Native Fish at Mount Rainier National Park. A native species is defined as one that is naturally occurring in the ecosystem, has the capability of self-sustaining its population, and has evolved alongside unique environments. Native fish species play an integral role in the greater aquatic ecosystem, maintaining ecosystem resilience and playing their part in the food web. Most native fish within Mount Rainier National Park are members of the Salmonidae family – which include salmon, trout, char, and whitefish.