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Water Quality Management (Physical Factors)

 Water Quality Management (Physical Factors)

  • Successful pond culture operations mainly depend on maintenance of a healthy aquatic environment and production of sufficient fish food organisms in ponds.
  • Physical, chemical and biological factors play an important role in governing the production of fish food organisms and fish production in the pond.
  • It helps in the survival and growth of the fish. Hence, fish farmers should take a lot of care to maintain hygienic conditions in the pond, so that they get more profits.
  • If the water quality is maintained with utmost care, the farmers need not spend much money for treatment of the diseases. If the water quality is maintained, the fishes also have a good taste.
  • Water quality is influenced by physical, chemical and biological factors of the water. 

Physical Factors

a. Water Depth

  • Depth determines the temperature, circulation pattern of water and the extent of photosynthetic activity.
  • In shallow ponds, sunlight penetrates up to the pond bottom and facilitates an increase in the productivity.
  • A depth of 1-2 metres is considered optimal for biological productivity of a pond. If the depth is very less, water gets overheated and thus has an adverse effect on the survival of the fish.
  • In arid and semi-arid areas, water depth should be more than 2 metres.
  • The excess water from pond can be removed through pumping or through the use of outlet in the embankment.
  • If the water depth is reduced then from a nearby source it should be filling up.

b. Water Temperature

  • Temperature affects fish migration, reproduction and distribution.
  • Fish pose well defined limits of temperature tolerance with the optimal being 20-32°C.
  • Indian major carps can thrive well in the temperature range of 18-38°C.
  • Wide fluctuations of water temperatures affect the survival of fish.
  • In very low or very high temperatures, the fishes are strained and spend more energy; ultimately growth of the fish is affected.
  • If the water temperature changes to a remarkable level then supplying feed and fertilizer to the pond should immediately be stopped.
  • Replenishment of water from a nearby source, harvesting the table size fish, is some of the corrective measures to be taken for it.

c. Turbidity

  • Water turbidity is mainly due to suspended inorganic substances like clay, silt, phytoplankton, zooplankton and sand grains.
  • Ponds with a clay bottom are likely to have high turbidity.
  • Turbidity reduces sunlight penetration and photosynthesis and hence acts as a Limiting Factor.
  • If the turbidity is due to more suspended particles, they absorb nutrients in their ionic form, making them unavailable for plankton production.
  • High turbidity reduces the dissolved oxygen in the pond water.
  • Turbidity is measured with the Secchi Disc.
  • If the secchi disc disappears at 30-50 cm, the water is productive in nature. If it is not visible at a depth less than 25 cm it indicates the blooming of algae, if it is more than 50 cm, the plankton produced is less in the pond water.
  • In less turbid waters, the aquatic weeds growth is more.
  • In highly turbid waters, the sand grains accumulate in the gills of the fish and prawns, causing suffocation and excessive secretion of mucous and finally leads to fish death.
  • High turbidity can be reduced by adding lime and alum.
  • If the water is more turbid, it should be stored in sedimentation tanks and then used for fish culture tank.
  • If the turbidity is more due to phytoplankton, water from the pond should be changed.
  • Fertilizers have no effect in high turbid waters; hence fertilization of the pond should be stopped.

d. Light

  • Availability of light energy to a fish pond greatly influences its productivity and photosynthesis.
  • In shallow ponds, light penetrates to the bottom and is responsible for lush growth of aquatic weeds.
  • In high turbid waters, the light will not penetrate to the bottom. Due to this, the vegetation at the bottom will decay and produce harmful gasses, which affect the fish and prawn life.

e. Water Colour

  • Water gets its colour due to phytoplankton, zooplankton, sand particles, organic particles and metallic ions in the pond water.
  • Water used for fish culture should be clear, either colourless or light green or blue in colour.
  • Water colour of golden or yellow brown indicates the abundant diatoms.
  • Water becomes greenish in colour when phytoplankton is more, develops a brown colour due to zooplankton and mud colour due to more sand grains.
  • Water with black, blackish green, dark brown, red, yellow colours are not good for culture. These colours are due to the presence of more phytoplankton, bad pond bottom and acids in the water.
  • The red colour of water is due to the presence of high levels of iron and death of phytoplankton (phytoerythrin released).


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