The study of the flow and transformation of energy in and between living organisms and their environment” Dr. K. Rama Rao Govt. Degree College TEKKALI; Srikakulam Dt. A. P Phone: 9010705687

2. The study of “the flow and
transformation of energy in and
between living organisms and
their environment”.
1. Energy Metabolism in Fish
2. Energy Sources,ces
3. Energy Requirements of Fish

3. 1. ENERGY METABOLISM IN FISH
Animals directly cannot utilize radiant
energy from the sun.
They get their needed energy from
oxidation of the complex molecules which
are eaten by the animal.
The energy is available until the complex
molecules are broken down to simpler
molecules by digestion.

4. The products of digestion are then
absorbed into the body of the animal
where oxidation processes occur
which release the energy.
Energy metabolism in fish is similar
to that in mammals and birds with
two notable exceptions. These
exceptions are:

5. (i) fish do not expend energy to
maintain a body temperature
different from that of their
environment; and
(ii) the excretion of waste nitrogen
requires less energy in fish than it
does in homeothermic land animals.

6. There are large differences in the
ability of different species of fish to
digest feed materials.
Fish species range all the way from
strict herbivores through omnivores
to carnivores.
The food requirements of different
species of fish vary greatly.

8. A. Energy Flow in Animals
The biological partition of energy in
fish, for maintenance and voluntary
activity must be satisfied before energy
is available for growth.
During times of low food intake fat and
protein are withdrawn from the animal
body to provide the energy needs for
maintenance and the animal loses
weight.

9. B. Energy Loss
Energy is lost from the body of a fish
in the faeces, urine, gill excretions
and as heat.
Also small amounts are lost from
external body surface.
The energy lost as heat comes from
three sources these are:

10. (a)Standard Metabolism (SM):
Which is the energy required to keep
the animal alive and is similar to
basal metabolism measured in
humans.
The difficulty of obtaining a
"motionless" animal, the definition
of basal metabolism is not
applicable to fish.

11. When a fish is motionless condition, it
struggles to free itself and uses more
energy than if allowed to swim freely in
still water.
SM is the minimum heat production of
an undisturbed fish in the "post
absorptive" state in still water.

12. (b) physical activity: which is the energy
expended by a fish moving about,
seeking food, maintaining position,
etc,.
(c) heat of nutrient metabolism:
It is also called heat increment or
specific dynamic action (SDA), which is
the heat released by the many chemical
reactions associated with the
processing of ingested feed.

13. 2. ENERGY SOURCES
The energy needs of fish are supplied by
a) Fats, b) Carbohydrates, and c)
Proteins.
Energy is stored in the chemical
structure of the complex molecules of
feed materials.
When oxidation occurs, energy is
released and trapped by biochemical
reactions and is used to drive the energy
requiring reactions necessary to sustain
life.

14. a) Fats
Fats are the principal form of energy
storage in plants and in animals.
Fat contains more energy per unit
weight than any other biological
product.
The inclusion of fat usually increases the
palatability of a feed.

15. Generally fats are well digested and
utilized by fish.
It is usually estimated that fat provides
8.5 kcal metabolizable energy (ME) per
gramme.
The fatty acid products of digestion are
well utilized by most fish.

16. b) Carbohydrates
Carbohydrates are the cheapest and
most abundant source of energy for
animals.
Most of plant material is carbohydrate.
Carbohydrates in feed material range
from easily digested sugars.

17. c) Protein
In nature, carnivorous fish consume
diets which are about 50 percent
protein.
Fish have a very efficient system for
excretion of waste nitrogen from
protein which is catabolized for energy
and therefore high protein diets are not
harmful.

18. In general, proteins from animal
sources are more digestible than those
from plant sources.
Heating increases the digestibility of
some proteins and reduces that of
others.
Protein is used very efficiently by fish as
a source of energy with good growth,
and cheaper carbohydrate and fat
should be used to supply most of the
energy.

19. Fat 8.5 kcal (ME)
per gramme
Cellulose 3.8 kcal/g
Cooking of
starch
3.2 kcal/g.
Raw starch 1.2 to 2.0 kcal
ME/g.
Protein 4.5 kcal/g
Metabolizable Energy provides
(ME)

20. 3. ENERGY REQUIREMENTS OF FISH
a) Energy Distribution in Relation to
Feeding Level
b) Maintenance Energy
c) Energy Cost of Growth
d) Factors that Alter Energy Needs

21. a) Energy Distribution in Relation to
Feeding Level
 Basal or standard metabolism in fish
is relatively constant under constant
environmental conditions.
 It can change with changes in
temperature and fish size among other
factors.
 The heat of nutrient metabolism is
proportional to the level of feeding.
 The energy excreted in urine and gill
excretions is also a function of feeding
level.

22. b) Maintenance Energy
The energy lost due to standard
metabolism, heat of nutrient
metabolism and physical activity
appears as heat.
The maintenance requirement can be
determined by measuring the heat
produced.

23. The heat production can be
measured directly in a calorimeter
or it can be estimated by measuring
oxygen and applying the appropriate
heat equivalent.
The factor most commonly used is
3.42 kcal/mg O2. Maintenance
energy can also be estimated by
measuring energy loss during
starvation.

25. c) Energy Cost of Growth
It has been shown in mammals that
the cost of growth is fairly constant
after maintenance energy is
subtracted from ME fed.
This probably holds true for fish, but
it has not been experimentally
determined. More research is needed
in this area.

26. d) Factors that Alter Energy Needs
There are several factors which can alter
the energy requirements of fish.
(i) Temperature: As environmental
temperature declines homeotherms
must increase their metabolic rate.
Most freshwater fish do not attempt to
maintain a body temperature which is
different from the environment.

27. As water temperature declines, body
temperature of the fish declines and
metabolic rate is reduced.
The low metabolic rate at low
temperatures enables fish to survive
for long periods under ice where little
food is available.

28. (ii) Water Flow:
Fish which are forced to swim against
a strong current are expending
energy’ still water allows stratification
and the accumulation of waste
products.
Fish rearing facilities should be
designed to obtain maximum use of
water without undue stress on the
fish.

29. (iii) Body Size:
Small animals produce more heat per
unit weight than do large animals.
Small fish should be fed a higher
percentage of body weight than large
fish.
In mammals the metabolic rate is
proportional to the three-fourths power
of body weight (W0.75).
The exponent applicable to fish has
been reported from 0.34 to 1.0. The
factor W0.8 usually used.

30. (iv) Level of Feeding:
The level of feeding also has an effect
on the energy expenditure of fish.
This becomes important in design of
fish rearing facilities.
Dissolved oxygen is usually the first
limiting factor in fish rearing.
The food is oxidized than at higher
feeding levels when much of the energy
is stored as growth.

31. (v) Other Factors: Several other
factors can contribute to high
energy requirements.
Crowding, low oxygen and waste
accumulation are some of these
factors.

32. Fig. Distribution of dietary energy intake in a growing fish
at various levels of feeding. (DE - digestible energy, ME -
metabolizable energy, NEp - net energy for production,
NEm - net energy for maintenance, Hp - heat production)