There's different colors and sizes of fish in the lake. Some fish are more noticeable then others because they're color blends in more. The variation makes it easier to keep the population from dying out all at the same time.
A flock of birds were flying over the lake looking for food. Most of the blue fish were better hidden then the orange, which made the orange fish stick out to the birds more. While the orange fish stuck out more, the blue fish looked like they were a part of water. The blue skin color helps them blend in more.
The birds started to fly down to see if they can catch any of the fish. When they went down they didn't really see the blue fish at all, making them focusing on the orange ones. The blue skin color helped them hide from the birds
The birds ate almost all of the orange fish, but they didn't eat any of the blue fish. The orange skin color made the fish stick out in the blue water, which was a disadvantage for them. The blue skin color made them blend in with the water, which was an advantage, keeping them alive. This is natural selection because the blue skinned fish have an advantage to adapt.
Since there were more blue fish then orange, they reproduced faster. As time went on, the blue fish population increased much faster then the orange. The blue skin shows natural selection because they can hide from predators and protect themselves, unlike the orange fish, making them the better adapted fish.
The blue fish have a bigger population then the orange as time goes on because the orange fish can't hide as well. There are still a few orange fish, but a lot of blue, making there be little variation between the fish population. The blue skin color for a fish is better because they can hide in the water without being noticed from above or the sides, to where the orange fish pop out to predators. This makes blue fish have a better chance in surviving, making them able to adapt. This shows natural selection because the blue fish are better adapted and are able to survive better.