How do marine animals survive in water without air contact?

Marine animals survive in water by extracting dissolved oxygen directly from their aquatic environment. Unlike terrestrial organisms that breathe atmospheric air, most aquatic animals like fish possess specialized respiratory structures called gills [2]. These gills are richly supplied with blood vessels, allowing for the efficient exchange of oxygen and carbon dioxide between the blood and the gases dissolved in the water [2]. While air contains significantly more oxygen than water, marine life has evolved highly efficient extraction systems to sustain themselves. Some simpler organisms, such as jellyfish, can even absorb oxygen directly through their skin. This dissolved oxygen enters the water through diffusion from the atmosphere, aeration, and as a byproduct of photosynthesis from aquatic plants and algae. Therefore, marine animals do not produce their own oxygen or live without it; they rely on the oxygen molecules mixed into the water.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.6 > p. 89
2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 9: Life Processes in Animals > 9.2.2 Do other animals breathe the same way as humans do? > p. 133