Two common varieties of Hudson River fishes – killifish and herring – lack a lateral line (although they have similar sense organs clustered on their heads). It’s pretty clear that the herring lack a lateral line; however, killifish may appear to have one. The lateral line usually consists of a series of tiny bumps or pores, visible as light shines on the side of the fish from different angles. Careful examination of killifish and herring will not reveal any such feature.

The lateral line is a specialized sensory organ that works as a kind of motion detector, allowing the fish to feel vibrations in the water. This adaptation may help fish school together, find prey, and avoid predators.