Changing Mood

The bluestreak cleaner wrasse – Labroides dimidiatus

The bluestreak cleaner wrasse – Labroides dimidiatus – is a cleaner fish found on coral reefs in the indo-pacific. It eats parasites and dead tissue off other fish’s skin in a mutualistic relationship that provides food and protection for them, as well as considerable health benefits for the other fishes.

Almost all the fish in the reef go to them, in a limited area – the cleaning station – where they pose for the cleaner fish. When posing, the fishes open their gills and pectoral fins, while throwing their heads up. This is their way of asking to be cleaned.

There are several cleaner fish in the world, though this is the most studied due to its Machiavellian intelligence. This fish prefers to eat the mucus and scales of fish, instead of their parasites.  However, the mucus and scales are very important for fish’s protection, so the cleaner fish tries to manipulate the other fish as much as it can, so that it can eat a bit of mucus and scales. Of course, this does not leave the other fish very happy. To try to calm the clients down and try to prolong the interaction, the cleaner fish gives the client a massage with the pectoral fins. These massages lower the cortisol levels, which is a stress hormone.

Did you know?

There have been several studies showing that the cleaner fish has a strong influence on the movement patterns, habitat choice, activity, and local diversity and abundance of a wide variety of reef fish species, which may be of importance considering the strains that the reefs have been put through.


Climate Change

Anthropogenic activities have contributed to an unprecedented increase in atmospheric carbon dioxide (CO2) concentration over the last decades. Indeed, CO2 partial pressure (pCO2) in the atmosphere increased 40% since 1750, and a further rise is expected. Approximately 25% of the emitted CO2 from anthropogenic activities has been dissolve in the ocean.

A decrease of 0.1 units in the pH of surface waters was observed over the last decades, with projections indicating a further decrease between 0.14 and 0.42 units by the end of the 21st century.

Another consequence of rising atmospheric pCO2 is an increase in global surface temperatures, with predictions pointing to an increase of up to 2.7°C by the end of the present century.

Only recently have researchers begun to understand how increasing ocean temperature and pCO2 may affect marine life. Overall, most studies have shown that organisms can be negatively affected by ocean acidification and warming. Environmental changes during the reproductive conditioning of marine species can negatively affect fecundity and offspring survival. Understanding the capacity of organisms to acclimate to the expected changes in ocean pH and temperature is paramount for better prediction of the biological impacts of ocean climate change. This is particularly relevant for tropical species that are less capable for acclimation to climate change.


The scientist

In the 4th grade, José Ricardo Paula had a book about the sea, that had a story about the fish cleaners and their clients. This story caught his attention, and so his interest in Biology grew. 

José decided to enroll in Biology for his University degree. By the end, he saw a poster announcing a thesis theme with a deadline from 2 years prior, regarding cleaner fish. Even though he thought that might be too late, he decided to arrange a meeting, nonetheless. It was in that meeting that it was established that José was going with the team to Australia, as soon as he told his coordinator that, by chance, he was actually taking a professional diving course, at the time. And so, that was the beginning of his master thesis on cleaner fishes. 

Since then, the investigator has kept on studying these fishes, their interactions and their behavior under several stress factors.  



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