The Pinecone fish, also called the Pineapple fish, has light organs on the sides of its mouth. Bioluminescent bacteria inhabit these organs, producing light and attracting plankton to the fish’s mouth. The fish can turn the light on and off by moving its jaw. This is an example of a symbiotic relationship because both organisms benefit: the bacteria have a place to live, and the fish has a way to eat.
Meanwhile, a parasitic relationship is when one organism benefits while the other is harmed. For example, sea hares can host parasitic copepods in their gills (the copepods only cause minimal damage).