Total fecundity is about 5,000 eggs. The eggs are cone-shaped and adhesive, clinging to rocks and other structure. Males guard the nests, and turn dark black when spawning. Males are said to die after spawning, but this may not always be the case. Males can live to be 5-6 years old.
Round gobies are benthic throughout their life, even when newly hatched.
Their pharyngeal teeth are ideal for crushing shells. They are selective for small zebra mussels, less than 9 mm in length. Round gobies eat some fish, and are cannibalistic. Many fish eat round gobies, especially smallmouth bass. Male and female round gobies can generally be externally distinguished by their genital papillae.