Wild fish can tell people apart – at least when they are wearing different-coloured outfits – researchers have found in a study they say could shift our relationship with the creatures.
It is known that certain domestic animals – or those that live close to humans – can tell one person from another, a skill researchers say could be tied to particular humans being more inclined to share resources with them or, conversely, pose a danger. However, such discrimination is less well known in wild animals.
Now researchers have found that wild fish can tell two people apart, apparently by what they wear.
“They are just using simple mechanisms that they use every day in their lives, and they adapt it to [recognise] humans,” said Maëlan Tomasek, first author of the research from Max Planck Institute of Animal Behaviour in Germany.
Writing in the journal Biology Letters, Tomasek and colleagues report how they carried out the study in open water in the Mediterranean Sea.
In the first stage of the study, a researcher spent 12 days training wild saddled seabream and black seabream to follow her by repeatedly offering them food and rewarding those that followed when she swam away.
The trainer was then joined by another researcher dressed in either identical diving gear or diving gear with different-coloured patches and fins. In both scenarios, the two divers swam off in different directions, before returning to the starting point and repeating the process. While both researchers carried food, the fish received a reward only if they followed the trainer.
The researchers carried out 30 trials for each outfit, and used video recordings to count the number of fish following each diver. They reported that, when the divers wore different outfits, both species of fish followed the trainer more often than the other researcher, with this preference becoming more pronounced as the trials went on.
For both species, the team found some individually identifiable fish became better at choosing to follow the trainer, again suggesting the animals were learning which diver to follow.
However, when the divers wore the same outfit, no such effect was seen for black bream, while saddled bream followed the trainer more during the middle batch of trials only. “All in all, when we wore the same outfit, we have no evidence that they could discriminate between us any more,” said Tomasek.
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The team say that, as the fish had no prior experience with humans, it is likely they were harnessing existing capabilities based on visual cues to tell the divers apart. “It shows very simple mechanisms, like pattern recognition or colour recognition can be used, and co-opted to be used, in human recognition,” said Tomasek.
Tomasek added that the study could prompt us to reconsider the way we treat fish, including whether to kill and eat them. “It’s very human to not want to care about them, but the fact that they can care about us, maybe it’s time that we can care about them, too,” he said.
