Warming water and pollution amplify fish mortality in Kerala during summer

Subject :Environment

Section: Pollution

Context: Warming water and pollution from industries, chemicals and pesticide run offs, lead to fish kill during summer months.

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A study published in August 2022, predicts a six-fold increase in the frequency of fish mass die-offs across the world by 2100 due to summer kills (mortalities associated with warm temperature), winterkills (mortalities associated with cold temperatures) and infectious pathogens.
In the lakes of the northern hemisphere, it has been observed that warming of water amplifies the frequency of fish mass mortality events.
In Kerala, the month of May with high temperatures has typically recorded the most fish kills – the phenomenon when a large number of fish in a particular area die and float on the surface within a short period of time.

Causes of Fish Mortality:

Low water flow and oxygen
- Rapid changes in temperature affect a wide range of fishes regardless of their thermal tolerance. Each organism has its own levels of tolerance for low dissolved oxygen, but levels under 3mg/L are largely toxic to fishes. They are often seen coming to the surface of water and gasping for air.
- Fishes are very sensitive to changes in water quality, the pH of the water, salinity and oxygen quantity. These changes can disrupt the ecological balance in the water bodies, leading to the growth of harmful algal blooms and other aquatic pathogens.
Water pollution
- Excessive amount of chemicals used in agriculture and their run-off are also a major concern. These chemicals accumulate in the water and is toxic to fish causing respiratory and reproductive disorders.
- The excessive use of chemicals in aquaculture, such as antibiotics and pesticides may also lead to fish kills.

Prevention of fish kills:

Adopt sustainable practices in aquaculture, reduce pollution and promote conservation of water bodies.
Increasing green cover is very important strategy to prevent fish kills.
The dams should release enough water into the rivers in summer to allow at least a minimum flow.
An oxygen diffuser should be used in fish farms and ponds