Carps live and breed primarily in freshwater environments. Carp is a freshwater fish native to Asia. The fish filters the water through its gills to get the oxygen molecules inside, hence the many hemoglobins above the gills.

The density of freshwater is not the same as that of seawater, so when a freshwater fish enters seawater, water loss occurs due to the rising salt concentration, resulting in the drying up of gill cells, and ultimately death from lack of oxygen. Therefore, carp are freshwater fish.