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72. Reef Stonefish (Synanceia verrucosa) (Utile dulci strategy ?)


The stonefish has elevated camouflage to a form of art: matching colouration, adjusted skin texture, algae coverage and the ability to lie immobile for hours make it almost indistinguishable from the rocks on its side. It takes a while before you realise that the stone or sponge you are looking at is actually a fish.

Is the Reef Stonefish (Synanceia verrucosa) in this underwater videoclip lying in ambush in a cleaning station that is run by White-banded Cleaner Shrimp (Lysmata amboinensis)? Is it just enjoying a good cleaning, or is it combining the useful with the pleasant (a cleaning before or after dinner, thus combining the necessary with the pleasant or as they say in Latin "utile dulci")?

However, stonefish do not really need a cleaning of their skin, at least not a cleaning of dead tissue. They are capable of sloughing their epidermal layers, and having a skin with an accumulation of algae and other fouling organisms helps the stonefish with its near perfect camouflage.

The stonefish in this underwater videoclip has a lot of orange coloured patches; this is the stonefish's natural skin colour. It is only when the layers of discarded keratinised epidermis accumulate that the stonefish becomes darker like the rocks on a reef and really starts to blend in with its environment.

Stonefish are not only eaters of all kinds of fish breeds but also big consumers of all kinds of shrimp species. Predation on cleaning shrimp, a species that is not really beneficial to the stonefish's well-being, cannot be excluded. Maybe a cleaning station provides this ambush predator with a constant and easy supply of good-tasting shrimp?

Usually, when cleaner shrimps venture near or around the mouth of a fish at a cleaning station, the fish will open its mouth slowly and gently or sometimes even being encouraged by the shrimp to do so. By opening its mouth, the fish invites the shrimp or sometimes the cleaner wrasse to enter. Often, the richest pickings are small leftovers that are stuck between the fish's teeth. In the 50 minutes or so I was filming and observing this particular stonefish, I didn't witness the stonefish opening its mouth a single time.

Therefore, I’m not inclined to believe that these shrimp actively took part in cleaning this stonefish. I was actually waiting for the stonefish to open and stretch its mouth and to watch the White-banded Cleaner Shrimp enter. This would have provided me with stunning behavioural footage. Unfortunately, it didn't happen.

When you take a good look at the footage, you will remark in the right corner behind the stonefish a small gathering of rather nervous behaving cardinalfish. This is telling me that the cardinalfish are probably aware of the stonefish's presence.


Patience is key. It took me almost an entire hour to have a mere 30 seconds of broadcast-able quality underwater video footage of this extraordinary behaviour. But just as with everything in life, good things will come to those who are patient. I ran, unfortunately, low on air and had to leave the water, so I have no idea if the "utile dulci" theory is real stonefish behaviour. Personally I have witnessed other stonefish on other cleaning stations behaving in a similar way. If the stonefish effectively lies in ambush, then this is a brilliant hunting strategy.

Filming location:

This short underwater videoclip has been filmed in Mauritius 🇲🇺

More on this topic:

For another in-depth description about the Reef Stonefish please go to our vlog post 175 or click on this link: https://www.beyondscuba.com/post/a-reef-stonefish-synanceia-verrucosa-reveals-it-selves-by-moving

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