Fish need water – well, mostly.
The vast majority of fish spend their entire lifecycle submerged in water, depending on the reliability of rainfall to ensure their habitat doesn’t dry out. Not all fish have this luxury and subsequently, have devised a number of tactics to survive when the rains fail. A remarkable example is that of the family of lungfish which can manage to survive even when their river runs dry. They achieve this in a process known as aestivation. The process starts by an individual forming a burrow in the bottom of the river bed. Whilst within this burrow, they secrete a slimy mucus that keeps their local environment damp. As freshwater is not available that would otherwise provide life-giving oxygen, over millions of years of evolution, they have developed lung-like sacks which enable them to breathe atmospheric air. Their only remaining task is to wait out the dry spell and hope for the rains to return.
Image credit: http://relivearth.com
Tagged in: Aquatic Adaptations