Small Fish/Big Pond Sunday

In which we explore happenings in the hydro- and blogospheres.

1) Most ocean enthusiasts know all about the lionfish invasion that currently plagues America’s eastern seaboard and the Caribbean. Lionfish, introduced to the Eastern hemisphere by aquarium traders in the 1980’s, are voracious predators of juvenile fish and are fast becoming the dominant species on many Florida reefs, with predictably catastrophic ecological consequences.

Common lionfish I photographed in its natural habitat: Perhentian Islands, Malaysia. We're accustomed to associating invasiveness with ugliness (rats, pigeons, cane toads) but lionfish are a good reminder that beautiful animals can be insidious little bastards too.

So: how to get rid of ’em? Well, the New York Times has this entertaining video about lionfish tournaments, in which teams of divers compete for $1,000 by killing as many of the invaders as they can. (Or maybe it’s only entertaining to people who professionally killed invasive fish for a summer – I dunno.)

One of the many things I appreciate about the video is that it depicts divers as active managers of ecosystems, warriors on the front lines of reef degradation. The diving community represents a vast potential pool of environmental technicians, and aside from the occasional reef clean-up this potential goes largely untapped. The vast majority of the divers I’ve met would love to be more involved in reef protection.

2) In Japan, the black kokanee, a species of salmon that had been considered extinct for the last 70 years, was rediscovered in a lake near Mount Fuji. When its native lake was converted for hydroelectric use, 100,000 kokanee eggs were relocated to Lake Saiko, yet the transplant appeared to fail. As it turns out, the kokanee are alive and kicking. No doubt the Japanese fishing industry is salivating: a new species to eradicate!

If I were a previously unknown fish species, the absolute last place I'd want to be found is Japan.

3) One of the things I’ve enjoyed most about creating Thirty Below is that it’s given me an excuse to read many other cool marine blogs. There’s a cornucopia of great content out there – which is both inspiring and, for a neophyte blogger trying to carve out a niche, a little daunting. Anyway, among those sites is RTSea Blog, an ocean-news blog run by an undersea film company. This week they got their hands on a press release issued by the team of experts that the Egyptian government called in to analyze the causes of the recent Red Sea shark attacks.

Predictably, the experts concluded that illegal human activity – from fish poaching that reduced the sharks’ food supply to dive operators feeding the sharks themselves – were among the major causes. But the craziest factor?  “The illegal dumping of sheep carcasses by animal transport vessels within 1.2 miles of the shore.”  Uh, yeah, that’ll draw sharks.

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Undersea Penis Fencing! (That got your attention.)

This holiday season, millions of Americans will gush over freshly unwrapped Playstations and electric beard trimmers and other ribbon-festooned bits of electronic junk that will probably end up forgotten in a drawer by March. In all that exulting, one phrase that I doubt will be heard very often is: “Marine flatworms! No way! Oh boy oh boy oh boy oh boy!”

Yet those were the words I gleefully exclaimed last week when Elise’s mother presented me with Marine Flatworms: The World of Polyclads, a lushly pictorialized guidebook to some of my favorite invertebrates. I leafed through the sections on flatworm biology in a state of rapture. My girlfriend’s family looked on dubiously, no doubt wondering what kind of social deviant could possibly get so aroused by amorphous undersea blobs. I tried to persuade them of flatworms’ virtues, pointing fervently to the book’s most spectacular photographs: Check out this beauty, and this one, and this…

Marine flatworm, Thysanozoon sp. How is it that I have a million nudibranch pictures, but no flatties? Copyright Wolfgang Seifarth.

But convincing non-divers of flatworms’ merits isn’t easy. Sure, they’re colorful, but so are M&M’s. They may look pretty in the guidebook, but the page also renders them static, removes them from the context that makes them so spectacular: the reef.  It’s hard to explain how the vibrancy of the reef accentuates the worms’ gorgeous markings, how thrilling it is to find a species you’ve never before seen, how every dive becomes a joyful scavenger hunt for these brilliant invertebrates once you’re in the throes of flatworm mania. (I have equal love for the nudibranch, colloquially ‘sea slug,’ which looks quite similar to the flatworm but is taxonomically very different.)

Phrikoceros sp., copyright Michael D. Miller.

Only once have I seen a flatworm swimming, but I’ll never forget its supple grace, the way the margins of its body fluttered and undulated with heart-wrenching vulnerability: a soft-bodied little thing, detached from the reef that sheltered it, striking out in a vast predatory ocean, with only a thin coat of toxic mucus as protection.

Watch this video (flatworm begins swimming at 0:13) and tell me you’re not enthralled. Video courtesy of Youtube user memutic.

Anyway, I had to convince Elise’s family that flatworms are truly worthy of adulation. I flipped pages desperately, searching for the phrase that would catch their attention, and suddenly there it was – it might as well have been written in neon:


Say the book’s authors, Leslie Newman and Lester Cannon:

When two sexually aroused flatworms approach one another they slowly glide and touch, and then rear up, raising the front half of their body. The muscles around the copulatory structures are tensed and the penis, armed with a fine hypodermic-like hard stylet, is thrust out of the underside of the body and directed towards the partner. Then with deliberate motions each tries to stab its penis into the body of the partner – any part of the body. With short, stabbing motions each worm thrusts its penis stylet through the soft epidermis of its partner and injects a white bundle of sperm. They may do this repeatedly, until each bears multiple stab wounds and white blisters of foreign sperm. Then they lower their penis stylets and glide apart.

I nearly read this paragraph aloud, then realized that a description of a bizarre, rape-like sexual ritual was not the best excerpt to read to the family of one’s significant other. Good thinking, me.

Why do some flatworms engage in this strange behavior? (Only two groups actually penis fence; most flatworms care at least a little about consent.)  Worms are hermaphroditic, capable of being either father or mother, inseminator or inseminatee; so why would they rather impregnate than be pregnant?  The standard explanation is that becoming the mother is more energetically expensive – producing and carrying around a bundle of eggs is a serious drain on a flatworm’s resources. Although the eggs hatch after only a week, that week is still an exhausting and perilous one.

Video created by Leslie Newman – the very same Newman who wrote my guidebook. A strangely intense clip, complete with bombastic orchestral music and inane narration. Courtesy of

Also, fatherhood has an adaptive advantage: victorious father worms, which aren’t saddled with the egg burden, have the potential to inseminate other flatworms in battle and thereby spread their genes even further. Consequently, one would imagine, the entire flatworm population is steadily improving at penis fencing as good swordsmen propagate their genetic material. This strange mating behavior may well be producing a race of invertebrate Inigo Montoyas.

Finally, penis facing is also helpful in telling flatworms from their lookalikes, nudibranchs:

Nudibranchs Flatworms
Taxonomic Class Gastropoda Turbellaria
Breathing apparatus External Gills Respires through skin
Preferred Food Sea Pens Sea Squirts
Mode of Locomotion Crawls with muscular foot Undulates body to swim
Stance on penis fencing No, does not engage in penis fencing Yes, most definitely engages in penis fencing
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Why Do Humans Eat So Many Sea Bass?

“Wild fish did not come into this world just to be our food,” Paul Greenberg writes toward the end of his book Four Fish.  “They came into this world to pursue their own individual destinies.”

Yet the way in which different fish species pursue those destinies – or, if you don’t like that quasi-mystical word, behave as their genes dictate – goes a long way in determining how likely a fish is to wind up pan-seared in butter and lemon juice.

Accordingly, one of Four Fish’s big questions is: Why do we eat certain species?  Well, you might answer, because they’re delicious, or plentiful, or good for you.  But what, specifically, about a fish’s anatomy makes it tasty?  What specific behaviors make it easy to catch?

Take, for example, the European sea bass.  Bass, according to Greenberg, owe their culinary popularity to one organ: their highly evolved swim bladder.  (In Thailand, I discovered, bladder is often served in a dubious dish called “fish maw soup,” which even Thais don’t even seem to like very much.) Greenberg doesn’t go in-depth about what traits make bass’ swim bladders so evolutionarily excellent, so I’ll try to fill in what he leaves out.


A fish’s swim bladder has a basic function: it keeps the fish from sinking.  Without the bladder, the fish would be heavier than its watery milieu, and would have to work very hard to stay afloat.  (Some fish, including sharks and coelacanths, manage this trick.  That’s why sharks have tails with longer upper lobes than bottom – heterocercal tails provide better lift).

A long upper tail lobe provides lift to help compensate for the shark's lack of swim bladder. Picture courtesy of

By filling their bladders with air, fish remain neutrally buoyant – ie, they weigh as much as the water around them – and expend far less energy than they would otherwise.  As fish move up and down, and the water pressure around them changes, they inflate and deflate their swim bladders correspondingly. Anybody who has ever dived has used a Buoyancy Control Device, and understands this intuitively.

Would you eat a soup made of that organ? Ummm... Courtesy of

Now for the cool stuff – how do fish inflate their swim bladders?

There are two kinds of swim bladder: physostomous, or open, bladders; and physoclistous, or closed, bladders.

Human lungs and swim bladders share an ancestral organ, and that homology is very apparent when you look at an open bladder: a duct, like our windpipe, connects the fish’s mouth to its bladder.  The fish simply sticks its head out of the water and gulps some air when it wants to inflate and gain buoyancy; and burps when it wants to deflate.  (Think about Charlie and his grandpa in the original Charlie and the Chocolate Factory.)  Salmon, pike, goldfish, and many other species use this primitive system.

A Yellowstone cutthroat trout with its swim bladder fully inflated. Always nice to be able to use a photo that I took.

But sea bass, like all perciforms (perch-shaped fish), evolved the second, advanced kind of bladder: the closed bladder.  Closed bladders are so-called because they have no duct connecting to the mouth, or to any outside sources of air*.  Instead, perciforms regulate buoyancy by absorbing gas, usually oxygen, from the bloodstream into the bladder; and releasing that gas, when necessary, back into the blood.  To accomplish this, closed-bladder fish have an organ called the gas gland which secretes lactic acid, causing the eventual diffusion of oxygen from the blood into the bladder.  If you’re interested in exactly how this complicated process works, I suggest you consult either this Wikipedia page or a nephrologist.

*Closed-bladder fish have temporarily open bladders during their larval stage (approximately the first two weeks of their lives). A common cause of mortality among farmed fish is closed, or oil-covered, tanks, which prevent the larvae from taking gulps of air. The swim bladder forms around the first bubble of air that a fish swallows; without this bubble, larvae die, sink, or grow up deformed.

The upshot is that fish like sea bass have two big advantages over fish with open bladders: they don’t have to swim to the surface to freshen up their air bladders; and their buoyancy system is simply more efficient – they’re better at staying neutral.  This means they expend less energy than other fish, and, says Greenberg, is why they’re so delicious:

“Without a need to fight gravity all the time, perciforms became more efficient swimmers and were able to trade in their heavy, energy-demanding “red muscle” tissue for lighter, more delicate flesh.  Hence the white, light meat of many perciforms.  Perciforms also evolved an efficient muscle structure that is principally attached only to the central spine column.  The result: a smooth, mostly boneless fillet, very pleasant to eat.”

This unfortunate but delectable sea bass will never again diffuse internal gases across a chemical gradient. Courtesy of

Not only is smooth, delicate, boneless bass flesh tasty to eat, it was once easy to obtain.  Although a closed swim bladder allows its owner to remain below the surface, it also limits the depth to which the fish can dive – go too deep and the bladder may implode.  In general, the fish that can go the deepest, and can change depths most rapidly, are the fish that have no swim bladders at all, like mackerel, sharks, and flounder.  Because coastal sea bass are confined to shallow water by their large bladders, they’re much easier to spear and catch on a line than fish that lack bladders, or have small ones*.

*There are some perciforms, like the Patagonian toothfish (rebranded the Chilean sea bass, in a stroke of marketing genius) which live at great depths. The toothfish’s bladder has been replaced by glands which secrete lighter-than-water fat into the fish’s skin and allow it to maintain buoyancy effortlessly. The toothfish’s high fat content, incidentally, is what makes it so delicious, and thus so over-fished.

The author's brother gets his hands on a sea robin, a bottom-dwelling fish that uses its swim bladder to make drumming noises.

Europeans’ taste for sea bass, then, is the product of fish morphology and centuries of consequent exploitation.  Humans developed and maintained a taste for sea bass centuries ago; began to farm them intensively in the 1980’s; and eat them ravenously today.  All thanks to their remarkable closed-bladder buoyancy system that improves their energy efficiency and, in turn, makes them tastier, less bony, and comparatively easy to catch.  

I’m sure I’ll return to both swim bladders and Paul Greenberg’s great book in future posts, but enough for now. Big hat tip to Davidson Biology for a great site on this subject.

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Titan Triggerfish Will Seriously Mess You Up

The PADI textbook may be rife with information about avoiding the bends, nitrogen narcosis, and rip tides; but it’s relatively silent on dangerous sea creatures.  It offers some perfunctory advice, most of which boils down to “no touching,” yet never mentions which species, exactly, pose threats.  Some animals, like sharks, stingrays, and moray eels, everybody knows to regard with caution.

Others, such as titan triggerfish, don’t seem treacherous until they’re pummeling your face with their teeth.

Triggerfish are simply too goofy to be intimidating. In identification guides, the world’s forty species of triggerfish fall into the ignominious category “Oddly-Shaped Swimmers,” which has to be a little embarrassing if you’re a fish.  Triggers are endowed with huge bulging heads, independently rotating eyes that protrude like marbles, and tiny undulating fins that appear far too small to propel their decidedly un-aerodynamic bodies.  To their credit, triggerfish also have a cool eponymous adaptation: to protect against predators they can raise two dorsal spines, which when locked into place resemble a trigger.  The spines are usually engaged at night.  They still look weird during the day.

An orange-lined triggerfish - a common sighting at Mabul and Sipadan Islands - with dorsal trigger fully engaged. Courtesy of

Despite triggerfish’s benign appearance, our certifying instructor, a normally insouciant Dutchman named Jesse, warned us about them vehemently before we got in the water.  “Ya, ya, they are dangerous,” Jesse told us with uncharacteristic gravity, stabbing at the fish ID book with an index finger.  He was pointing at one species of triggerfish in particular: the titan trigger (Balistoides viridescens if you speak Latin), one of the largest types in the world.

Being an Oddly-Shaped Swimmer probably got this titan triggerfish made fun of on the playground. (Can't believe I just resisted a "school" pun.) Titan triggers are found throughout Indo-Pacific waters; we saw them frequently in Thailand and Malaysia. Image courtesy of

“The triggerfish, she has a nest,” Jesse explained. On a whiteboard he drew a pile of rocks on the seafloor meant to represent the nest.  “She stays near her nest all the time.  And she has a territory around her nest,” he went on, drawing as he spoke, “shaped like this.”

He drew back from the whiteboard to reveal an inverted cone, a funnel, rising from the rockpile.

“You go into her territory…” He shook his head, and pounded a fist – presumably the female triggerfish – into his open palm – presumably a diver’s face.

Titan triggers are capable of delivering a nasty bite. The internet disagrees about whether the bite of the triggerfish is toxic. Eating triggerfish flesh, like the flesh of many reef fish, sometimes causes ciguatera in humans, an illness produced by dinoflagellates in the fish's diets. Whether the bite is ciguatoxic, however, is up for dispute. Image courtesy of

Titan triggerfish, he explained, respond more aggressively to potential predators during mating season: which, being April at the time, it was.  A nasty bite on the arm, a chomp on the rubber fin, and a couple of angry charges had sent several trespassing divers packing in recent days.  (In the future, I was to hear even more tales of triggerfish assaults, including a shattered mask and a cut on the forehead requiring three stitches.)  Titan triggers are not small fish – some are nearly a meter long – and despite being Oddly-Shaped Swimmers they can build up some pretty serious momentum. Not only are they powerful, they’re highly intelligent, and capable of learning from previous experience – if a triggerfish discovers that it can ward off divers by sinking its teeth into arm-flesh, it’s liable to try that tactic again.

For reasons that are not totally understood, titan triggerfish defend a funnel-shaped territory that widens as it rises*.  This means that a diver’s natural reaction to danger – ascension – actually keeps them squarely in the trigger’s defense zone.  An aggrieved triggerfish will keep chasing a frantically rising diver right to the surface, and presumably onto the boat if it could.  The proper response to a triggerfish attack, then, is to swim horizontally and toward the bottom, with fins splayed out to ward the fish off.  Good luck remembering the proper response when you’re being targeted by an enraged yellow missile.

*All species of triggerfish build nests, and most have cone-shaped territories; but only two species- the titan and picasso triggerfish – defend their turf violently. Not coincidentally, these are also the two species big enough to inflict actual damage.


We hit the water that first day with some trigger-related anxiety.  Jesse had warned us that an especially large titan trigger made her home nearby, and that if we saw her we were to cower behind him like the pansies we were.  Screw that, I thought: I’m provoking an attack.  The resultant scar would be a cool synecdoche for a great story.

But when the trigger appeared I obeyed Jesse and ducked.  The triggerfish fluttered awkwardly in a vertical position, facing downward, pecking at the sand even as its body tugged surface-ward like a helium balloon.  Was it arranging its legendary nest?  Hunting for crustaceans and echinoderms, its preferred food?  We were triggerfish neophytes, and there was no telling.

A titan triggerfish feeds on something crunchy and delicious (an echinoderm, crustracean or mollusk). Image courtesy of

We watched the trigger until it drifted off into the poor visibility, and then went on our way.  I’ve encountered many triggerfish since then, and even violated their holy funnels, but no trigger has ever shown the slightest peevishness.  Yet during each interaction I feel the same thrill of unease – there’s something discomforting about the discrepancy between the fish’s inelegant body plan and the menace it poses; it’s like a corpulent cinematic gangster.  I’ll probably end many posts this way, but: they’re wonderful fish.

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Deep Blue Something: An Introduction to Diving at Sipadan Island

A green turtle takes the plunge at Sipadan's Hanging Gardens.

Sipadan Island juts from the floor of the Celebes Sea like a sudden pulse of activity on a seismograph.  An hour by boat from the east coast of Sabah, Malaysia, Sipadan is an innocuous island – lots of sand, lots of palm trees, the occasional lethargic monitor lizard.  It can be circled in fifteen minutes on foot.

There’s little to suggest that below the surface lies one of Jacques Cousteau’s all-time favorite dive sites.

Sipadan Island as seen from above, courtesy of

The island is the remnant of a submarine volcano that erupted on the edge of the Philippine Plate millions of years ago.  After the magma subsided, coral polyps rapidly colonized the newly formed island.  Sea levels soon fell, however, exposing and killing the coral.  The dead coral formed limestone cliffs, as giant masses of calcium carbonate are wont to do, and time passed.

Sipadan Island may once have resembled these limestone karsts in the Andaman Sea, Thailand.

But as the Philippine plate subsided, Sipadan sunk with it, and soon those cliffs were underwater again.  Coral repopulated the shrunken island, radiating outward to create a fringing reef about five kilometers in circumference.  When viewed in complete profile, Sipadan now resembles a giant mushroom, with the reef forming the cap and the limestone cliffs forming the stem.

Sipadan is isolated from Borneo (for the region’s complete geologic history I recommend this excellent blog) by a channel.  The channel is not very wide, but it is 900 meters deep – far deeper than the water that surrounds any other island in the area.  And thanks to this channel, large, weird, pelagic creatures can approach the island.

Borneo is pretty much the coolest.

In the days before we dove Sipadan, divers had sighted a thresher shark, a nocturnal denizen of the open ocean with tennis ball-sized eyes and an immense upper caudal (tail) lobe that it uses to herd and then bludgeon schools of fish.  Thresher sharks are notoriously deep-dwelling and shy – they can only be reliably seen by divers in one tiny pocket of ocean in the Philippines – but the cold, nutrient-rich currents that swirl around the island had lured one from the depths, and it spent a few days hanging out at a dive site called South Point.  That’s the kind of bizarre and spectacular animal you can see at Sipadan – no other island has such deep water so close to land.

We didn't see this beast, but the point is we could have. Courtesy of

As a result of the unusual geology described above, Sipadan features three distinct habitats: shallow coral gardens (the fringing reef); vertiginous rock walls (the erstwhile limestone cliffs); and the channel, a vast and disorienting blue expanse that’s liable to make a diver feel like a speck of phytoplankton.

These three discrete habitats produce an incredible panoply of life, and most dives visit all three zones.  Each dive at Sipadan begins by dropping down the rock wall to a depth between 18 and 24 meters, and hooking up with the prevailing currents that sweep along the wall.  Once you’re in the current’s grip, it’s hardly necessary to swim; you can simply fold your arms and legs, allow yourself to be blown along the rock face like a leaf, and enjoy the parade of sea life.

Drift diving past a terrifying, perhaps carnivorous, rock formation at Sipadan

Floating with the current is known as drift diving, or, more technically, The Conveyor Belt of Awesomeness.  Triggerfish, harlequin sweetlips, lionfish and other reef fishes abound; spiny lobsters wave their antenna cantankerously from their rocky refuges; longnose hawkfish camouflage themselves in the sea fans that bloom from the walls.  The current prevents you from scrutinizing small organisms for more than a few seconds, but scrutinyisn’t really the point – the point is becoming a constituent of the gorgeous tableau instead of a disrupter, harmonizing with the elements instead of fighting them.

Even while indulging in the Conveyor Belt of Awesomeness, you keep one eye on the gaping, featureless blue, for this is where Sipadan’sbig-ticket items lurk.  Each zone contains different species: spotted eagle rays flap phantasmically forty meters down; black-tipped reef sharks skulk past at eye level; green turtles float regally overhead accompanied by entourages of remoras and batfish.  Seeing turtles and sharks is a rarity at most other dive sites; after a few days at Sipadan they elicit yawns.

White-tipped reef sharks, looking nefarious.

A trio of longfin butterflyfish.

After 45 minutes of drift diving, you’re running low on air and nudging your decompression limits.  You rise to five meters and crest the limestone cliff like a climber pulling himself onto a mesa, and before you stretches an effulgent garden of hard and soft corals, softened to pastels by the particulate mist in the water.  Above the coral swarm teeming, intricate fish communities. Large schools favor this ecosystem, including gleaming jacks, squadrons of midnight snapper, and shoals of fusiliers.  Most iconic aquarium fish occupy this sector, too: Moorish idols, butterflyfish, clownfish, yellowtail surgeonfish (one peculiarity of fish identification is that the same species often goes by several different names – you might know the yellowtail surgeonfish as the blue surgeonfish, or the blue tang, or Dory).

Brings a tear to my eye.

The most striking contrast, though, is the light: emerging from the murk of the drift dive into the sun-drenched gardens is not only gorgeous, it produces surges of joy, the sort of internal beneficent upwelling that mothers get from their children, that effeminate British teenagers get from Coldplay.  Not only does the radiant light lift spirits, but the abundance of life, the obvious health of the ecosystem in a region otherwise degraded by overfishing, is encouraging.  No person has ever felt unhappy in a Sipadan coral garden; no person has ever felt anything short of ecstatic.  I can’t prove that, but I’m nonetheless certain of it.

More about Sipadan’s ecology and conservation status pending…

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Today marks the inauguration of my new blog, Thirty Below FishiLeaks: Dispatches from the Undersea Realm.  FishiLeaks tackles the issues that most concern me right now: marine biology/ecology, the conservation of coral reefs and fisheries, and scuba diving. For more about my intentions, check out the blog’s Raison d’etre. I hope that the slim but almost-kind of-devoted fanbase of The Wastivore’s Dilemma will follow this new endeavor with the same lukewarm interest that made Wastivore such a success.

In January, my girlfriend Elise and I are moving to Utila Island, Honduras, to work as divemasters.  (A divemaster is a person who leads other divers around dive sites, pointing out interesting fish, navigating the reef, and preventing customers from touching things that will bite their fingers off.)  I’ve created this blog mainly as a forum for describing that experience, but I’ll also be blogging between now and January about reef creatures, dive theory, and ocean conservation. Through FishiLeaks I hope to keep my own knowledge of marine biology sharp, educate readers on the imperative of protecting marine habitat, and convince my non-diver friends that they need to get certified tomorrow. I generally dislike proselytizers, but these are subjects about which I’m happy to preach.

Thanks for reading!

Ben Goldfarb

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