Physical and chemical characteristics of limnetic environment

Physical and Chemical
Characteristics of Limnetic
Environment

Jitendra Kumar
Department of Fisheries Resource
Management)
jitenderanduat@gmail.com
College of Fisheries, Mangalore

• Physical and chemical characteristics of water
in which aquaculture is to be plasticized is of
prime importance in deciding the suitability of
the water body for successful culture.
• These characteristics would differ depending
on the type of water body.
• i.e.
pond,
tank,
lake,
man-made
impoundment, running water or coastal water
body chosen for culture.

PHYSICAL FEATURES
 TEMPERATURE
 WATER CONDITIONS
 DEPTH
 LIGHT
 TURBIDITY AND
 COLOUR

Temperature
Solar radiation is the source of heat for all water bodies
• Temperature Changes in Small Water Bodies
• Fish Pond Temperature


Thermal stratification in a fish pond

Stratification of water in a natural water body (lake).
Formation of horizontal water current and shearing plane in upper portion (epilimnion) is shown

• Water Conditions And Depth
referred to the temperature change with depth
and thermal stratification. Closely related to
this are the changes in pressure, density,
viscosity, buoyancy etc.
• Pressure
• Density


Light,
The term light was restricted to this visible portion of the radiation
spectrum .
The visible light extends from about 4000 to 7000 angstrom
(1 angstrom (Ao) = 10-8cm).


Spectral radiation of radiant energy

Turbidity
• Turbidity is a condition of water resulting from
the presence of suspended matters
• (1) Settling suspended matters
• (2) Non-settling suspended matters


Secchi disc, a metal painted black and white as shown, attached to a graduated chain for
lowering in the water

Colour
• Yellow - due to clayey turbidity
• - also water overlying a clean sandy area
• Bright-green - water over algae-covered
depression
• Brown - abundance of diatoms
• As fish culturists we have to be familiar with
‘greening’ of water due to algal bloom and
• The reddish-brown colour of blooms of
dinoflagellates

CHEMICAL FEATURES
• The importance of chemical factors, is owing
to their lethal and sublethal effects on
culturable organisms, and also owing to their
effect on biological productivity,
• i.e. productivity of the organism in the food
chain.
• This aspect is discussed separately under
‘Biological Productivity’.


 DISSOLVED OXYGEN
 CARBON DIOXIDE
 pH

 HARDNESS
 ALKALINITY

 CONDUCTIVITY/SALINITY
 NUTRIENT LEVELS

• Dissolved Oxygen
• The concentration of dissolved gases in water
is of prime importance in considering the
quality of water along with the other physicochemical characteristics


an aquaculture pond.
Oxygen levels within the bottom layer of the pond can drop to lethal levels
especially for bottom dwelling culture animals such as freshwater crayfish.

Estimating DO decline during the night

Carbon Dioxide, pH, alkalinity and hardness
• These aspects of water chemistry are closely
linked together.
• All these have great bearing on the quality of
water and these help determine the
productivity of the water body.
• We shall first take up CO2 in water.


Carbon dioxide

• Carbon dioxide content in air is only 0.03%,
but it is highly soluble in water unlike oxygen.
• CO2 stays in free (dissolved) or bound form
(bicarbonate and carbonate) in water
depending on the pH of the water.
• CO2 + H2O⇌H2CO3⇌H+ + HCO-3⇌H+ + CO=3

pH

• pH is defined as a negative
decimal logarithm of the hydrogen ion activity
in a solution.


Diurnal fluctuations of pH will occur due to the amount of aquatic life within a pond.
With higher algae concentrations, more CO2 is removed from the system and
hence pH levels will rise.
The reverse will occur at night when more CO2 is produced therefore
leading to a drop in pH levels.

Ideal change in pH in fish pond with moderate and low alkalinity waters


• pH limit of biological activities in fish

Alkalinity & Hardness

• Alkalinity and hardness are closely related,
since calcium and magnesium
• Which cause most of the hardness of waters
• Generally associated with carbonate minerals
• Which are the principal sources of alkalinity.


An optimum alkalinity level within the pond will prevent extreme diurnal
pH fluctuations.

Acceptable Concentration Ranges for Dissolve Inorganic Substances
in Aquaculture


References
• Odum, E.P.(1983), Basic ecology, Liminiting factors and the
physical environment, pp 221-284.
• Jhingran, V.G. (1991), Fish and Fisheries of India, Fish
culture in fresh water pond, Ecology, pp 273-328.
• http://www.fao.org/docrep/field/003/AC174E/AC174E00.ht
m#TOC
• http://en.wikipedia.org/wiki/Algaculture
• http://www.fao.org/docrep/field/003/AC174E/AC174E00.ht
m
• Waters, Boyd (1998),Acceptable Concentration Ranges for
Dissolve Inorganic Substances in Aquaculture Pond, Water
Quality for Pond Aquaculture
(http :// www.neospark.comimagesWaterqua.pdf)

Physical and chemical characteristics of limnetic environment

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