In the zebrafish experiment, which is the independent variable?

• A. Temperature of water
• B. Number of fish at start
• C. Survival rate
• D. Number of tank cleanings

Answer: (A)

The independent variable is the factor you deliberately change to see its effect on the outcome. In the zebrafish setup, you adjust the water temperature and then observe how survival changes at those different temperatures. That makes temperature of the water the independent variable. The outcome you measure, such as survival rate, is the dependent variable because it depends on the temperature you set. Other factors like how many fish start, or how often you clean the tanks, are conditions you would keep constant or control, not the variable you’re purposefully testing.