iv
Control of Biotic
and Abiotic Factors
in Aquaculture
© 2003 Author
ISBN 81-7035-283-5
All rights reserved. Including the right to translate or to reproduce this
book or parts thereof except for brief quotations in critical reviews.
Compiled and Edited
by
Published by
:
Daya Publishing House
1123/74, Deva Ram Park
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:
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Printed at
:
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Dr Amita Saxena
Associate Professor
College of Fisheries Science
GBPUAT, Pantnagar - 263165
2003
DAYA PUBLISHING HOUSE
Delhi - 1100 035
PRINTED IN INDIA
Contents
Preface
1
1. An Ecosystem
2. Aquatic Weeds and their Control
16
3. Weed and Predatory Fishes and
their Characteristics
51
4. Control of Unwanted Fishes
76
5. Aquatic Insects and their Characteristics
81
6. Management of Aquatic Insects
89
7. Prey-Predator Relationship
94
8. Importance of Soil and Water in Pisciculture
97
9. Importance of Pond Fertility in Fish Culture
108
10. Vertebrate Predators
114
11. Air Breathing Fishes
119
12. Tilapia, Forage Fishes and their Culture
129
13. Composite Fish Culture
134
14. Sewage Fed Fisheries
139
15. Food, Energy and Growth of Fish
149
16. Unwanted Substances (Pollutants),
their Effects and Determination
157
17. Fish, Pathogen, Policies and Spoilage
165
18. Use of Filters in Aquaculture
190
Bibliography
201
Index
207
v
vi
Preface
Fishery is a dynamic multidisciplinary field whose relevance
to farmers is growing more apparent each day. Increased production
is being achieved by the expansion of areas of land and water under
culture and modern farming technology like water, feeds, fertilizers
and chemicals and eradication of predators. This book is an attempt
to bring together available information pertinent to applied value
of fish farming and use of filters to avoid unwanted substances
from fish pond. The definitive compilation of chapters from the
field provides the readers, with information needed for
fundamental understanding.
Without the good will of God, elders and publisher, it would
not been possible to present such kind of work. The overview of
selected topics will satisfy the students and farmers to professional
levels.
This book could easily be expanded if the time had permitted.
If this edition is useful as anticipated next edition will include more
and more improved chapters as per desire of the esteem readers.
Dr. Amita Saxena
vii
v
1
2
Control of Biotic and Abiotic Factors in Aquaculture
Freshwater bodies fall into two broad categories, namely
standing water such as pond and lakes, and running water like
streams and rivers. Standing water referred to as lentic systems
while running waters are called as lotic system. These all come in
limnology.
Chapter 1
Structure of the Aquatic System
Any ecosystem consists of abiotic and bioctic factors.
An Ecosystem
Abiotic Components
Abiotic factors may be of two types–
Introduction
An ecosystem is a unit that includes organisms interacting
among themselves and with the physical environment leading to
clearly defined structure, biotic diversity and material cycle (Odum,
1971).
Aquatic ecosystem, in which the water is the principle external
as well as internal medium may be classified as below Aquatic ecosystem
¯
¯
Fresh water
¯
Lentic
(standing i.e. pond,
lake, ditch, swamp, etc.)
Estuarine
¯
Marine water
¯
Lotic
(running i.e. river,
spring, stream, etc.)
Aquatic habitats fall into three major categories, namely
freshwater, estuarine and marine systems. Though freshwater
habitats occupy relatively small portion of the earth’s surface when
compared with other habitats, they are extremely important to man
as disposal systems. The oceans which cover most of the earth’s
surface not only control the world’s climates, the atmosphere and
the functioning of major mineral cycles but also a major source for
food and minerals. Estuaries are transition zoan between freshwater
and the sea with many unique features.
Freshwater bodies are available everywhere. Even when one
is not easily accessible; it will be possible to make an artificial pond
which will soon be colonised by animals and plants and will show
the same sense of event as in any natural pond.
1.
2.
Physical Factors
Chemical Factors
Physical Factors
The most significant abiotic components, affecting aquatic life
are radiation, temperature, currents, transparency, respiratory gases
and biogenic salts. Temperature, light and conductivity are some
of the physical factors usually measured in any limnological study.
Other physical characteristics such as buoyancy, pressure, viscosity
and surface tension do not tend themselves for easy measurement
but nevertheless play important ecological role. The buoyancy of
water by exerting an upward thrust, helps the aquatic animals and
plants to support their own weight. Water being uncompressible,
there is no significant change in the density of water with increasing
depth. Viscosity of water has an inverse relationship with
temperature. Temperature changes in a water body bring about
changes in the viscosity of water which affect the ability of the small
animals to maintain the position in water. Surface tension is an
important physical factor since small animals like water strides and
snails make use of the surface tension to support themselves on
the surface film.
Radiation
Sun’s radiation sustains two important aspects: one is to heat
the medium resulting in density differences in the water mass,
mixing and chemical alterations plus affecting the suitability of
habitat depending on the temperature tolerance of organisms. The
second aspect is providing light to power photosynthesis by plants,
whether microscopic algae or macrophytes.
An Ecosystem
3
Temperature
Temperature like light, has an important influence on the life
histories of animals and plants. Also, temperature changes produce
characteristic patterns of circulation and stratification which greatly
influence aquatic life.
Distinct temperature layers exist in aquatic habitats because
the surface water expands as it warms up first. This expansion
lowers the density and makes the surface water lighter than the
colder water below. Thus the warm surface water floats on the
cooler water. In between these two layers is a narrow transition
zone called the thermocline. The water above the thermocline is
called the epilimnion, while the cooler, underlying water is referred
to as the hypolimnion.
In any large body of water these two temperature layers may
function as entirely different types of system. It is, therefore, very
essential to carefully delineate these temperature zones in lakes,
large ponds and in oceans.
Turbidity, Visibility and Transparency
These terms are approximately equivalent and refer to the
clarity of water. Both visual and mechanical methods are used to
measure these characteristics of water. Visual methods as could be
expected are subjected to errors and variations, since they involve
the decision taken by the observer.
The light penetrating water alternates with suspended
materials present, restricting the photosynthetic zone wherever
aquatic habitats have appreciable depth. At some depth the energy
harnessed by photosynthesis will only just equal the respiratory
requirements of the plants. This depth is called the compensation
point. Above this depth there is enough light to sustain net growth
and this is called the euphotic zone.
Currents
In streams, currents determine the distribution of vital gases
and nutrients. They also act as limiting factor at species level and
often as energy subsidise that increase productivity at the
community level.
Current and Water Flow
Movement of water is very important in determining the
4
Control of Biotic and Abiotic Factors in Aquaculture
distribution of planktonic organisms, dissolved gases and salts.
They also influence the behaviours of small organisms.
The speed of flow of running water varies from surface to
bottom even in artificial channels where the bottom is smooth
without any obstruction. The current is slowest, close to the bottom.
Such changes in the speed of water are reflected in the modifications
developed by the organisms living in the different levels of running
water.
Depth
A long pole marked out in meters, may be permanently fixed
in the pond and water level read of, when required. Alternatively,
a weighted handline marked or knotted in metres may be lowered
until the weight touches the bottom and the water level read off.
Such measurements should be carried out always at the same place.
This point can be fixed with reference to face permanent land marks.
Specific Conductance
Water becomes as conductor of electrical current when
substances are dissolved in it and the conductivity is proportional
to the amount of dissolved substance.
Chemical Factors
Water being a good solvent varying amounts of dissolved
materials are always present in natural water. The amount of
dissolved materials in the water usually differs from the amounts
present in the body fluid of the organisms living in water. Such
differences affect the osmotic exchange between the animal and
the environment. Apart from this the chemical natural of water
affects the distribution of aquatic organisms. It is, therefore,
necessary to determine the chemical nature of the water before
attempting to study the animals and plants living in it. By and large,
aquatic environments compared to terrestrial environments tend
themselves more early for measurement of chemical factors.
Measurement of Chemical Factors
Measurement of pH, dissolved gases, inorganic salt and
biochemical oxygen demand (BOD) are usually measured in any
ecological study of an aquatic system. Simple method which give
approximate measurement as well as sophisticated production for
extremely accurate estimation.