SUMMARY
95
1. The experimental fish, Tilapia mossambica .were collected from local
fish farm
and adapted to
laboratory conditions and maintained at
normal room temperature (25°C _+ 0.5°C).
2. For all experimental purposes, one batch of fish from lab temperature
was adapted to 20°C (and another batch of fish was adapted to 30°C/
through the estimation of oxygen consumption daily, till
a constant
value.
it reached
For
adaptation to
lower
temperature (20°C),
a
12-day sojourn and for
adaptation to
higher
temperature (30°C),
a
10-day sourn were allowed.
3. In order to differentiate and distinguish temperature-stress phenomenon
from temperature-adaptation process, one batch of fish from 20°C adapted
fishes was readapted
i) to a slow rise of ambient temperature from 20°C to 30°C
at the rate of l°C/2 days, and
ii)
<
the
other
batch
of fishwas subjected to
an abrupt
temperatutrechange from 20°C to 30°C at the rate of l°C/hr.
Thus, the experimental fishes are grouped under two categories f namely (
i) temperature-adapted fishes ii) temperature-stressed fishes.
k. The rate of
oxygen consumption
and
opercular
activity
were found
to be higher in 30°C adapted fishes, when compared to 20°C adapted
fishes, indicating greater energy demands of the fish during adaptation
to higher temperature.
In the case of
Tilapia mossambica which are
subjected to a slow temperature change from 20°C to 30°C at the
96
rate of
i°C/2 days,
the tiroe-course experiments with reference
to basic physiological parameters 1 ike/ oxygen consumption of whole
fish and opercular activity reveal
that^there is a gradual stepping
up of these two parameters ; and ultimately, reached the control
values (30°C adpated fishes) within 30 days of exposure as reflected
in the maximum percent increase, with a complete recovery in
these
parameters,
thus,
results
in
the
process
of
temperature-
adaptation without
physiological
load on the part of the fish.
On the otherhand,
in the case of fishes exposed abruptly to a
temperature change ( from 20°C to
30°C at the rate of
l°C/hr,
there is no stepping up of oxygen consumption and opercular activity
and the values in these parameters could not reach the control
values even over a period of 30 days.
Further, in stress situation,
these two factors fluctuate considerably in their levels over longer
period and continued stress acting upon the fish culminates ultimately
in the situation of
"stress-adaptation"
increase and percent recovery
with
a far
less percent
in these parameters during stress.
Obviously, this is due to the physiological load acting upon this
stressed
fish.
Thus,
temperature-adaptation
is
different
from
temperature-stress.
5.
The 30°C adapted fishes registered relatively higher rate of heart
beat and RBC number as against the 20°C adapted fishes.
haematological
parameters,
such
as the rate of
In the
heart beat and
RBC number, the temperature-adapted fishes exhibited a gradual
97
elevation
in
both
these
parameters
between the two factors.
with
a
linear
relationship
And further, these parameters reached
the control values with a relatively higher percent increase and
complete percent recovery
the
contrary,
RBC
these
in licart beat rat&and RBC count.
haematological
parameters,
count exhibited in a different way
On
heart beat rate and
in that they fluctuate
to a greater extent in initial periods of stress situation followed
by a greater decline in their levels especially with the operation
of bradycardia (slowing of heart beat) which is observed in stressed
fishes^nd it is an indicator of stress situation in Tilapia mossambica.
Unlike
recovery
in
the
adapted
fishes, the
percent
in heart beat and RBC number
increase
and percent
are relatively brought
down to a much lower level by dint of undue burden on the part
of the fish,
probably, with a rapid or steady release of energy
during stress-condition.
6.
There is a precise inverse relationship between the blood glucose
and liver glycogen during adaptation
to higher temperature in Tilapia
mossambica with the operation of glycogenolysis.
During adaptation
of
a steep
this
fish
to higher temperatures,
there
is
increase
in the blood glucose with a concomitant decrease in liver glycogen,
suggesting that blood glucose is derived from hepatic glycogenolysis
to meet
the higher
energy
demands during thermal
adaptations.
The reaching of the control was observed in these two parameters
in temperature-adapted fishes with a maximum increase of
156%
98
in
blood
glucose
glycogen.
and
Further,
amount of recovery
maximum
the
adapted
percent
decrease
64%
fishes exhibited a
in
liver
fairly good
ie., 95% in blood glucose and 93% in liver
glycogen, as against this, the temperature-stressed fishes could not
show any indications of the reaching of the controls nor exhibited
complete recovery in these parameters.
the
normal
impaired.
operation
of
carbohydrate
In these stressed fishes,
metabolism
seems
to
be
Hence,the stressed fish could not bring about the process
of hepatic glycogenolysis to the maximum extent for the release
of energy.
inhibited
And continuous stress acting upon Ti lapia mossambica
carbohydrate
metabolism
and
ultimately
resulted
in
the operation of stress-adaptation.
7.
The results of the AchE activity and Adi content in this fish have
shown
that
the
enhancement
a corresponding decrease
like
gill,
intestine
in kidney and liver
of
AchE
activity
in the Ach content
was followed by
in all
the tissues
brain, red muscle and white muscle, except
which showed a reverse trend.
Acetylcholineste­
rase activity is maximum in the brain among the different organs
in
Tilapia mossambica.
This
indicates the
integrating role of
the central nervous system during the adaptation.
AchE activity
is very low in the liver and kidney of Tilapia mossambica, suggesting
that AchE activity has very little to do with the cellular metabolism
In
the temperature-adapted
up
of
AchE
fishes,
there
is
a
gradual
activity with a concomitant gradual
of Ach content.
stepping
stepping down
And these parameters reached the controls (30°C
99
adapted fishes).
Further, the adapted fishes indicated full recovery
in AchE activity and Ach content in all the tissues with a maximum
percent increase (ranging from 133 to 200%) in AchE activity and
with
the
maximum
in Ach content,
percent
decrease
(ranging from
59
to
71%)
suggesting the efficient hydrolysis of Ach into
choline and acetic acid without the inactivation of AchE enzyme,
for the smooth function of the nerve-impulse during process of
temperature-adaptation.
The
percent
change
and
the
percent
recovery in AchE activity and Ach content which are found signi­
ficantly greater in the
order of brain > gill > red muscle > white
muscle y intestine ^ kidney >•
kidney
liver in AchE activity/ and, brain>
> liver >white muscle > red muscle > intestine > gill in
Ach content.
But in temperature-stressed fishes, these enzymatic
parameters did not reach the control values.
This might be due
to inactivation of the enzyme AchE during a sudden rise in tempera­
ture at the rate of l°C/hr and the percent change ie., the percent
increase in all the tissues ranging from 40 to 67% in AchE activity
and
13 to 24% decrease
in
Ach
content
during stress situation.
Brain is affected to the maximum when compared to other tissues
during temperature-stress situation.
Hence ^measurement of brain AchE
elevation in this fish could be taken as a diagnosis of thermal
pollution.
8.
In
Tilapia mpssambica adapted
to 30°C
when compared to 20°C
adapted ones, the energetically more efficient oxidative metabolism
(as measured by SDH activity)
is consistently higher in the gill,
100
kidney and intestine (osmoregulatory organs) than in the brain, liver,
red muscle and white muscle (non-osmoregulatory organs).
Perhaps,
energy demands are higher on adaptation to higher temperatures,
and also they are higher
the
non-osmoregulatory
of osmo-and
higher
in the osmoregulatory organs than in
organs.
iono - regulation
temperature.
SDH
This
during
activity
indicates
adaptation
represents
the importance
of
the
a good
fish
to
index
of
oxidative metabolism during temperature-adaptation and temperaturestress.
During temperature-adaptation
SDH
activity
stepped
up
gradually and attained the original control values in all the tissues.
The
percent
increase
in
SDH activity
varied from 94 to 213%
whereas the percent recovery in SDH activity was also very high
and ranged from 96% to 99% indicating almost complete recovery
during temperature adaptation.
stressed
values
On the otherhand, in temperature-
fishes f the SDH activity
as a result of
lower
levels of % increase in its activity from 19% to 100% only.
Thus,
the
(30°C
stressed
adapted
fishes
fishes).
did not return to the control
could
Probably,
not
recover
completely
as
indicated
in the low percent recovery rates which ranged from 51 to 67%
and the percent recovery in the SDH activity is greater in
the
following order; brain > red muscle > gill > kidney > liver >
white muscle >
no
impairment
during
intestine.
of
oxidative
temperature-adaptation.
These findings indicate that there is
metabolism
But ( the
at
mitochondrial
oxidative
level
metabolism
is impaired in stressed fishes and the operation of TC./\ cycle might
101
have been decreased at mitochondrial level.
Amongst the different
tissues, the predominantly aerobic tissues are affected to a greater
extent than the predominantly anaerobic tissues during temperaturestress phenomenon.
9.
In Tilapia mossambica when compared to 20°C adapted and 30°C
fishes,
the
LDH activity in non-osmoregulatory tissues is much
higher than
in the
predominantly
is
osmoregulatory tissues.
glycolytic
predominantly
in
oxidative
its metabolism,
in
its
White muscle is
whereas red muscle
metabolism,
as
reflected
in
its relatively greater LDH activity in white muscle than in the
red muscle.
In Tilapia mossambica f the energy demands in the
osmoregulatory organs during thermal adaptation are met by stepping
up
the
energetically
preference
to
more
the energetically
infact, is stepped down.
organs, energy
efficient
less
oxidative
metabolism
efficient glycolysis,
in
which
As against this, in the non-osmoregulatory
demands during thermal adaptation are met partly
by stepping up the energetically more efficient oxidative metabolism
and partly by steppingnpof energetically less efficient glycolysis.
It thus appears that( in Tilapia mossambica, the over all energetic
efficiency
is higher
in
the osmoregulatory organs (gill,
kidney
and intestine) than in the non-osmoregulatory organs (brain, liver,
red muscle and white muscle).
In fishes which are exposed very slowly to a temperature
change l°C/2 days, the LDH activity stepped up in the non-osmo-
102
regulatory tissues and stepped down in the osmoregulatory tissues,
gradually and ultimately returned to the control values of 30°C
adapted fishes, with much higher
levels of
percent increase
(135 to 147%) in non-osmoregulatory organs and (58 to 77%) percent
decrease
in osmoregulatory organs.
Further, these temperature
adapted fishes exhibited a very high degree of recovery in all
the tissues and it ranges from 94% to 99%.
With reference to
LDH activity, this percent recovery in LDH activity is greater
in the order of brain> red muscle> gill > white muscle > kidney > liver
;> intestine.
On the otherhand, the temperature-stressed fishes
could not show the reaching of the control values in the LDH
activity
in
all
the
tissues irrespective of osmoregulatory and
non-osmoregulatory in nature, and, further they could only decrease
or increase to a limited extent respectively (24 to 26% decrease;
10 to 28% increase).
activity
This low level of percent change in LDH
is also correspondingly reflected in the low level of
percent recovery in LDH activity also (32% to 54%).
This low level
of percent recovery in LDH activity during stress situation suggest
that pyruvate might not have been routed to TCA cycle in the
presence of physiological load acting upon the fish, and during
the conditions when aerobic oxidations are lowered.
Thus, there
appears to be the phenomenon of compensation and cooperativity
between oxidative and glycolytic metabolism in the tissues of
Tilapia
mossambica,
during stress situation.
reflecting
the
prevalence
of
anaerobiosis
103
10.
On the whole, these findings on the differentiation of "temperaturestress"
and "temperature-adaptation"
in this eury-thermal teleost^
Tilapia mossambica, clearly and precisely indicate that an abrupt
temperature
change
at
the
rate
of
l°C/hr,
within the normal
range of temperature from 20°C to 30°C acts as a stressor to
,
metabolism to the new temperature change.
Hence, stress is
Tilapia mossambica
and temporarily inhibits the adjustment of
a physiological load acting upon the animal and the factors causing
stress are termed as stressors, such as temperature of the present
study,
and continuous stress acting upon this fish resulted in
"stress-adaptation".
11.
On
the
otherhand,
a very slow temperature change, within the
normal range, from 20°C to 30°C at the rate of l°C/2 days, in
Tilapia mossambica, results in the process of adaptation, as a slow
process
of
of the fish.
compensation without physiological
load on the part
Thus, ’stress' is entirely different from 'adaptation'
and these two processes could be differentiated on the basis of
readaptation
experiments
as
shown
in
this
investigation,
with
due importance to the rate of thermal exposure.
12.
From these results on "temperature-adaptation" and "temperature-
f
when the fish are in the situation of stress, the normal mechanisms
stress'^ it appears as though in this teleost Tilapia mossambica,
of adaptation are switched off and the mechanisms concerned
with
Stress phenomenon are switched on and vice versa.
A high
104
degree of fluctuations by the Physiological and Biochemical para­
meters studied represent as good indicators of temperature-stress
in this fish.
13.
Thus, when poikilothermic animals subjected to any environmental
change, may be thermal, as it is in the present study, osmotic
or pollution and when the acclimation is complete, it was found
out from the present investigation that it is necessary and possible
and one has to differentiate the adaptation processes from other
phenomena
like
'stress-effects'
which
could
be easily
mistaken
for the adaptation processes coming across in the thermal regime
of the animal.
14.
Studies of this nature which could differentiate from environmental
stress
from environmental-adaptation with reference to ambient
temperature are highly useful
temperature
which
act
as
in the evaluation of the rates of
stressors
and
induce
stress
situation
on one hand, and , on the other in the evaluation of 'safe' and
'preferable'
rates of temperature which do not act as stressors,
but(result in the slow and easy compensation of adaptation, without
physiological
this
nature
load on the part of the animal.
are
highly
appreciable
in
Thus, studies of
evaluating
methods
and
techniques concerned with safe rearing and conservation of useful
fauna of the aquatic and terrestrial environments.