Where does the oxygen come from that aquatic organisms need?

The oxygen that aquatic organisms need can come from a variety of sources, including:

- Dissolved oxygen: This is the oxygen that is dissolved in the water. It enters the water from the atmosphere through diffusion, and can also be produced by photosynthesis from aquatic plants.

- Photosynthesis: This is the process by which aquatic plants use sunlight to convert carbon dioxide and water into glucose and oxygen. The oxygen produced by photosynthesis is released into the water.

- Respiration: This is the process by which aquatic organisms use oxygen to break down food for energy. The oxygen used for respiration is taken in from the water through the gills or body surface.

- Diffusion: This is the process by which gases move from an area of high concentration to an area of low concentration. Oxygen can enter the water from the atmosphere through diffusion.

In addition to these sources, oxygen can also be added to water through artificial means, such as by using an air pump or by bubbling air through the water.