Fish protein is one of the primary sources that provide food security to the rapidly rising population of the planet Earth. It has been documented that several fish species exhibit a change in their sensory behavior during their stay in water bodies with low pH. The spawning pattern of fish is also affected if the pH level changes. A significant variation in finfish juvenile diversity and population size is observed in few experimental sites in the mangrove dominated Indian Sundarbans over a period of more than three decades (1984–2018), which is directly related to gradual lowering of pH as depicted through a time series analysis of aquatic pH in and around the deltaic complex. The chapter also presents an interesting change in the spawning zone of Indian shad (Tenualosa ilisha) which has shifted towards the downstream direction of the Hooghly estuary with the passage of time.