The researchers tested how harmful nickel is to Nile tilapia fish by exposing them to Nickel Chloride. They wanted to see how this metal affects the fish's health. The study found that Nickel can be toxic to the fish, causing changes in their bodies and blood. The researchers used a test to see how deadly Nickel is to the fish, and found that it can be harmful even at low levels. This shows that Nickel pollution in water can be dangerous for aquatic life like Nile tilapia.