Animals display a wide variety of anti-predatory responses. From living in social groups to camouflaging themselves, species have adapted ways to protect themselves and others from potential danger. For many fishes, there’s another way to avoid predation – and it’s hidden in their skin.
Alarm cues can help fish learn about predators
Within their skin cells are chemical components broadly referred to as ‘alarm cues’. These cues are designed to communicate risk to fellow fish. When a fish is injured, say when attacked by a predator, these alarm cues are released into the water, alerting neighboring fishes via smell about the potential danger.
Alarm cues also provide fish with the opportunity to become teachers. When paired with other smells, alarm cues can be used to train fish to associate new smells with danger. So, when these fish encounter that smell again, they will treat it as a threat. This information can then be passed on to naive fish who have not made the same association, much like how a new pupil learns from a more experienced teacher!
The passing of information between individuals – called ‘cultural transmission’ – can occur between social aggregations of fish such as schools or shoals. This is important to ensure coordinated anti-predator responses. It can even be passed from parents to offspring, with offspring using their parents as a means to learn about their environment and its risks.
A dangerous climate
While many fish species appear to handle predation risks without too much trouble, the threat of climate change may result in dramatic change to the senses of several marine species.
Oceans are responsible for absorbing some atmospheric carbon dioxide, which results in the water becoming more acidic. This rise in acidity can impact biological processes, including the olfactory system (i.e., smell). When exposed to higher than expected carbon dioxide level (levels anticipated in the near future), several marine fish species have shown impaired anti-predator responses due to their inability to detect alarm cues.
Changes in climate may essentially act like a nose plug for fish, limiting their ability to detect risk accurately and potentially leading to increased mortality from predation. In time, this may lead to drastic ecological alterations, with fish species facing greater challenges in how they can assess danger. After all, they may not smell it coming.
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Porteus CS, Hubbard PC, Webster TMU, van Aerle R, Canario AVM, Santos EM, Wilson RW. (2018). Near-future CO2 levels impair the olfactory system of a marine fish. Nature Climate Change. 8: 737-743.