1 Role of Water and Soil parameters in Pond productivity Dr. Subhendu Datta Sr. Scientist CIFE, Kolkata Centre, India (A) Need of Water and Soil Analysis for Sustainable Aquaculture Importance of water in aquaculture: If aquaculture is the rearing of aquatic organisms, it is important for an aquaculturist to understand the aquatic medium i.e. water, in which these organisms inhabits. If the water is “bad,” plants and animals won’t grow or reproduce. Animal stressed because of poor water quality are also prime targets for pathogens and parasites. Just as people who work in offices or factories that are stuffy and have smoke or chemical fumes in the air are more apt to be sick, so it is with aquatic organisms grown in poor quality of water. Water is the medium in which fish live, and from which they derive oxygen and nutrients. So the quantity and quality of the water very much affect the prospect of fish culture. As water is the basic element in fish culture, its specific properties as a cultural medium are naturally of great significance in the productivity of a pond. Pure water is unable to support living organisms, but its content of nitrogen, phosphorus, potassium and calcium salts, dissolved organic matter and gases like oxygen, nitrogen and carbon dioxide determine to a large extent the productivity. Importance of soil in aquaculture: The properties of pond soil are of greater significance than is generally realised. When soil conditions are not favourable, the production will be limited. Productivity of fishponds depends on the occurrence of suitable environmental conditions and abundance of fish food organisms. The first step in the food chain (Fig. 1) of a fish pond is constituted by primary food organisms e.g. phytoplanktons, which derive their nutrients from the pond environment and with the help of solar radiation undergo photosynthetic activities. Occurrence of these nutrients in pond water and maintenance of its relevant chemical condition depends largely on the nature and properties of the bottom soil wherein a series of chemical and biochemical reactions continuously take place resulting in release of different nutrients in overlaying water and also their absorption in the soil mass. Considering this importance of bottom soil in maintaining the productivity
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Role of Water and Soil Parameters in Pond Productivity
Regular monitoring of water and soil parameters is required for sustainable aquaculture. Different physical and chemical parameters of water and soil which are responsible for good pond productivity are described in this article.
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Role of Water and Soil parameters in Pond productivity
Dr. Subhendu Datta
Sr. Scientist
CIFE, Kolkata Centre, India
(A) Need of Water and Soil Analysis for Sustainable Aquaculture
Importance of water in aquaculture: If aquaculture is the rearing of aquatic organisms, it
is important for an aquaculturist to understand the aquatic medium i.e. water, in which
these organisms inhabits. If the water is “bad,” plants and animals won’t grow or
reproduce. Animal stressed because of poor water quality are also prime targets for
pathogens and parasites. Just as people who work in offices or factories that are stuffy and
have smoke or chemical fumes in the air are more apt to be sick, so it is with aquatic
organisms grown in poor quality of water.
Water is the medium in which fish live, and from which they derive oxygen and
nutrients. So the quantity and quality of the water very much affect the prospect of fish
culture. As water is the basic element in fish culture, its specific properties as a cultural
medium are naturally of great significance in the productivity of a pond. Pure water is
unable to support living organisms, but its content of nitrogen, phosphorus, potassium and
calcium salts, dissolved organic matter and gases like oxygen, nitrogen and carbon dioxide
determine to a large extent the productivity.
Importance of soil in aquaculture: The properties of pond soil are of greater significance
than is generally realised. When soil conditions are not favourable, the production will be
limited. Productivity of fishponds depends on the occurrence of suitable environmental
conditions and abundance of fish food organisms. The first step in the food chain (Fig. 1)
of a fish pond is constituted by primary food organisms e.g. phytoplanktons, which derive
their nutrients from the pond environment and with the help of solar radiation undergo
photosynthetic activities. Occurrence of these nutrients in pond water and maintenance of
its relevant chemical condition depends largely on the nature and properties of the bottom
soil wherein a series of chemical and biochemical reactions continuously take place
resulting in release of different nutrients in overlaying water and also their absorption in
the soil mass. Considering this importance of bottom soil in maintaining the productivity
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of fish ponds, Hickling (1971) described such soils as the “Chemical Laboratory of the
fish pond.
Fish
Bottom Fauna
------------------------
Zooplankton
Bottom Flora
------------------------------------------
Phytoplankton
Nutrients in water
Nutrients in Soil
Fig. 1: Food pyramid in a pond
The soil fertility is of special importance in the growth of benthic vegetation.
While water fertility will contribute largely to the production of plankton; the pond bed
releases nutrient material into the water and helps in fixation or chemical combination of
such substances released in the pond itself or introduced from outside. Production in ponds
with a bottom rich in fertilising elements is much greater than in those with poor soil. The
colloidal content of the soil, especially of the muddy layer on the top, is of importance in
its capacity to fix or chemically bind nutrients. The productive capacity of the pond
bottom has to be preserved by alternate periods of mud formation and mineralisation – the
practice of regularly draining fish pond.
In view of this importance of overlaying water as well as bottom soil in
determining the productivity of a fish pond, an intimate knowledge about the nature and
properties of these two phases need to be understood thoroughly for developing a clear
idea about the ecosystem and obtaining, thereform, good production of fishes.
Importance of water and soil analysis in sustainable aquaculture: As the fish catch from
all sources of capture fisheries has nearly attained a saturation point, aquaculture has
gained special attention to increase the fish production of the country. To achieve this
goal, with time aquaculture has also shifted from conventional culture practice to semi-
intensive and intensive culture practices. In intensive cultural practices, there is very high
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load of fish, feed, nutrients and chemicals used for controlling fish diseases (e.g.
antibiotics) per unit area. Therefore, fish excreta, respiratory products, unfed materials;
unutilised nutrients/chemicals and transformed/metabolites of nutrients or chemicals can
severely deteriorate the fish pond/lake environment (i.e. water and soil quality) even in
short run. Every system must be sustainable. Fishery resources are renewable source of
resources i.e. fish stock in an aquatic system are able to reproduce or replace themselves or
increase. The management of renewable resources involves, as a minimum, practices that
will result in a sustained yield. This emphasise the management of human use of fishery
resources so that it may yield the greatest sustainable benefit to present generation while
maintaining its potential to meet the needs and aspirations of future generations. In
layman’s language, we should practice the aquaculture in such a way so that present
generation can get the earnings for their livelihood, at the same time, follow the good
management practices and maintain the good fertile condition of the system (i.e. soil and
water) so that it produces fish in the similar way to the future generations. Hence the
importance of water and soil analysis lies for sustaining high yielding aquacultural
practices. Regular monitoring of water and soil quality parameters can give an insight
about the physical, chemical and biological environment of the aquatic ecosystems. This
will assist to take decisions on management practices to be adopted both in terms of better
fish production and maintaining the ecosystem for long run.
References
1. Hickling, C.F. (1971). Fish Culture. Faber and Faber. London. pp.225.
2. Conservation of Natural Resources (2nd
ed) Gey-Harold Smith (ed)- John Wiley &
Sons. Inc. Chapt. 19. Fisheries for the future.
3. Environmental Conservation. R. F. Dasman, John Wiley & Sons. Inc. Chapt. 9.
Water and Fisheries.
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(B). Role of water parameters in pond productivity
Physical Parameters of Water
The major important physical parameters of water on which the productivity of a pond
depends upon are;
1. Depth.
2. Temperature.
3. Turbidity.
4. Light.
Depth : Depth of a pond has an important bearing on the physical and chemical qualities
of water. On it, but varying with its turbidity, depends the limit of penetration of sunlight,
which in turn, determines the temperature and the circulation patterns of the water and the
extent of photosynthetic activity. Ideal depth for different kinds of fish ponds from the
point of view of congenial biological productivity are as follows;
Nursery Pond : 1 – 1.5 m
Rearing Pond : 1.5 – 2.0 m
Stocking Pond : 2.0 – 2.5 m
Ponds shallower than 1m get over heated in tropical summers inhibiting survival of
fish and other organisms. Depths greater than 5 m are also not suitable for fish culture. In
such ponds along with poor penetration of sunlight, there remains the formation risk of a
permanently deoxygenated layer or the circulation of water is unable to carry oxygen
down to the mud layer. Formation of H2S takes place in reduced layer of pond mud and in
absence of oxidizing surface layer, this poisonous gas diffuse into the water and make the
deepest parts of the pond uninhabitable by fish. In such ponds there must be the provisions
of plenty of breeze flowing which can keep water circulating or arrangement of artificial
water circulation (aerator).
Turbidity (Transparency): 1
Transparency ∝ --------------
Turbidity
Transparency is inversely proportional to the turbidity of water, which in turn is directly
proportional to the amount of suspended organic and inorganic matter. *Turbidity due to
profusion of plankton is an indication of pond’s high fertility but that caused by silt or
mud beyond a limit (up to 4% by volume) is harmful to fish and fish food organisms. *
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Turbidity due to high concentration of silt, mud or algal growth causes death of fishes due
to choking of gills. Suspended particles may be settled by application of lime and algal
bloom can be restricted by application of Takazine – 50 (Cymazine) @ 2-4 kg / acre. If
the pond water is covered by floating weeds, Wolfia. sp (microweeds) or Lemna minor,
Lemna major, Spirodella for one week then also the algal growth is checked due to lack of
penetration of sunlight.
Euphotic zone is the visible zone of natural water body. *[Turbidity and
transparency both are optical properties of light, turbidity causes light to be scattered
thereby restricts its penetration and reduce photosynthetic activity. Suspended particles
causing turbidity may also adsorb considerable amount of nutrient elements like
phosphate, K, N2 in their ionic form and making them unavailable for plankton
production, while transparency cause light to be transmitted in straight line through the
sample.]*
Secchi disk transparency : 20-60 cm is ideal for good productivity. It is a metallic plate
of 20 cm diameter with four alternate black and white quadrants (to give a sharper end
point but generally at a smaller depth) on the upper surface and a hook at the center to tie a
graduated rope. The procedure in simply to observe the depth at which the disk let down
from the surface just disappear from view. The observation must be made through a
shaded area of water surface. It is usual to determine the point of disappearance as the disk
is lowered (d1) allow it to drop a little further, and then determine the point of
reappearance as the disk is raised (d2). The mean of the two readings is taken as the secchi
disk transparency.
The observation should not be made early in the morning or late in the afternoon,
though both theory and observations show that the result is largely independent or
illumination. Other instrument to measure transparency are photometer, lux-meter.
Temperature:
Variations in temperature in a water body has a great influence upon its
productivity. Temperature influence all metabolic and physiological activities and life
processes such as feeding, reproduction, movement and distribution of aquatic organisms.
Temperature also affects the speed of chemical changes in soil and water. The oxygen
content of water decreases with rise in temperature. Most of the tropical fish cann’t