They do not use a false beard, dark glasses or hide behind newspapers, but when it comes to shadowing others, trumpetfish could give private detectives a run for their money. Researchers say that when hunting, trumpetfish conceal themselves behind other species of fish to approach their quarry incognito. “We see a lot of amazing strategies from animals across the animal kingdom in camouflage and concealment and the ways in which they disguise themselves and they disguise their intent,” said Dr Sam Matchette, the first author of the research from the University of Cambridge. “This will be the first non-human example of a predator using another animal to conceal itself in its approach to its prey.” Writing in the journal Current Biology, the team report how the fish-eating trumpetfish has been observed swimming alongside other, larger fish including stoplight parrotfish – a species that does not feed on other fish. To study whether the behaviour could enable trumpetfish to sneak closer to their prey – a theory Matchette said cropped up everywhere from guidebooks to scientific papers – the team created 3D plastic models of trumpetfish and parrotfish. The researchers deployed the models off the Caribbean island of Curaçao, drawing them on an underwater pulley system past 36 colonies of bicolor damselfish – a species commonly eaten by trumpetfish. When the researchers dragged a trumpetfish model through the water, the damselfish initially swam towards it before dashing away. By contrast, when the model of the trumpetfish was attached to the side of the stoplight parrotfish model, the damselfish inspected the models for a shorter duration and in smaller numbers and – crucially – they fled only when the models were closer to the colony. Similar behaviour was seen in response to the parrotfish model alone. The team say the results suggest that when a trumpetfish lurks close to a parrotfish, it is concealed from the damselfish. “Our experimental results indicate that shadowing behaviour likely reduces detection of trumpetfish by their prey and allows trumpetfish to approach closer to prey before provoking an avoidance response,” the team write, adding the tactic may be particularly useful for trumpetfish if there is a lack of cover from rocky outcrops or vegetation. Matchette added that the models seemed to have been convincing replicas: not only did the damselfish respond to the models as they would towards the real species, but had the models simply been perceived as novel objects, the larger parrotfish model would have been expected to generate a stronger response from the damselfish than the smaller trumpetfish model. Matchette said the study offered new insights into how animals achieve concealment and had wider connotations given the climate crisis was leading to higher ocean temperatures and the collapse of coral reefs. “The degradation of reefs worldwide means that animals are being forced to adapt their behaviour; they therefore may start seeking each other rather than the habitat itself [for concealment],” he said.