- A fish is a kind of aquatic animal
- Gills are used for breathing water by aquatic animals
- Therefore, gills are a part of a fish used for breathing water

- Water contains dissolved oxygen
- Water is a part of an environment
- Therefore, water is a part of an environment that contains dissolved oxygen

- Water is a part of an environment that contains dissolved oxygen
- Breathing is when an animal converts oxygen in their environment into oxygen in blood
- So, breathing is when an animal converts dissolved oxygen in water into oxygen in blood

- Gills are a part of a fish used for breathing water
- Breathing is when an animal converts dissolved oxygen in water into oxygen in blood
- So, breathing is when a gill converts dissolved oxygen in water into oxygen in blood

- Breathing is when a gill converts dissolved oxygen in water into oxygen in blood
- In order to convert oxygen in water into oxygen in blood, fish must take in oxygen from water
- So, fish use gills to take in oxygen that is dissolved in water

So, fish use gills to take in oxygen that is dissolved in water
How do most fish get the oxygen they need to survive?
- Breathing is when an animal converts oxygen in their environment into oxygen in blood 
- Water contains dissolved oxygen 
- A fish is a kind of aquatic animal 
- Gills are used for breathing water by aquatic animals 
- Water is a part of an environment 
- In order to convert oxygen in water into oxygen in blood, fish must take in oxygen from water