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Water Quality Management (Biological Factors)

Water Quality Management (Biological Factors)

Phytoplankton Bloom

  • The sudden increase of population of certain planktonic algal group as thick mass in water is called Phytoplankton Bloom.
  • It is identified by the deep green or blue green or reddish green colour depending upon the plankton present in the pond water.
  • During the day time phytoplankton produces excess oxygen and during night and cloudy days they absorb dissolved oxygen from water for their respiration resulting depletion of dissolved oxygen and fish mortality.
  • The death and decay of algae also cause depletion of dissolved oxygen.
  • The reason for this algal bloom in pond water is the presence of excess nutrients in water.
  • Chemicals like Copper sulphate @ 0.1- 0.5 mg / lit of water or diuron@ 0.3- 0.5 mg / l of water also helps in controlling this bloom.

Disease Causing Agents

  • The most important aspect of water quality management in the culture system is to maintain fish without disease causing agents and under hygienic conditions.
  • The diseases in fishes are caused by bacteria, virus, fungi, protozoa and crustacean parasites.
  • These parasites enter into the pond along with water, fish or prawn seed and nets from other infected ponds. Due to the unhygienic conditions, these parasites cause diseases in fish and become less resistant to diseases.
  • Due to parasitic infection, the growth rate reduces and finally fish dies.
  • To avoid these bad effects, use good and healthy material and fish should be examined once in 15 days.
  • Abnormal behaviour of fish and prawns is observed in infected ponds. These should be observed and immediate action should be taken. Otherwise, whole crop could be vanished.
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