Physical and chemical characteristics of limnetic environment
Physical and Chemical
Characteristics of Limnetic
Department of Fisheries Resource
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.
impoundment, running water or coastal water
body chosen for culture.
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.
The term light was restricted to this visible portion of the radiation
The visible light extends from about 4000 to 7000 angstrom
(1 angstrom (Ao) = 10-8cm).
Spectral radiation of radiant energy
• 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
• Yellow - due to clayey turbidity
• - also water overlying a clean sandy area
• Bright-green - water over algae-covered
• 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
• 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
• This aspect is discussed separately under
• 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
• 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 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 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
• 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.
• Waters, Boyd (1998),Acceptable Concentration Ranges for
Dissolve Inorganic Substances in Aquaculture Pond, Water
Quality for Pond Aquaculture
(http :// www.neospark.comimagesWaterqua.pdf)