Freshwater fish are fish that spend some or all of their live in water with a salinity level lower than .05%. Freshwater fish, due to the segmented nature of ponds, lakes, and rivers, are subject to speciation similar to species on islands. Even though only .3% of global water is freshwater, only about 15,000 different species of freshwater fish exist. Freshwater fish make popular pets, while other, larger species, such as salmon, trout, and carp are hunted for food. Freshwater fish have undergone adaptations to survive in freshwater; such as, gills that diffuse dissolved gasses and keep salts inside, scales that reduce water diffusion, and kidneys that reclaim salt from body fluids before excretion.

Freshwater fish, a diverse group adapted to life in rivers, lakes, and streams, exhibit a wide range of anatomical features. They typically have streamlined bodies that reduce water resistance, allowing for efficient movement. Fins aid in navigation, stability, and propulsion. Most lack vocal abilities, communicating instead through vibrations and color changes. Their senses are keen: lateral lines detect movement and vibrations in water, while their eyes are well-adapted to the underwater environment. Gills extract oxygen from water, and some can even breathe air in low-oxygen environments. Scales protect their bodies, and slime coats help in disease prevention and smooth swimming.

The bond between humans and freshwater fish spans millennia, intertwined with our cultural and survival narratives. These fish have long been a vital food source, sustaining communities worldwide. They feature prominently in folklore, symbolizing abundance and fertility. Freshwater fishing is a beloved pastime, celebrated in literature and film.

With the rise of environmental awareness, the conservation of freshwater fish has become crucial, leading to habitat protection and sustainable fishing practices. Organizations and local communities collaborate to maintain biodiversity and ensure the survival of these aquatic species for future generations, recognizing their importance both ecologically and culturally.