Director Ambekar E. Eknath, Ph. D Head, APED J.K. Jena, Ph. D ...

Turbidity
Turbidity in culturable water is the resultant effect of several factors like
suspended soil particles, planktonic organisms, humus substances produced
through decomposition of organic matter, etc. Turbidity is measured by
Secchi disc visibility. Optimum Secchi disc visibility in fish ponds IS
considered to be 40-60 cm. Turbidity resulting from plankton is generally
desirable. Guidelines for suspended soil particles value for fish production
are:
Ammonia
Up to 10 000 mgll Freshwater carps, Tilapia sp. and catfishes are
tolerant to this level, however, the effect will depend upon the nature of
the suspended particles.
Pond waters turbid wlth suspended soil particles can be controlled by
application of 500-1,000kglha organic manure. 250-500 kglha
gypsum or 25-50 kglha alum.
The total ammonia concentration in water comprises two forms, namely:
NH3 = unionized ammonia (Free ammonia) and NH4' = Ionized ammonia
They maintain equilibrium as per the equation:
NH, + H20 -+ NH4' + OH'
The un-ionized ammonia fraction IS more toxic to fish and the amount of the
total ammonia in this form depends on the pH and temperature of the water.
As a general rule, the higher the pH and temperature, the higher is the
percentage of the total ammonia present in the toxic un-ionized form Below
are guidelines for un-ionized ammonia level for fish growth:
0.02-0.05 mgll -safe concentration for many tropical fish species;
0.05-0.4 mgll - sub-lethal effects depending on the species; and
0.4-2.5 mgll - lethal to many fish species.
There are a number of measures to maintain safe ammonia concentration in
pond water. Normally at high dissolved oxygen and high carbon dioxide
concentration, the toxicity of ammonia to fish is reduced. Some
recommended measures to reduce the effects of ammonia are:
Aeration will increase the dissolved oxygen concentration and
decrease the increasing pH, thereby reducing toxicity.
Healthy phytoplankton populations remove ammonia from water. Care
should be taken while using fresh manure with high ammonia content.