Water Quality Parameters
Let me discuss about water quality parameters for fresh water aquaculture species i.e Rohu, Katla, Mrigal (Indian major carps). You may ask me why we are discussing about IMC. By volume, Carps account for the largest component of fish culture production globally. Let us discuss about the role of temperature in Carp production. Carps are temperate and warm water species. So water temperature is an important parameter in fresh water aquaculture. 28°-32° C is favourable temperature for optimum fish growth and life cycle activities. Any deviation from the favourable limits, fish feeding and growth comes down. Any drastic deviation results in fish becoming weak and are prone to diseases. Minimum temperature for reproduction is 20° C.
Water temperature vary in summer, rainy and winter season in the same pond. Similarly there is a change in temperature from morning to noon and then up to night. Water temperature is more in upper layers and gradually lesser in the lower levels. If the pond is 2 meters deep, there will be a safe place for fish in such ponds.
In shallow ponds (0.75 to 1.0 meter depth), water gets heated up during day time and gets cooled up during nights. Hence safety zone gets reduced in shallow ponds. If there is a drastic difference between day and night temperature frequently, lot of energy is being wasted and growth comes down. Fish becomes weak and are prone to diseases. Moreover, dissolved oxygen(DO) levels comes down with increase in water temperature. Ammonia damage increases with increase in water temperature, phytoplankton availability increases and produces more oxygen and P.H level also goes up.
Fish stops feeding when water temperature is between 2°-20°C and 34°-38°C. Fish being poikilothermic animals (meaning cold blooded), means that their body temperature is regulated by the surrounding temperature of the water, and their body functions respond and change according to the water temperature. The activity and metabolism of fish is greatly reduced which is why they do not feed during the cold periods and are prone to diseases which is a big problem in winters. In ponds with 1.5 to 2 meter depth, temperature drops down but it is more in lower strata. This is known as stratification in the pond. After prolonged summer, if there is a sudden rainfall with dense clouds, water gets mixed in both top and bottom in the pond. This sudden change leads to mass mortality of the fish. One should be careful about this sudden cooling days and stop feeding the fish to reduce the mortality.
-V Ramachandra Raju
SIFA (Society for Indian Fisheries & Aquaculture)