Explanation

In commensalism, association between members of different species is made in the way that one is benefitted and neither is harmed, e. g., small fish (sucker fish) gets stuck near the bottom of a shark with the help of its holdfast (modified dorsal fin) vand is dispersed to distant areas. It also gets protection (due to association with shark) and derives its nutrition also. However, the shark does not get any benefit or harm from the sucker fish.