How does mutualism work between a shark and the remora fish?

The symbiotic relationship between pilot fish and a shark may be what is is called commensalism. In this type of symbiOSes, the pilot fish benefit, and there is no known effect on the shark.

But this is not certain. The pilot fish does eat bacteria and dead skin off the shark, and this may actually be enough benefit to justify the relationship. The pilot fish do not, however, lead a shark (or ray, or turtle) to food.

The pilot fish consume small scraps, parasites, crabs, etc. that are associated with shark prey.