Dr Michelle Dickinson: nanotechnologist reveals wild fish can tell humans apart by their clothing

Most people wouldn’t guess ‘fish’ when asked about intelligence in animals, but new research in the journal Biology Letters shows that fish might be smarter than many of us think. 

Previous lab studies have shown that captive archerfish, can recognise human faces in controlled settings, however there is little evidence that wild fish can do the same. 

To learn more about wild fish, researchers from the Max Planck Institute of Animal Behaviour ran experiments to test whether they could distinguish between different humans based solely on visual recognition. 

They started by getting a diver to attract the attention of local fish 8 metres underwater in the Mediterranean sea. The diver wore a bright red vest and fed the fish while swimming in a straight line for 50 metres.  

Every day the diver repeated this process, but started to remove some of the visual cues on their dive gear like the red vest. They also stopped feeding the fish continually during the 50m swim, instead waiting until they had swam the whole 50m with them until feeding them. 

Two species of wild sea bream willingly engaged in the swimming task and after 12 days of training, around 20 fish would reliably follow the diver for 50m in order to get some food at the end. 

In the next part of the experiment, two divers entered the water, with the new diver wearing a different coloured wetsuit and fins.  The divers swam 50m in opposite directions and on the first day the fish were confused as to which diver to follow. At the end of the 50m swim, only the original diver fed the fish and by day two the fish ignored the new diver and followed the original diver who fed them at the end.  

To see how the fish were recognising the original diver as the deliverer of food, the next part of the experiment involved both divers wearing exactly the same colour and style of dive gear. This confused the fish and they didn’t know which diver to follow which suggests that wild fish can quickly learn to use specific cues like colour to recognise individual human divers and is a finding that challenges long-held assumptions about fish cognition. 

This study not only sheds light on the sophisticated cognitive abilities of fish but also prompts a re-evaluation of how we perceive and interact with marine life. 

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Episode Transcript

Speaker 1 (00:06):
You're listening to the Sunday Session podcast with Francesca Rudgin
from News Talks EDB.

Speaker 2 (00:12):
Do you know what I mean? Now for our science
study of the week is doctor Micheldeck and single Morning,
Good Morning. I do love the titles, you know, sort
of your emails you've seen through like wildfish can tell
humans apart by their clothing, and I just think to myself,
of course they can. This is something which scientists have
looked at. This just sounds delightful.

Speaker 3 (00:33):
The study, this is a lovely study. It's in the
General Biology Letters. I love it because the experimental is
just super cute. So you probably don't even think about
whether your fish recognizes you or not, because if you
have a fish in a fish tank, as soon as
you pick up that little food dish, they're all over it.
But are they excited about the food or are they
excited about you? Well, in lab conditions, they have shown

(00:55):
that fish that have grown up in a lab so
captive fish called archerfish, can recognize specific human faces and
who is feeding them. But we've never known if wildfish
can do them. So this beautiful study is and al
to figure it out. So what they did is. They
went into the Mediterranean Sea and they threw a diver

(01:16):
eight meters underwater and tried to get her to attract
attention of the local fish to see what fish would
maybe be attracted to her. And there were some fish
that came along, and she was very distinct. She wore
this bright red vest and then she started swimming fifty
meters in one direction, feeding the fish along the way,
hoping that the fish would learn to recognize that she

(01:36):
is a feeding system and they should follow her. And
she did this every day on repeat. But as the
days went on, she started to remove the big red
vest that she was wearing and some of those big
visual cues. And then at the end, so day twelve,
she only fed the fish after they had followed her
for the whole fifty meters. She didn't feed them along
the way, so they really had to see that she

(01:57):
was coming in follow her for fifty meters as she's
swimming quite fast, and at the end they got a treat. Great,
so they go, okay, so the fish have learned to
recognize this diver with her their red vest, and they went, well,
are they recognizing her or are they just recognizing a
human who's swimming fast. So what they did is they
got another female diver of a similar stature to jump

(02:18):
in at the same time, and she wore a different
colored wetsuit, and then they went go and both of
these divers swam fifty meters in totally opposite directions as
fast as they could. And on day one the fish
were like, well, old on, what's going on? I don't
know who to follow. So they just basically swum around
in a circle and didn't know what to do. But
the original diver, who had been there the whole time,

(02:39):
she fed the fish that followed her at the end
of fifty meters, whereas this new diver didn't do anything.
On day two, the fish were like, okay, don't follow
the other girl, like going back to the original one.
So on day two, all of the fish, and there
were twenty fish specifically that came back all the time
that were part of this study, well that volunteered to
be part of the study, on day two, they all

(03:01):
ignored the new diver and just swam fifty meters after
the original diver who they are been going for. So
how do they know that that was the original diver? Well,
because they had a different colored wetsuit on, which sort
of shows that these fish actually have a cognitive ability
to see visual cues. In this case, it was a
wetsuit color. How do they know that? Because then they

(03:22):
got the divers to wear exactly the same clothes do
the same thing, and the cause the fish were like, Oh,
I don't know who to follow. I don't know what's
going on. So the fish were looking for something specific
around the color of the wet suit or a pattern
on the fin to know who to follow. Now does
this mean that fish can't wildfish can't recognize them in faces? Basically,
the study said, oh, we don't know. We didn't do

(03:43):
the experiment for long enough. So now what we're going
to do is keep doing this and try and put
a mask on where they can actually see the face
of the diver to see whether or not it's just
the color queue of their wet suit, or we can
get them to learn these people's faces.

Speaker 2 (03:57):
But what we know so far is that if you
want to make friends with your you know, if you
have a regular swimming spot and you want to make
friends with the wildlife, we're the same peri of togs
every time.

Speaker 3 (04:07):
And what was lovely about the study and said.

Speaker 2 (04:08):
You'll probably feed them too.

Speaker 3 (04:10):
But it taught us that we're actually how we interact
with marine life. We haven't really thought about it before.
And they are really smart. Fish are really smart. They
are recognizing things. So be nice to the fish in
the ocean. And yeah, if you want to do something
fun on your summer, get a little fish, swim around
for fifty meters and feed them. At the end, I
love it. Where do we find the study of the
shell biology letters. It's a beautiful infancource study.

Speaker 2 (04:31):
Thank you so much for talk next week.

Speaker 1 (04:34):
For more from the Sunday session with Francesca Rudkin, listen
live to News Talks it'd be from nine am Sunday,
or follow the podcast on iHeartRadio