They look for anemones of course.

In their paper “Reef fishes use sea anemones as visual cues for cleaning interactions with shrimp” published recently in the Journal of Experimental Marine Biology and Ecology, researchers Lindsay Huebner and Nanette Chadwick of the Auburn University’s Department of Biological Sciences explore how these tiny, unassuming shrimp are found on the reef by fish in need of a good cleaning.

Their research focused on the Caribbean Pederson Cleaner Shrimp, Ancylomenes pedersoni, along with the corkscrew sea anemones Bartholomea annulata that they are typically found living with among the reef structure.  What the researchers wondered was how anemone cues were used by fishes to find cleaner shrimp so that they could be cleaned.  Huebner and Chadwick tested this situation by evaluating anemone characteristics with fish visitation rates, and by changing the visibility of anemones and cleaner shrimp in field experiments using mesh covers.

The researchers found that fish visited cleaning stations more often as the size of the anemone increased in addition to the number of crustacean symbionts present. They also found that fishes posed for cleaning at stations only when anemones were visible (i.e. not covered with a mesh cover), regardless of whether shrimp were visible.

These visual cues help fishes find cleaning stations and is also a “previously unknown symbiotic benefit to cleaner shrimp from association with sea anemones.”