Fish School

Fight disinformation. Get a daily recap of the facts that matter. Sign up for the free Mother Jones newsletter.


Lemon damselfish. Photo by David C. Cook, courtesy FishBaseLemon damselfish. Photo by David C. Cook, courtesy FishBase
 
In PLoS ONE, a wonderfully intimate study of just how it is baby fish learn to tell friend from foe. Most coral reef fishes spend their larval lives afloat in the deep blue home far from the reef. At the end of their larval stages, they recruit—that is, settle—onto a reef, where the cast of characters is significantly different from those they knew floating around in the open.
 
So how do these little guys learn to avoid the new predators fast? A team of researchers from Australia, the US, and Canada, conducted revealing experiments on lemon damselfish, Pomacentrus moluccensis:

Here we tested the ability of a juvenile marine fish to simultaneously learn the identity of multiple previously unknown predators. Individuals were conditioned with a ‘cocktail’ of novel odours (from two predators and two non-predators) paired with either a conspecific [from its own kind] alarm cue or a [meaningless] saltwater control and then tested for recognition of the four odours individually and two novel odours (one predator and one non-predator) the following day.

 
Photo by John E. Randall, courtesy FishBase.Photo by John E. Randall, courtesy FishBase.


Photo by Richard Field, courtesy FishBase.Photo by Richard Field, courtesy FishBase.Photo by John E. Randall, courtesy FishBase.Photo by John E. Randall, courtesy FishBase.

 The three damselfish predators whose scent was used in the research were, from top to bottom:

  1. Pseudochromis fuscus, brown dottyback
  2. Synodus dermatogenys, clearfin lizardfish
  3. Coris batuensis, batu coris

The experiments revealed that the fish conditioned with the cocktail odors plus an alarm cue made by their own species responded to the scent of a predator by reducing their foraging rate—an indicator of increasing vigilance.* Those fish conditioned to the saltwater controls didn’t.

These results demonstrate that individuals acquire recognition of novel odours and that the responses were not due to innate recognition of predators or due to a generalised response to novel odours.


Lemon damselfish hiding in coral. Photo by Boogies with Fish at Flickr.Lemon damselfish hiding in coral. Photo by Boogies with Fish at Flickr. On the real reef, obviously, some baby fish won’t learn fast enough and will get eaten. Others will learn false associations.

Studies on associative learning have demonstrated that any unknown stimulus can be recognised as a predation risk through associative learning. In natural environments, fishes are constantly exposed to multiple chemical odours. This study highlights the potential for ecologically irrelevant odours to be learned by association when present during a predation event. Responding to irrelevant cues will negatively impact an individual’s fitness.

The lucky ones will live long enough to unlearn the false associations.

It may pay at first to be overly cautious and learn all odours associated with an alarm cue as a predation risk when entering a new environment and then slowly learn which of those actually do not represent a threat.

Sounds like growing up. The paper: 

♥ Mitchell MD, McCormick MI, Ferrari MCO, Chivers DP. Coral Reef Fish Rapidly Learn to Identify Multiple Unknown Predators upon Recruitment to the Reef. PLoS ONE. 2011. DOI:10.1371/journal.pone.0015764

(I ♥ open-access papers.)

*CORRECTION:Thanks to lead author Mat Mitchell who corrected me here in writing that the fish did not jump into their terracotta pots but instead reduced their foraging time in response to the alarm cues and novel odors.

Crossposted from Deep Blue Home.

ONE MORE QUICK THING:

Or at least we hope. It’s fall fundraising time, and we’re trying to raise $250,000 to help fund Mother Jones’ journalism during a shorter than normal three-week push.

If you’re reading this, a fundraising pitch at the bottom of an article, you must find our team’s reporting valuable and we hope you’ll consider supporting it with a donation of any amount right now if you can.

It’s really that simple. But if you’d like to read a bit more, our membership lead, Brian Hiatt, has a post for you highlighting some of our newsroom's impressive, impactful work of late—including two big investigations in just one day and covering voting rights the way it needs to be done—that we hope you'll agree is worth supporting.

payment methods

ONE MORE QUICK THING:

Or at least we hope. It’s fall fundraising time, and we’re trying to raise $250,000 to help fund Mother Jones’ journalism during a shorter than normal three-week push.

If you’re reading this, a fundraising pitch at the bottom of an article, you must find our team’s reporting valuable and we hope you’ll consider supporting it with a donation of any amount right now if you can.

It’s really that simple. But if you’d like to read a bit more, our membership lead, Brian Hiatt, has a post for you highlighting some of our newsroom's impressive, impactful work of late—including two big investigations in just one day and covering voting rights the way it needs to be done—that we hope you’ll agree is worth supporting.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate