A fish-related question

I hope you realise that when you breathe in, you breathe in about 1% CO2 and the rest is nitrogen and oxygen and argon and other stuff in small amounts. When you breathe out you breathe out 5% CO2. It's not like all the stuff you breathe out is CO2. The rest of that 95% is the same thing as what you breathed in. Fish are no different except they filter water and there's less oxygen in water.

This is correct.