regime
must
be
described
by
an
index
(
e.
g.,
daily
mean,
daily
maximum)
in
order
to
relate
it
to
laboratory
growth
rates.
For
example,
if
growth
rate
under
a
constant
laboratory
temperature
o
f
50
°
F
(
10
°
C)
is
2%/
d
and
under
field
conditions
a
2%/
d
growth
rate
is
experienced
by
fish
under
a
50
°
F
(
10
°
C)
±
3.6
°
F
(
2
°
C)
diel
temperature
regime,
then
we
might
conclude
that
the
mean
diel
temperature
in
the
field
adequately
represents
the
growth
conditions.
However,
food
is
generally
limiting
in
the
field.
If
this
is
the
case
and
if
the
mean
field
temperature
adequately
represents
the
growth
response,
we
would
expect
field
growth
rate
to
be
lower
than
laboratory
rates
at
the
same
constant
mean
temperature.
The
situation
can
be
more
complicated,
however,
because
growth
rate
is
related
to
acclimation
temperature.
In
a
fluctuating
temperature
regime,
fish
can
acclimate
to
a
temperature
between
the
mean
and
maximum
of
the
cycle.
If
this
is
so,
the
feeding
rate
in
the
field
(
and
consequently
growth
rate)
might
be
higher
than
under
a
const
ant
diel
temperature
equal
to
the
mean
of
the
cycle,
despite
the
lower
food
availability.
That
is,
there
may
be
some
compensation
for
lower
food
availability
due
to
fluctuating
temperature
conditions.
In
summary,
field
growth
depends
on
the
food
availability
and
quality,
the
effect
ive
acclimation
temperature,
and
the
exposure
temperature.

The
ability
to
model
brown
trout
growth
in
the
laboratory
and
field
under
fluctuat
ing
temperatures
arose
from
Elliott's
(
1975a,
b)
studies
of
brown
trout
growth
under
constant
temperatures.
This
model
has
often
been
found
capable
of
predicting
growth
under
both
constant
and
fluctuating
temperatures
(
Elliott
1994).
Elliott
(
1975a)
found
that
growth
rates
in
the
50
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
laborat
ory
over
42­
d
periods
in
which
temperature
fluctuated
as
much
as
±
4.1
°
F
(
2.3
°
C)
around
the
mean
for
the
entire
period
closely
matched
those
predicted
by
entering
the
mean
temperature
into
the
growth
model.
Growth
experiments
in
the
field
(
a
small
stream
near
Windermere,
England)
were
also
conducted.
In
one
experiment,
temperature
increased
from
44.2
°
F
(
6.8
°
C)
in
March
to
53.8
°
F
(
12.1
°
C)
in
June;
in
another,
temperature
decreased
from
55.2
°
F
(
12.9
°
C)
in
August
to
45
°
F
(
7.2
°
C)
in
November.
Estimates
of
growth
in
the
field
made
by
entering
the
mean
weekly
temperatures
(
calculated
as
the
mean
of
seven
daily
mean
temperatures)
into
the
growth
model
revealed
good
agreement
between
predicted
and
actual
final
weights
in
a
4­
wk
growth
period.
Edwards
et
al.
(
1979)
modeled
brown
trout
growth
on
10
British
streams
and
were
able
to
show
that
predicted
growth
was
60%­
90%
of
potential
growth,
assuming
feeding
on
maximum
rations.
Predicted
monthly
growth
based
on
mean
monthly
temperatures
was
2%
different
from
computations
based
on
temperatures
taken
every
4
h.
Likewise,
Preall
and
Ringler
(
1989)
developed
a
computer
model
of
brown
trout
growth
based
on
Elliott's
work
and
predicted
potential
growth
for
populations
in
three
central
New
York
streams
based
on
initial
weight,
condition
factor,
and
weekly
mean
temperature.
These
authors
measured
actual
growth
under
fluctuating
temperatures
in
the
field
that
were
60%­
90%
of
potential,
as
determined
from
their
model.
Jensen
(
1990)
measured
growth
on
12
populations
in
Norwegian
rivers
and
determined
that
mean
growth
rates
of
anadromous
brown
trout
parr
were
76%­
136%
of
the
maximum
inferred
from
the
temperature
regime.

Jensen
(
1990)
concluded
from
his
field
work
that
growth
rates
exceeding
laboratory­
derived
maxima
under
constant
temperatures
and
satiation
feeding
could
be
explained
by
interpopulation
genetic
differences
o
r
the
ability
of
fish
in
the
field
to
feed
at
great
er
rates
under
fluctuating
temperatures
than
under
constant
temperatures.
It
is
also
possible
that
the
ability
to
assess
temperatures
actually
experienced
in
the
field
is
poor
and
not
well
represented
by
mean
reach
temperature.
Jensen
(
1990)
noted
t
hat
in
two
streams
growth
was
best
predict
ed
by
using
the
75%
temperature
(
the
median
between
the
mean
and
maximum),
whereas
for
another
stream
growth
was
best
predicted
using
mean
temperature.
Assuming
that
Jensen
could
measure
the
actual
diel
cycle
experienced
by
brown
trout
in
these
streams,
the
similar
ability
of
the
75%
temperature
in
predicting
growth
and
in
estimating
equivalent
acclimation
temperatures
in
UILT
tests
is
interesting.
It
appears
that
physiological
conditioning
of
fish
in
fluctuating
temperatures
adjusts
their
growth
and
thermal
tolerance
toward
levels
that
would
be
predicted
under
constant
temperatures
located
between
the
mean
and
the
maximum.

Another
possible
explanation
no
t
given
by
Jensen
(
1990)
for
greater
growth
rates
in
the
field
is
that
food
quality
in
the
field
is
better
than
that
provided
in
laboratory
experiments.
Also,
fat
content
of
macroinvertebrates
in
the
drift
could
be
higher
than
the
average
of
prey
available
in
the
benthos
and
provide
a
high­
calorie
diet.
Food
quantity,
however,
is
often
considered
limiting
to
fish
growth
in
the
field
(
Brett
et
al.
1982).
Growth
rates
of
wild
rainbow
trout
in
the
field
have
generally
been
reported
as
<
1%/
d
(
see
review
by
Wurtsbaugh
and
Davis
1977),
but
were
higher
than
this
in
the
laboratory
in
every
season
under
the
natural
temperature
regime
(
mean
seasonal
temperatures
in
the
laboratory
of
50,
44.4,
48.9,
48.9
and
61.1
°
F
[
10,
6.9,
9.4,
and
16.2
°
C]
in
autumn,
winter,
spring,
and
summer,
respectively)
when
fish
were
fed
to
satiation.

Other
studies
have
noted
that
mean
temperatures
are
useful
in
predicting
growth
rates.
Growth
rates
of
sockeye
fry
(
Babine
Lake,
BC,
stock)
were
measured
at
satiation
feeding
(
3
51
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
times/
d)
from
March
to
mid­
May
under
three
temperature
regimes:
constant
50
°
F
(
10
°
C),
declining
23.4
to
12.6
°
F
(
13
to
7
°
C),
and
increasing
12.6­
23.4
°
F
(
7
to
13
°
C).
Mean
temperature
was
50
°
F
(
10
°
C)
in
each
treatment.
Rate
of
temperature
change
in
the
declining
or
increasing
treatments
was
1.8
°
F
(
1
°
C)/
wk
over
a
56­
d
period.
Although
mean
temperature
can
be
a
suitable
index
to
growth
rate
under
a
fluctuating
temperature
regime,
the
studies
above
did
not
subject
fish
to
either
extreme
temperature
maxima
or
extreme
diel
fluctuations.

Has
acclimation
to
a
temperature
higher
than
the
mean
of
a
diel
cycle
been
demonstrated?

In
addition
to
the
research
discussed
above,
Clarke
(
1978)
measured
growth
rates
of
juvenile
sockeye
in
the
laboratory
at
constant
and
fluctuating
temperatures.
At
constant
temperatures
ranging
from
45.5
to
63.5
°
F
(
7.5­
17.5
°
C),
growth
rates
increased
linearly.
This
response
was
defined
by
the
equation
y
=
0.0660x
!
0.311,
where
x
is
mean
temperature
and
y
is
growth
rate
(%
wt/
d).
At
45.5
°
F
(
7.5
°
C),
growth
rate
was
approximately
0.2%/
d
and
at
63.5
°
F
(
17.5
°
C)
it
was
approximately
0.8%/
d.
At
a
constant
50
°
F
(
10
°
C)
regime,
growth
rate
was
0.35%/
d
(
estimated
by
regression
for
all
constant
temperature
growth
experiments),
but
under
fluctuating
regimes
of
44.6­
55.4
°
F
(
7­
13
°
C)
and
41­
59
°
F
(
5­
15
°
C)
(
mean
daily
temperatures
of
50
°
F
[
10
°
C]),
growth
rates
were
about
0.47%/
d
and
0.63%/
d,
respectively.
This
study
indicated
that
specific
growth
rate
(
as
%
wt/
d)
at
44.6­
55.4
°
F
(
7­
13
°
C)
was
equivalent
to
that
observed
at
a
constant
temperature
of
52.5
°
F
(
11.4
°
C).
Under
the
diel
regime
with
great
amplitude
(
41­
59
°
F
[
5­
15
°
C]),
growth
was
equivalent
to
that
observed
at
a
constant
temperature
of
57
°
F
(
13.9
°
C).
This
indicates
that
under
diel
fluctuating
regimes,
there
was
an
acclimation
to
an
equivalent
temperature
between
the
mean
and
the
maximum
temperature.
In
terms
of
growth
rates,
t
his
acclimation
effect
was
similar
to
that
observed
in
survival
under
thermal
stress
with
prior
acclimation
in
cyclic
diel
temperature
regimes.

Are
there
seasonal
differences
in
growth
rates
not
related
to
temperature?

Jensen
(
1990)
noted
that
a
decreasing
autumn
temperature
trend
caused
growth
to
be
less
at
a
given
temperature
than
at
the
same
temperature
under
a
generally
increasing
temperature
trend
in
spring.
Such
a
seasonal
effect
has
been
observed
in
brown
trout
and
Atlantic
salmon
by
some
authors,
but
others
have
not
detected
any
seasonal
difference
at
comparable
temperatures
(
Jensen
1990).
A
study
by
Mortensen
(
1985
as
cited
by
Jensen
1990)
indicated
that
0+
and
1+
brown
trout
gro
wth
rate
in
the
field
during
spring
was
accurately
predicted
using
Elliott's
model,
but
growth
rate
was
only
60%­
90%
of
predicted
rates
in
summer
and
0%­
30%
in
winter.
Jensen
attributed
the
realized
growth
rate
to
seasonal
limitation
in
food
availability.

What
research
seems
to
best
describe
the
influence
of
fluctuating
temperature
on
growth?

Probably
the
best
study
of
the
effect
of
fluctuating
temperature
on
salmonids
is
that
of
Hokanson
et
al.
(
1977).
It
is
especially
useful
as
a
central
point
for
evaluating
other
studies
because
of
the
range
of
temperatures
evaluated,
the
fact
that
both
growth
and
survival
were
evaluated,
and
its
consistency
with
the
vast
literature
on
thermal
effects.
52
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
Hokanson
and
colleagues
studied
growth
and
survival
of
rainbow
trout
(
O.
mykiss)
juveniles
reared
on
maximum
rations
under
fluctuating
temperatures
(
T
°
F
±
6.8
°
F
[
3.8
°
C])
versus
constant
temperatures.
The
physiological
optimum
(
PO)
temperature
of
rainbow
trout
is
60.8­
64.4
°
F
(
16­
18
°
C).
These
authors
noted
that
specific
growth
rate
at
mean
temperatures
less
than
PO
was
lower
for
a
given
mean
temperature
under
a
co
nstant
(
T
°
F)
versus
a
fluctuating
(
T
°
F
±
6.8
°
F
[
3.8
°
C])
temperature
regime.
This
indicates
a
benefit
of
a
fluctuating
regime
when
the
mean
temperature
is
less
than
PO.
In
this
temperature
zone,
a
constant
temperature
of
T+
2.2
°
F
(
1.5
°
C)
provided
comparable
specific
growth
rate
to
juveniles
reared
at
T
°
F
±
6.8
°
F
(
3.8
°
C).
In
other
words,
we
would
have
to
increase
an
initial
constant
temperature
by
2.7
°
F
(
1.5
°
C)
to
provide
growth
rates
equivalent
to
t
hose
exhibited
under
a
fluctuating
regime
having
a
mean
equal
to
the
initial
constant
temperature.
However,
specific
growth
rates
at
mean
temperatures
greater
than
PO
were
higher
at
constant
than
fluctuating
temperatures
having
the
same
mean
temperature.
This
indicates
that
when
water
temperature
under
field
conditions
is
greater
than
PO,
it
is
not
safe
to
assume
that
a
fluctuating
regime
is
protective
on
the
basis
of
its
mean,
even
if
the
mean
itself
is
not
injurious
under
constant
temperature
experiment
s.
The
negative
influence
of
the
diel
cycle
appears
to
come
from
exposure
to
temperatures
higher
than
the
mean
when
the
mean
is
greater
than
PO.

This
pattern
led
Hokanson
and
colleagues
to
suggest
that
the
growth
of
rainbow
trout
appears
to
be
accelerated
under
fluctuating
temperatures
when
the
mean
temperature
is
below
the
constant
temperature
optimum
for
growth
and
retarded
by
fluctuating
temperatures
when
the
mean
is
higher.
Hokanson
et
al.
suggested
that
water
quality
standards
(
based
on
weekly
mean
values)
should
be
set
such
that
the
average
weekly
temperature
is
below
the
constant
test
temperature
producing
maximum
growth.
They
determined
that
rainbow
trout
growth
rates
under
fluctuating
regimes
do
not
correspond
to
those
in
a
constant
temperature
regime
having
a
mean
equal
to
that
for
the
cycle.
Rat
her,
they
acclimate
to
some
value
between
the
mean
and
maximum
daily
temperatures
and
consequently
their
growth
rates
reflect
this
"
effective"
temperature.
Looked
at
ano
ther
way,
the
optimal
fluctuating
regime
had
a
mean
of
59.9
°
F
(
15.5
°
C)
with
a
range
of
53­
66.7
°
F
(
11.7­
19.3
°
C),
and
the
optimal
constant
test
temperature
of
63
°
F
(
17.2
°
C)
fell
approximately
midway
between
the
daily
mean
and
the
daily
maximum
of
the
optimal
fluctuating
test.

Most
of
the
research
on
o
ptimal
growth
temperatures
is
conducted
at
a
const
ant
temperature.
Water
quality
standards,
however,
must
apply
to
naturally
fluctuating
thermal
environments.
Because
temperature
directly
affects
the
metabolism
of
fish,
a
fish
kept
continuously
in
warm
water
will
experience
more
metabolic
enhancement
than
one
that
experiences
the
same
temperature
for
only
1
or
2
hours
per
day.
Thus,
constant
test
results
cannot
be
reasonably
applied
directly
to
the
daily
maximum
temperature
in
a
fluctuating
stream
environment.
Although
the
constant
temperature
test
results
could
be
used
to
represent
daily
mean
temperatures,
it
is
believed
that
the
daily
maximum
temperature
is
more
influential
to
the
biology
and
should
be
the
focus
of
any
standards
developed.

Clarke
(
1978)
studied
individual
specific
growth
rates
of
underyearling
sockeye
salmon
after
42
d
at
five
constant
temperatures
ranging
from
45.5
to
63.5
°
F
(
7.5­
7.5
°
C)
and
two
diel
cycles
of
44.6­
55.4
°
F
(
7­
13
°
C)
and
41­
59
°
F
(
5­
15
°
C).
At
constant
temperature,
there
was
a
linear
increase
in
growth
rate
over
the
range
45.5­
63.5
°
F
(
7.5­
17.5
°
C).
Bot
h
thermocycles
had
a
mean
of
50
°
F
53
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
(
10
°
C),
but
growth
was
greater
on
the
41­
59
°
F
(
5­
15
°
C)
cycle.
The
author
notes
that
the
equivalent
constant
temperature
for
specific
growth
rate
in
length
on
the
44.6­
55.4
°
F
(
7­
13
°
C)
cycle
was
increased
significantly
from
50
°
F
(
10
°
C)
in
o
ne
replicate
(
54.1
°
F
[
12.3
°
C])
but
no
t
in
the
other
(
51.4
°
F
[
10.8
°
C]).
Specific
growth
rate
in
length
on
the
41­
59
°
F
(
5­
15
°
C)
cycle
was
equivalent
to
t
hat
on
a
const
ant
temperature
of
59.5
°
F
(
15.3
°
C).
Specific
growth
rate
in
weight
on
the
44.6­
55.4
°
F
(
7­
13
°
C)
cycle
was
equivalent
to
that
on
a
constant
52.5
°
F
(
11.4
°
C);
on
the
41­
59
°
F
(
5­
15
°
C)
cycle
it
was
the
equivalent
of
a
constant
57
°
F
(
13.9
°
C).
This
study
concludes
that
underyearling
sockeye
salmon
exposed
to
diel
thermocycles
are
able
to
acclimate
their
growth
rates
to
a
temperature
above
the
mean
of
the
cycle.

Dickerson
et
al.
(
1999
and
unpublished
data,
as
cited
in
Dunham
1999)
conducted
experiments
with
hatchery­
reared
Pyramid
Lake
strain
Lahontan
cutthroat
trout.
Fish
were
exposed
to
1
wk
fluctuating
temperatures
(
68­
78.8
°
F
[
20­
26
°
C];
mean
=
73.4
°
F
[
23
°
C])
and
to
constant
temperatures
of
55.4,
68,
and
73.4
°
F
(
13,
20,
and
23
°
C).
Growth
rates
in
the
fluctuating
temperature
tests
were
lower
than
for
fish
exposed
to
constant
temperatures
of
55.4
and
68
°
F
(
13
and
20
°
C),
but
were
similar
to
groups
of
fish
held
at
a
constant
73.4
°
F
(
23
°
C).

Hahn
(
1977)
invest
igated
the
effect
s
of
fluctuating
(
46.4­
66.2
°
F
[
8­
19
°
C])
and
constant
(
47.3,
56.3,
65.3
°
F
[
8.5,
13.5,
18.5
°
C])
temperatures
on
steelhead
trout
fry
and
yearlings.
He
found
that
as
many
fish
remained
in
the
fluctuating
regime
as
in
the
constant
56.3
°
F
(
13.5
°
C)
temperature
water;
twice
as
many
remained
in
the
fluctuating
temperature
regime
as
remained
in
the
constant
65.3
°
F
(
18.5
°
C)
temperatures;
and
twice
as
many
fish
remained
in
constant
47.3
°
F
(
8.5
°
C)
water
as
in
the
fluctuating
temperature
regime.
By
inference,
Hahn
found
the
relationship
among
the
three
constant
temperatures
was
the
same
as
the
relationship
of
each
to
the
fluctuating
temperature:
twice
as
many
fish
in
56.3
°
F
(
13.5
°
C)
as
in
65.3
°
F
(
18.5
°
C),
twice
as
many
fish
in
47.3
°
F
(
8.5
°
C)
as
in
56.3
°
F
(
13.5
°
C),
and
four
times
as
many
fish
in
47.3
°
F
(
8.5
°
C)
as
in
65.3
°
F
(
18.5
°
C).
We
can
conclude
from
Hahn's
work
that
juveniles
had
equal
preference
for
constant
(
56.3
°
F
[
13.5
°
C])
water
and
fluctuat
ing
(
46.4­
66.2
°
F
[
8­
19
°
C])
water
with
a
mean
of
56.3
°
F
(
13.5
°
C).
Although
not
a
growth
t
est,
the
Hahn
study
supports
t
he
general
premise
t
hat
daily
mean
temperatures
are
reasonable
approximations
of
constant
exposure
test
temperatures.

Grabowski
(
1973)
conducted
growth
experiments
with
steelhead
trout.
Fish
were
fed
a
percentage
of
body
weight
according
to
feeding
charts
twice
per
day
based
on
temperature
and
changes
in
body
weight.
To
evaluate
growth,
fish
were
subjected
to
four
test
temperatures
for
8
wk.
These
four
regimes
were
a
fluctuat
ing
test
from
46.4
to
64.4
°
F
(
8­
18
°
C)
(
mean
55.4
°
F
[
13
°
C])
and
constant
tests
held
at
46.4,
59,
and
64.4
°
F
(
8,
15,
and
18
°
C).
Steelhead
grew
better
at
59
°
F
(
15
°
C)
than
at
ot
her
temperatures.
Fish
in
the
fluctuating
test
had
the
second
highest
growth
rate
and
actual
weight
gain.
Growth
rate
in
the
fluctuating
test
was
only
13%
less
than
that
at
the
constant
test
of
59
°
F
(
15
°
C),
while
growth
rates
at
46.4
and
64.4
°
F
(
8
and
18
°
C)
were
47%
and
21%
less,
respectively.
Plotting
the
data
using
the
midpoint
in
the
fluctuating
test
as
a
surrogate
for
a
constant
test
condition
creates
near
linear
growth
from
46.4
to
59
°
F
(
8­
15
°
C),
with
a
steep
drop
as
temperature
progresses
to
64.4
°
F
(
18
°
C).
Thus
the
mean
of
the
fluctuat
ing
treatment
appears
generally
comparable
to
a
constant
test
temperature
of
the
same
value.

Thomas
et
al.
(
1986)
investigated
the
effects
of
diel
temperature
cycles
on
coho
salmon.
Temperature
cycles
(
50­
55.4,
48.2­
59,
46.4­
62.6,
and
43.7­
68
°
F
[
10­
13,
9­
15,
8­
17,
and
54
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
6.5­
20
°
C])
were
used
to
simulate
observed
temperatures
in
clearcuts
of
southeastern
Alaska.
Different
levels
of
feeding,
including
starvation,
were
used
in
each
of
the
tests.
Cyclic
temperatures
for
40
d,
averaging
51.8
°
F
(
11
°
C)
daily,
did
not
influence
growth
of
age­
0
fish
on
any
ration
in
comparison
to
t
he
controls
(
kept
at
a
constant
51.8
°
F
[
11
°
C]).
Plasma
cortisol
and
glucose
concentrations
were
significantly
greater
in
fish
maintained
for
20
d
in
the
43.7­
68
°
F
(
6.5­
20
°
C)
cycle,
which
may
be
an
indicator
of
long­
term
stress.
Thus,
in
the
work
by
Thomas
et
al.
(
1986)
the
daily
mean
of
the
fluctuating
test
and
the
constant
test
exposures
produced
essentially
equivalent
results,
but
stress
conditions
were
noted
to
o
ccur
in
cycles
with
daily
peak
temperatures
of
68
°
F
(
20
°
C).

Everson
(
1973)
used
the
data
of
Averett
(
1969)
to
show
that
growth
rates
and
gross
efficiencies
of
food
conversion
of
fish
kept
at
moderate
constant
temperatures
(
59.9
°
F
[
15.5
°
C])
were
somewhat
greater
than
those
of
fish
exposed
to
temperatures
that
fluctuated
about
a
similar
mean
value
(
60
°
F
[
15.6
°
C]),
whereas
at
higher
average
temperatures
the
fluctuation
of
temperature
markedly
benefited
the
growth
and
food
conversion
efficiency
of
the
fish.
Thus
Everson
showed
support
for
the
assumption
that
fluctuating
temperatures
can
produce
greater
benefits
to
growth
than
can
higher
constant
temperatures.

What
is
the
range
of
laboratory
growth
rates
under
fluctuating
temperature
vs.
constant
temperature?

There
appears
to
be
considerable
controversy
regarding
the
effect
o
f
fluctuating
temperatures
vs.
constant
temperatures
on
juvenile
growth
rate.
Peterson
and
Martin­
Robichaud
(
1989)
studied
growth
of
Atlantic
salmon
under
daily
temperature
cycles
of
53.6­
68
°
F
(
12­
20
°
C)
and
60.8­
68
°
F
(
16­
20
°
C)
relative
to
constant
temperatures
of
60.8
and
68
°
F
(
16
and
20
°
C)
and
could
find
no
differences.

Thomas
et
al.
(
1986)
measured
growth
of
juvenile
coho
for
40­
d
periods
under
constant
51.8
°
F
(
11
°
C)
temperature
vs.
diel
temperature
cycles
of
50,
55.4,
48.2,
59,
46.4,
62.6,
and
43.7­
68
°
F
(
10­
13,
9­
15,
8­
17,
and
6.5­
20
°
C),
all
of
which
averaged
51.8
°
F
(
11
°
C).
They
found
that
the
growth
rates
of
0+
age
fish
at
any
of
the
food
rations
were
not
significantly
different
among
temperature
regimes,
although
the
growth
at
4%
and
8%
ration
(
i.
e.,
8%
of
body
weight/
day)
was
better
than
at
1%.

Konstantinov
et
al.
(
1989)
reported
that
under
fluctuat
ing
thermal
regimes
coho
salmon
have
a
decreased
respiration
rate
and
increased
growth
rate
relative
to
that
at
constant
temperatures.
This
coupling
o
f
respiration
and
growth
causes
greater
efficiency
in
use
of
assimilated
energy
in
growth.
Konstantinov
and
Zdanovich
(
1986
as
cited
by
Behnke
1992)
measured
greater
growth
rates
in
several
fish
species
under
fluctuating
vs.
constant
temperature
regimes.
Konstantinov
et
al.
(
1989),
summarizing
several
of
their
studies
on
effect
of
fluctuating
thermal
regimes
on
fish,
stated
that
growth
rate
under
a
fluctuating
regime
tends
to
be
10%­
40%
greater
than
at
constant
temperatures
equal
to
the
mean
of
the
cycle.

Biette
and
Geen
(
1980)
reported
variable
response
of
0+
age
sockeye
to
cyclic
temperature
regimes
relative
to
constant
temperatures
depending
on
food
ration.
Under
zooplankton
rat
ions
equal
to
4.0%­
6.9%
dry
body
weight/
d
and
a
fluctuating
temperature
similar
to
that
experienced
55
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
in
the
field
in
diel
migrations,
sockeye
grew
as
well
or
more
rapidly
than
under
constant
temperatures
of
60.6,
59.5,
52.3,
or
43.1
°
F
(
15.9,
15.3,
11.3,
or
6.2
°
C).
This
ration
was
estimated
to
be
comparable
to
that
consumed
under
field
conditions
in
Babine
Lake.
Rearing
sockeye
underwent
diel
vertical
migrations
between
the
hypolimnion,
having
temperatures
of
41­
48.2
°
F
(
5­
9
°
C),
and
the
epilimnion,
with
53.6­
64.4
°
F
(
12­
18
°
C)
water.
During
periods
of
maximum
lake
temperature,
sockeye
inhabited
the
epilimnion
for
2
h
in
early
afternoon
and
2
h
in
early
evening.
At
higher
food
rations,
growth
at
constant
high
or
intermediate
temperatures
exceeded
that
under
cyclic
temperatures.
At
both
high
and
low
rations,
food
conversion
efficiency
and
growth
were
greater
in
a
constant
temperature
regime
than
under
fluctuat
ing
conditions
during
daily
vertical
migrations
in
the
field.

Wurtsbaugh
and
Davis
(
1977)
studied
growth
of
steelhead
trout
in
laboratory
streams
under
three
fluctuating
temperature
regimes
(
natural
cycle,
natural
+
5.4
°
F
[
3
°
C],
and
nat
ural
+
10.8
°
F
[
6
°
C])
in
all
four
seasons
and
found
that
trout
growth
could
be
enhanced
by
temperature
increases
up
to
29.7
°
F
(
16.5
°
C).
During
the
summer
season
the
control
temperature
(
natural
cycle)
was
61.1
°
F
(
16.2
°
C)
(
mean)
and
the
elevated
temperatures
averaged
67.1
and
72.5
°
F
(
19.5
and
22.5
°
C).
The
average
diel
temperature
range
for
the
summer
growth
period
was
about
6.1
°
F
(
3.4
°
C)
under
the
three
treatments.
Growth
rates
under
food
consumption
rates
of
5%­
15%
dry
body
wt/
d
were
higher
under
the
control
temperature
regime
than
at
the
elevated
fluctuating
regimes.
Under
the
high
temperature
regime
(
mean
of
72.5
°
F
[
22.5
°
C])
growth
rate
was
zero
at
a
food
consumption
rate
of
7%/
d.
Gross
food
conversion
efficiency
decreased
as
temperatures
increased
from
61.1
to
72.5
°
F
(
16.2­
22.5
°
C).
Maintenance
rations
increased
by
a
factor
of
three
over
the
temperature
range
44.4­
72.5
°
F
(
6.9­
22.5
°
C).
This
study
revealed
that
trout
growth
was
improved
by
increasing
temperatures
up
to
a
maximum
of
61.7
°
F
(
16.5
°
C),
but
that
this
threshold
applies
to
the
field
only
under
satiation
feeding.
Because
researchers
measured
field
growth
rates
in
an
Oregon
coastal
stream
indicating
food
limitation,
they
concluded
that
temperatures
less
than
61.7
°
F
(
16.5
°
C)
would
be
optimal
for
the
trout.
Food
limitations
in
trout
streams
not
uncommonly
cause
great
reductions
in
summer
growth
(
Cada
et
al.
1987).

Laboratory
growth
experiments
were
run
on
juvenile
rainbow
trout
reared
in
Lake
Ontario
water
(
Dockray
et
al.
1996).
Growth
was
measured
for
juveniles
over
a
90­
d
period
in
which
"
control"
temperatures
followed
the
ambient
lake
diel
fluctuations
and
also
varied
in
daily
mean
temperature
from
55.4
to
75.2
°
F
(
13­
24
°
C)
over
this
summer
period.
A
water
treatment
facility
resulted
in
increasing
control
temperatures
by
3.6
°
F
(
2
°
C)
over
background
for
each
day
of
the
growth
study.
Growth
rate
over
this
period
was
significantly
less
for
the
warmer
regime,
having
mean
daily
temperatures
of
59­
78.8
°
F
(
15­
26
°
C).
A
comparison
of
the
day
0­
30
initial
growth
period
with
the
day
60­
90
growth
period
is
revealing.
The
initial
period
had
daily
control
temperatures
varying
from
55.4
to
64.4
°
F
(
13­
18
°
C);
the
final
period
had
temperature
variation
from
66.2
to
75.2
°
F
(
19­
24
°
C).
The
treatment
temperature
regime
was
equal
to
the
daily
control
temperatures
+
3.6
°
F
(
2
°
C).
In
the
first
30­
d
period,
food
conversion
efficiencies
were
42.4%
and
45.6%,
respectively,
for
the
control
and
treatment
fish.
For
the
final
30­
d
period,
conversion
efficiencies
were
27.3%
and
6.2%,
respectively.
The
warmer
temperature
regimes
in
the
final
30­
d
period
substantially
reduced
conversion
efficiency
from
the
initial
period.
This
effect
was
very
pronounced
in
the
69.8­
78.8
°
F
(
21­
26
°
C)
regime
for
treatment
fish
in
the
final
30­
d
growth
period.
In
addition,
growth
was
just
barely
positive
for
the
last
30­
d
growth
period
for
fish
in
the
69.8­
78.8
°
F
(
21­
26
°
C)
regime.
56
Summary
of
Technical
Literature
Examining
the
Physiological
Effects
of
Temperature
Troughs
stocked
at
high
density
with
rainbow
trout
were
supplied
with
Columbia
River
water
in
test
s
of
growth
rate
and
disease
susceptibility
(
Fujihara
et
al.
1971).
Water
in
troughs
was
maintained
at
ambient
conditions
for
July
(
63.8­
71
°
F,
mean
67.4
°
F
[
17.7­
21.7
°
C,
mean
19.7
°
C]),
ambient!
4
°
F
(
2.2
°
C),
and
ambient+
4
°
F
(
2.2
°
C).
Growth
rate
under
the
reduced
temperature
was
44%
greater
than
under
the
ambient
condition,
even
though
mortality
rates
associated
with
columnaris
disease
were
comparable.

In
anot
her
study
on
O.
mykiss
(
st
eelhead
parr
from
Dworshak
National
Fish
Hatchery,
Idaho),
growth
rate
under
a
fluctuating
temperature
with
feeding
2
times/
d
to
satiation
was
contrasted
with
growth
at
constant
temperatures
of
46.4,
59,
and
64.4
°
F
(
8,
15,
and
18
°
C)
for
2­
and
8­
wk
periods.
Best
steelhead
growth
occurred
at
59
°
F
(
15
°
C).
By
contrast,
instantaneous
growth
rate
under
t
he
fluctuating
temperature
was
11%
less
(
Grabowski
1973).
The
thermocycle
was
sinusoidal,
so
a
mean
temperature
of
55.4
°
F
(
13
°
C)
can
be
inferred.
Growth
at
constant
temperatures
of
46.4
and
64.4
°
F
(
8
and
18
°
C)
was
36%
and
29%
less
than
at
59
°
F
(
15
°
C)
(
Grabowski
1973).
These
data
allow
one
to
hypothesize
that
the
effective
growth
temperature
for
the
46.4­
64.4
°
F
(
8­
18
°
C)
cycle
was
close
to
59
°
F
(
15
°
C),
but
it
is
not
possible
to
determine
whether
it
was
slightly
above
or
below
59
°
F
(
15
°
C).

In
summary,
laboratory
studies
indicate
that
increasing
food
rations
between
1%
and
8%
body
weight/
d
results
in
an
increased
growth
rate
(
Thomas
et
al.
1986,
Elliott
1994).
Growth
rates
have
been
found
to
be
no
different
under
fluctuating
than
under
constant
temperature
equal
to
the
mean
of
the
cycle
(
Peterson
and
Martin­
Robichaud
1989,
Thomas
et
al.
1986).
In
contrast,
growth
rates
under
fluctuating
regimes
have
been
reported
as
greater
than
at
constant
temperatures
equal
to
the
mean
of
the
cycle
(
Konstantinov
et
al.
1989,
Konst
antinov
and
Zdanovich
1986,
Clarke
1978,
Biette
and
Geen
1980).
The
study
by
Biette
and
Geen
(
1980)
indicates
that
a
fluctuating
temperature
regime
might
confer
a
growth
advantage
on
juvenile
sockeye
under
low,
rather
than
high,
food
availability
as
typically
found
in
lake
environments.
Enhanced
growth
under
a
fluctuating
temperature
regime
might
reflect
an
acclimation
to
a
temperature
higher
than
the
mean
of
the
cycle,
similar
to
responses
exhibited
in
tests
of
lethal
temperatures
in
survival
studies.

Other
studies
have
reported
that
fluctuating
temperature
regimes
are
not
all
equal.
For
example,
under
three
fluctuating
regimes
in
which
diel
temperature
varied
approximately
6.1
°
F
(
3.4
°
C)
in
each,
steelhead
growth
rate
was
greatest
in
the
fluctuating
regime
with
the
lowest
mean
(
61.7
°
F
[
16.5
°
C])
as
opposed
to
those
with
means
of
67.1
and
72.5
°
F
(
19.5
and
22.5
°
C)
(
Wurtsbaugh
and
Davis
1977).
A
very
similar
result
was
obtained
with
rainbow
trout
(
Fujihara
et
al.
1971),
in
which
the
highest
growth
rate
occurred
at
the
lowest
mean
temperature
(
63.5
°
F
[
17.5
°
C])
in
a
fluctuating
regime.
In
another
study
with
steelhead,
highest
growth
rate
occurred
at
59
°
F
(
15
°
C)
under
constant
temperatures
(
Grabowski
1973).
In
this
study
a
fluctuating
regime
(
46.4­
64.4
°
F
[
8­
18
°
C])
with
a
mean
of
55.4
°
F
(
13
°
C)
had
a
growth
rate
less
than
that
at
59
°
F
(
15
°
C).
Studies
that
indicate
a
reduction
of
growth
rate
under
fluctuating
temperatures
occurs
when
fluctuations
extend
above
the
zone
of
best
constant
temperature
growth
(
approx.
55.4­
60.8
°
F
[
13­
16
°
C])
for
salmonids
under
satiation
feeding.
Fluctuating
temperatures
appear
to
provide
a
growth
benefit
to
salmonids
when
the
mean
of
the
cycle
is
lower
than
the
const
ant
temperature
growth
optimum.
In
this
manner
all
the
studies
cited
above
are
consistent
with
findings
of
Hokanson
et
al.
(
1977).