What is in water that makes fish live?

It's not just one thing, but a combination of factors that make water suitable for fish to live:

* Dissolved Oxygen: Fish breathe oxygen just like we do, but they extract it from the water. Oxygen dissolves in water, and the amount depends on factors like temperature and pressure. This is why fish need moving water to get enough oxygen, as flowing water absorbs more oxygen.

* Water Temperature: Fish are cold-blooded and their body temperature is dependent on the water temperature. Each species has a preferred temperature range, and extreme temperatures can be fatal.

* Salinity: The amount of dissolved salts in water impacts fish survival. Some fish live in saltwater (like ocean fish), some in freshwater (like river fish), and some can tolerate a wide range of salinity.

* Nutrients: Fish need nutrients from their food, but also from the water itself. This includes minerals like calcium, magnesium, and phosphorus, which are essential for bone development and other bodily functions.

* pH Level: The pH level of water indicates its acidity or alkalinity. Fish are sensitive to extreme pH levels, and each species has a preferred range.

* Water Pressure: Fish living at different depths experience different water pressures. Their bodies are adapted to these pressures, and sudden changes can be harmful.

In addition to these, the water needs to be clear enough for fish to see, and it should be free of pollutants that could harm them.

So, it's not just a single ingredient in water, but a balanced combination of factors that make it a suitable habitat for fish.