In Ontario, the Northern Sunfish lives in shallow vegetated areas of quiet, slow flowing rivers and streams, as well as warm lakes and ponds, with sandy banks or rocky bottoms. Northern Sunfish prefer to be near aquatic vegetation where they can avoid strong currents.
During the breeding season, males guard their nests which are made by digging saucer like depressions in gravel or cobble substrates. It eats mostly aquatic insect larvae and algae, but is known for feeding at the water’s surface more frequently than other sunfish.
The Northern Sunfish is a small (about 130 mm long), typical looking member of the sunfish family (Centrarchidae). It has a deep, laterally compressed and olive coloured body with bright blue and red markings. Although the Northern Sunfish looks similar to other sunfish, particularly the Longear Sunfish and Pumpkinseed, experts can tell Northern Sunfish apart by looking at its opercular "ear" flap, which is angled upwards and has distinct red and orange markings.