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 Dr Amita Saxena Associate Professor College of Fisheries Science GBPUAT, Pantnagar - 263165 Published by : Daya Publishing House 1123/74, Deva Ram Park Tri Nagar, Delhi - 110 035 Phone : 27103999 Fax : (011) 27199029 e-mail : dayabooks@vsnl.com website : www.dayabooks.com Showroom : 4762-63/23, Ansari Road, Darya Ganj New Delhi - 110 002 Phone: 23245578, 23244987 Laser Typesetting : Classic Computer Services Delhi - 110 035 Printed at : Chawla Offset Printers Delhi - 110 052 2003 DAYA PUBLISHING HOUSE Delhi - 1100 035 PRINTED IN INDIA
Contents Preface 1. An Ecosystem 2. Aquatic Weeds and their Control 3. Weed and Predatory Fishes and their Characteristics 4. Control of Unwanted Fishes 5. Aquatic Insects and their Characteristics 6. Management of Aquatic Insects 7. Prey-Predator Relationship 8. Importance of Soil and Water in Pisciculture 9. Importance of Pond Fertility in Fish Culture 10. Vertebrate Predators 11. Air Breathing Fishes 12. Tilapia, Forage Fishes and their Culture 13. Composite Fish Culture 14. Sewage Fed Fisheries 15. Food, Energy and Growth of Fish 16. Unwanted Substances (Pollutants), their Effects and Determination 17. Fish, Pathogen, Policies and Spoilage 18. Use of Filters in Aquaculture Bibliography Index 1 16 51 76 81 89 94 97 108 114 119 129 134 139 149 157 165 190 201 207 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
Introduction Chapter 1 An Ecosystem 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 - Ø Lentic (standing i.e. pond, lake, ditch, swamp, etc.) Aquatic ecosystem Ø Ø Ø Fresh water Estuarine Marine water Ø 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 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. Structure of the Aquatic System Any ecosystem consists of abiotic and bioctic factors. Abiotic Components Abiotic factors may be of two types 1. Physical Factors 2. 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 4 Control of Biotic and Abiotic Factors in Aquaculture 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 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.