Some animals have evolved to survive without oxygen in extreme environments. Creatures like **Hydra** can switch to anaerobic ...

Animals depend upon plants as an energy source. Chemicals in food are broken down in respiration to create energy stores that can be used by the cell. Animal cells have a basic structure.

If oxygen is absent then respiration can still take place. Animal, plant and yeast cells complete the breakdown of food by carrying out fermentation.

"It may be drawing it from the surrounding fish cells, or it may have a different type of respiration such as oxygen-free breathing, which typically characterizes anaerobic non-animal organisms." ...