Fish Camouflage Better Without Their Friends Around

There’s safety in numbers. 

That’s easy to see (or actually, not so easy to see) with scores of small fish called gobies. New research finds that these fish don’t camouflage completely when they’re in groups, likely because they’re more protected from predators.

Goby is a general term to describe more than 2,000 species of mostly small-sized fish from the family Gobiidae, one of the largest families of fish. They’re found all over the world, particularly in tropical areas. Many are brightly colored with the ability to change their appearance to blend into their surroundings to avoid being detected.

Lead researcher Stella Encel from the University of Sydney first noticed gobies and their camouflaging ability while doing fieldwork in various estuaries in New South Wales.

“Despite careful inspection of the water beforehand, when stepping into the shallows suddenly dozens of previously invisible gobies would reveal themselves as they dashed away,” Encel tells Treehugger.

“Apart from simply being impressed by how so many of these small fish could camouflage so effectively as to completely evade my notice, it also made me wonder how these otherwise defenseless fish (which are prey to a plethora of larger fish as well as birds) were able to sustain such large populations and maintain effective camouflage across such a range of environments (estuaries often contain a range of substrates from pale sand to mixed gravel to almost black mud flats and everything in between).”

Animals get a lot of information about their environment from each other, Encel points out, particularly as it relates to avoiding predators.

“Since camouflage is a predator defense, I was curious what effect (if any) information from other fish might have on their camouflage,” she says. 

Watching Fish Change Color

For the study, researchers collected gobies from mud, sand, and gravel flats in Narrabeen Lagoon in Sydney. In that location, the fish are threatened by larger fish, as well as wading birds, so they rely on camouflage to escape detection.

They took the fish back to the lab where they allowed them to get acclimated to either a white or black background. Then they were tested alone and in pairs against different colored backgrounds to see how they would respond. Researchers used Photoshop to measure what is known as the RGB values (a model for color) of each fish and the background against which they were tested.

They found that when the fish were alone, they were able to match their backgrounds much more quickly than when they were with another fish.

The results were published in the journal Royal Society Open Science.

The Security of a Group

There are a couple of explanations for how being in a group appears to affect how gobies camouflage, Encel says.

First, the “safety in numbers” effect is also known as the concept of risk dilution.

“This is the idea that the more individuals there are in a group, the less risk there is to each individual member of being attacked,” Encel explains. “Since the risk to each individual is reduced, so is the pressure to maintain a high level of camouflage. This allows them to use less energy changing color, leaving more energy for other things.”

Another reason involves the reduced production of stress hormones when in the presence of other fish.

“Being near other individuals is also widely known to reduce fear and physiological stress (a phenomenon known as 'social buffering') in many animals, meaning they produce less stress hormones (i.e. adrenaline, cortisol),” Encel says. “Since these hormones are directly involved in the mechanism of color change, a reduction in stress could also slow/reduce color change.”

Encel and her colleagues aren’t sure if being in a group could ever create a false sense of security and actually put the fish at risk because they haven’t gone far enough to blend into their surroundings.

“The relationship between group size and predation risk is not straight forward. While per capita risk generally decreases with group size, very large groups are more conspicuous than smaller groups, which potentially diminishes this effect,” Encel says. “In this case, the fish were only tested in pairs or alone, we can safely say they are at much less risk when in pairs than they are alone.” 

One of the most interesting things team observed was how quickly the fish can have these dramatic changes in body color. Often they happen with two minutes.

“Also, they do this through sensory mechanisms (their eyes and also light receptors in their skin) without actually being able to perceive their own body color,” she says.

“So they don't know what they look like, but they know what their environment looks like, what other fish look like, and they have an idea of how much danger they're in and they use all this information together to camouflage and ultimately avoid being eaten.”