Which water quality parameter is critical for fish survival?

Dissolved oxygen is essential for fish survival because it is the primary means by which fish and other aquatic organisms obtain the oxygen necessary for respiration. Fish rely on dissolved oxygen in the water to breathe; their gills extract this oxygen as water flows over them. If the levels of dissolved oxygen drop too low, fish can experience stress or even suffocation, leading to poor health or death.

While other parameters like temperature, pH, and nutrient levels also play significant roles in the overall health of aquatic ecosystems, they do not directly impact the immediate survival of fish in the same way that dissolved oxygen does. Temperature affects metabolic rates and species distribution, pH influences various biochemical processes, and nutrient levels can lead to issues like algal blooms, which might reduce oxygen availability. However, none of these factors can replace the critical need for adequate dissolved oxygen in the water for fish to survive effectively.