Imagine trying to survive in the oceans and the rivers that flow into them. For many animals, a habitat like this would be impossible. Yet the salmon, a fish about 70 centimeters long for many kinds, thrives there, thanks to features that scientists call adaptations: traits that help a living thing survive in its environment.
Consider a strong, muscular body: this adaptation lets it swim upstream and leap up waterfalls. The word upstream refers to against the flow of a river. Equally important is a body that can change from living in salt water to fresh water, which lets it move between the ocean and rivers. Without these traits, the salmon would struggle to last a single season.
As a carnivore, the salmon is an animal that eats other animals; it depends on insects, shrimp and small fish. Its behavior matters as much as its body: it swims back to the stream where it hatched to lay its eggs. Behaviors like this are adaptations too, even though you cannot see them in a photograph.
The next generation faces the same challenges. Young salmon, called fry, depend on their surroundings and on adult care. Young salmon stay in rivers for months or years before swimming out to sea.
Perhaps most remarkable of all: salmon may use their sense of smell to find the exact stream where they were born. Facts like this remind us that every animal's body tells a story about the place it lives.