Ocean pretenders: Eat or be eaten


Algae or  a pipefish pretending to be algae?

At some point or other, all of us have pretended to be something that we are not. From trying to look old enough to buy alcohol as a teenager, to keeping your head low and pretending to be a pot plant in the corner of the office when the boss is looking for someone to take notes during a meeting. Some people might pretend more often than others, people might have good reasons for wanting to look like someone (or something) they are not, and some individuals might have less than innocent intentions when hiding their true identity. The same thing happens in the oceans but the stakes are usually higher than (trying to) look cool with a beer, or the tedium of having to take notes. A critter’s skill at pretending often means the difference between getting dinner or being dinner…

The ocean-pretending I am talking about is more commonly known as camouflage and mimicry. The terms are frequently mixed up or even assumed to be synonyms, but they are two different concepts. To distinguish between the two, it helps to know that the goals of camouflage and mimicry are opposite from each other. Animals using camouflage are trying very hard not to be seen, like you trying to be a pot plant instead of a potential scribe. Mimicry attempts to do the opposite: wanting to be seen, while hoping observers will believe you are someone else, like our teenager bluffing he’s old enough to drink.

Usually when biologists (who know their shit) talk about camouflage, they are thinking of mobile animals that are pretending to be objects or animals that don’t move; these objects could be plants, rocks, sand, sponges, etc. When those same biologists talk about mimicry, they mean active animals that pretend to be different species of active animals. But that is just the start of it, the obvious question is why? What are the reasons behind camouflage and mimicry? As a rule, fish don’t like alcohol, so there must be some other cunning plan.

For camouflage it boils down to two options: defensive or aggressive. People tend to intuitively understand defensive camouflage: hiding so you don’t get eaten or killed. Two ocean examples are seahorses pretending to be seafans or crustaceans looking like sponges. Aggressive camouflage is when an animal tries not to be seen, so it can eat unsuspecting animals coming closer. Frogfish are masters at this, so are most scorpionfish, and many other species. It is perfectly possible for an animal to use both defensive and aggressive camouflage at the same time. Think about the human version: soldiers wearing camouflage do not want to get shot, while aiming their guns at the enemy.

Mimicry has similar uses, depending on what the animal mimics. Unlike camouflage, mimicry needs a distinctive “model species”, which is imitated by the “mimic”. Depending on the nature of the model and the mimic, we distinguish three kinds of mimicry. Batesian mimicry has a dangerous model, but a harmless mimic. Mullerian mimicry has a dangerous model and a dangerous mimic. The last type, Peckhamian mimicry, has a harmless model, but a dangerous mimic.

Batesian mimicry can be compared with our teenager trying to buy alcohol. He might try to look like the real deal, but really is not. A great ocean example is the (non-toxic) baby pinnate batfish (Platax pinnatus), which look like a toxic flatworm. Or baby sea cucumbers pretending to be toxic nudibranchs. Predators assume the mimic is toxic, so they avoid eating it, good news for the mimic!

In Mullerian mimicry both mimic and model are “the real deal”.  This is very common in nudibranchs of the Phyllidiidae family. Most species in this family are very toxic and they all look very much alike. When a predator tries to eat one species, he’ll learn to avoid the other similar looking species as well. A bit like the leather-clad members of different motorbike gangs which look equally dangerous to outsiders. The bikers can tell the difference between other gangs, but I would advise against picking a fight with any of them.

Peckhamian or aggressive mimicry happens when the mimic pretends to be a harmless model, usually to get close to prey. This method is used by predators like dottybacks, who pretend to be harmless damselfish so they can get close enough to juvenile damselfish to eat them. A (purely hypothetical) human example could be a person living in a fancy white house, who pretends to be a silly orange clown, but in reality is a dangerous would-be dictator. As it turns out, land is no different than the ocean: the animals that believe in the illusion are most likely to suffer from it.

Best of Dauin_Lizardfish eating Dragonet

Aggressive camouflage in action: this dragonet failed to see the lizardfish hiding in the sand.

New publication: Fluo frogfish lures

After a weekend looking for vagrant fish in the cold waters of Shark Bay (more about that later this week), I came home to find a pleasant email in my inbox. A new publication has been published online last week. This one is in the journal “Coral Reefs” and is about biofluorescence in the Striated Frogfish (Antennarius striatus), more commonly known as the Hairy Frogfish. The article can be found here, but is restricted access. For those of you who cannot access it, here is what it is about.


Hairy Frogfish by day. Photo: Luke Gordon


As I have written previously, I have been doing a fair bit of work looking at biofluorescence in fishes. During these surveys i had noticed something strange going on with the Hairy Frogfish: their bodies are not fluorescent, but their lure is (very strongly). As you might know, frogfish use their lure as a fishing rod, attracting small fish closer, which are then eaten whole. The fact that the Hairy Frogfish’s lure alone is fluorescent but their bodies are not, hints at the possibility that this fluorescence could be used in what is called “aggressive mimicry”. Aggressive mimicry is the term used for animals who pretend to be something harmless (the “model”) and use that to get close enough to eat their prey.


Hairy Frogfish (Antennarius striatus) with fluorescent orange lure

But the question was, what would it be trying to mimic? Are there animals out there that resemble this fluorescent lure? Cue my last Philippines trip. During a nightdive with the unparalleled science hobbit, we found three more Hairy Frogfish (with fluo orange lures). More importantly, we also found a lot of freeswimming worms near them. Most of them a similar size as the lure of the frogfish, AND the same colour fluorescence as those lures. The resemblance between the lures and the worms went further than just size, shape and movement, but also the fluorescence is imitated. We found our model species!


Fluorescent worm (top orange squiggle) and fluorescent lure (bottom orange squiggle)

This is very exciting, as it is the first time anyone found strong indications that biofluorescence might be used to help fish catch prey. To prove whether it is really used to hunt, lab experiments or extensive observations would need to be done to check if this fluorescence really makes a difference. So while this is a very exciting glimpse into an unexplored part of hunting strategies in the ocean, much more work needs to be done to understand all the details.

If you can’t access the article but want to read it, or you just want to know more, send me an email or ask in comments and I can send the publication to you.

Psychedelic Frogfish!!!

There was some VERY exciting news last weekend, the elusive Psychedelic Frogfish (Histiophryne psychedelica) has been spotted again in Ambon! This very rare and very trippy frogfish has only been described in 2009 and has hardly been seen again since. Practically nothing is known about them, except for the fact that they are amazing! Here is a video (property of Dive into Ambon) to prove it:

The psychedelic frogfish has only ever been seen alive in Ambon and they don’t seem to get much bigger than 10cm. Their exceptional colouration provides excellent camouflage and is thought to mimic coral species like Symphyllia sinuosa, Pectinia lactuca and other corals with similar morphology.

Symphillia and Pectinia

S. sinuosa (A) and P. lactuca (E). Photos: D. J. Hall from Pietsch et al. 2009

As a species of the genus Histiophryne, Psychedelic frogfish are “egg-brooders”, meaning they keep their eggs attached to their body to protect them from predators. It is even believed that they might use their eggs as bait to lure fish in that don’t recognise the eggs are attached to a predator larger than themselves! This is what it looks like:

Psychedelic frogfish_eggs

Psychedelic frogfish with eggs. Photo: Francesca Diaco from Dive Photo Guide

Who could not get very enthusiastic about a fish this bizarre and beautiful? Just too bad I don’t have time to go to Ambon myself any time soon 😉

Holiday special – Feeding time!

Now the main holiday madness is over, we are all starting to take stock of the damage done by the excessive eating and drinking we’ve been doing. Or at least I am doing so… In this time of year, we can all relate to the feeling of being way too full after that unnecessary third helping of dessert. Compared to other animals we’ve got it easy, all we have to do is cook or order our food and start stuffing ourselves. It’s slightly different with the critters we find in the ocean.

Best of Dauin_Lizardfish eating Dragonet

Lizardfish eating a dragonet

While there is a lot of active hunting happening in the ocean, many of the species I study are ambush predators. This means they are even lazier than we are when it comes to getting food. They spend nearly all of their time lying down on the ocean floor, waiting for dinner to swim by and then gulp it down. The plus side of this is they can’t get annoyed with themselves for not ordering the more delicious looking plate their neighbour is wolfing down. The downside is that they sometimes have to wait a long time until dinner swims by.

When you are an ambush predator, being camouflaged is particularly important. If you look like what you really are (a hungry fish), no tasty morsels will be tempted to swim anywhere near your mouth. Camouflage that helps animals hunt is called “aggressive camouflage” and sometimes “aggressive mimicry”. The difference between the two is that camouflage refers to animals pretending to be a plant or dead object like a stone. Mimicry refers to pretending that you (or a part of you) are a harmless or tasty living animal such as a herbivorous fish, worm, …

Synanceia horrida

Aggressive camouflage: Estuarine Stonefish (Synanceia horrida) looking like a rock covered in algae and sponges

Good examples of critters using aggressive camouflage are stonefishes and lizardfishes. They pretend to be rocks or blend in with the sand, waiting for a bite sized morsel to swim by. Aggressive mimicry is used by many species, but it is perfected by frogfishes. They use a modified fin ray as a fishing rod, the bait on top of it (or “esca” if you want to sound all sciencey) has evolved to resemble a small animal like a shrimp or worm. This bait is wiggled around until an unsuspecting fish gets too curious for its own good and ends up as prey. In one species, Antennarius hispidus the esca (=bait) has even been found to contain bioluminescent bacteria, great for luring in snacks at night. Frogfishes are not the only fish using a bait to attract meals, this technique is also used by some flounders and stargazers.

Froggie yawn

The inside of the mouth of a giant frogfish (A. commersoni)

If you have ever had a fish tank and tried to catch your fish bare handed while cleaning it, you will know that no matter how nearby a fish is, it’s hard to catch one. So ambush predators have a number of adaptations to make this easier. Most of them have a huge mouth that sucks in a lot of water when they open it quickly. This suction feeding causes the fish to get sucked into the predators mouth together with the water. On top of that, the teeth of most of these predators are pointed inward, making it easier to hold slippery prey. Another funky adaptation are “pharyngeal teeth”, small teeth on the inside of the throat that hold the prey when the predator opens its mouth to get a better grip on it. You’ve read that correctly, as if frogfish weren’t weird enough already, they also have teeth in their throat.

While most of us only binge eat on special occasions and then feel guilty about it, frogfishes and other similar predators really don’t care. They eat whenever they can, as much as they can. When you think you’re exaggerating, remember this: the mouth of a frogfish can expand to 12 times its normal size when eating. The equivalent of this would be you fitting an entire chicken in your mouth when eating. Frogfishes can also eat prey that are up to 1,5 times bigger than themselves! For us, this would be roughly the equivalent of eating a whole pig for Christmas, which would make for some interesting scenes around the dinner table…


A Scarlet Frogfish with prey in its stomach (source)

So next time you’re feeling stuffed at holiday eating fests dinners, remember it could be worse 😉