IT’S INTERESTING HOW MANY THINGS you meet under water that could kill you. Few people would crawl around voluntarily with cobras, centipedes or scorpions, but under water we seem to delight in cosying up to potentially lethal critters.
I had a lovely time photographing a group of striped reef catfish in Lembeh the other month, backing away chuckling as they swarmed over and tickled my knuckles, trying to pull away far enough to focus on them.
Later I remembered something about them having venomous spines, so I looked it up on Google.
Apparently those lethally toxic spines were millimetres away from my fingers.
Most people who swim in the sea are familiar with the business end of jellyfish, some with their even more dangerous cousins the siphonophores and box jellies. Sea-snakes and blue-ringed octopuses can, with the tiniest of bites, paralyse and cause death by asphyxiation. Cone shells and certain sea urchins can be lethal. Steve Irwin was famously killed by a sting ray – and there are many more.
These potent venoms, spines, stings and teeth have very specific uses, however. You have to be trying quite hard or doing something extremely foolish, or just have really bad luck to earn a dose of these poisons.
Most of the toothed, spiny and incredibly venomous marine animals we regularly encounter are not even vaguely interested in using their lethal armaments, other than as a last-resort defence.
One group of venomous animals is more familiar to, and indeed actively sought out by, large numbers of divers, particularly photographers.
Scorpionfish and their relatives make superb photo subjects. Not only do they habitually lie still, but the textures and colours they use as camouflage, the flaps and algae growing on their skin, their large, upturned mouths, their fanlike fins and spiky cheeks, even their reflective eyes, add up to some of nature’s most spectacularly decorated – and photogenic – art forms.
Scorpionfish are heavy-headed and heavy-chested bottom-dwelling fish, with characteristic broad fanlike pectoral fins and a tapering tail.
They are characterised by a broad bony plate on the cheeks, usually with thornlike spines on it, giving the group the name “mail-cheeked fishes”.
Their heads tend to be plate-armoured and often spiny, their bodies covered in heavy scales.
They predate on a variety of near-bottom fish and invertebrates, usually caught by lying in wait and slurping the prey into their cavernous mouths.

WHAT WE THINK OF AS “classic” reef scorpionfish and lionfish are mostly members of only one of around 30 closely related families and more than 1200 species that make up the order Scorpaeniformes.
Most fish, scorpionfish or not, have spines on their fins, and almost all have skin glands that produce protective skin mucus, some of these glands associated with the fin spines.
This mucus is often an irritant, if not an outright dangerous toxin. Push onto the spine of any fish and you’ll probably crack the skin sheath to the spine and inject a certain amount of mucus, often earning yourself a local infection.
I’ve never been able to find a comprehensive list of exactly which fish have “overdeveloped” the spine glands specifically to produce injectable venoms, but the reef scorpionfish group is the classic example.
A handful of families, most of them tropical – notably the scorpionfish, waspfish and stonefish families, but also the flatheads and some sculpins – have developed their venom glands on the dorsal, anal and pelvic fins to act as syringe-like deliverers of potent venom.
On gurnards and most of the coolwater members of the scorpionfish group, the mucous and spine glands are a somewhat milder irritant.
I always seem to meet someone who knows someone who got stung rather than anyone who has themself been stung, but the story is overwhelmingly the same – of excruciating, agonising pain caused by the neurotoxins.
Apparently lionfish and scorpionfish venom is every bit as painful as that of stonefish. I suspect the reason stonefish are more deadly is simply that their spines and glands are much fatter, and inject larger quantities of poison.
With stonefish stings deaths have been recorded, and recovery from a non-fatal sting may take months, leaving permanent tissue damage.
The purpose of the toxin is to force potential predators to be overwhelmingly shocked by the agony of trying to bite, swallow or sit on the scorpionfish, and to either die or leave such fish well alone in future. Raising the dorsal spines, a posture beloved by photographers, is a threat, a warning, a preparation against a potential attack.
In my young and foolish days in the Caribbean I inadvertently played with fire. One of our dive-sites had a huge resident scorpionfish. So extremely relaxed was he that I tickled his chin and had him sitting on my hand. At the time I didn’t know that the pelvic fins he was resting on also carried toxic spines.
I didn’t get stung, but I wince at the memory. Not only did I deserve a nasty sting, but approaching any animal that close is an ignorant and negative way to dive.

CORAL REEFS ARE A SUPERB foraging ground for camouflaged, lie-in-wait predators. Nowhere else on Earth do so many small fish seek shelter in the reef structure and so inadvertently offer themselves as prey.
Stonefish and “regular” scorpionfish simply sit still, look like reef and wait for prey to move into slurp range, while lionfish are simply scorpionfish with large, fluttery fins that spend their evenings hunting rather more actively, sometimes herding and corralling prey ahead of them into the “slurp zone” by fanning out their fins.
At some point in the past 20 years, lionfish were accidentally introduced to Florida’s seas. This Indo-Pacific group had no natural enemies in the Atlantic and Caribbean, and have become a rather successful invasive species.
In the past few years particularly they have spread through the Caribbean, as far north as New York and as far across as the Azores, and possibly the Mediterranean. Large grouper and other potential predators have been largely fished out of these areas, so there seems to be little to stop the spread of lionfish.
We know the reef scorpionfish because reefs are where most diving takes place, but numbers of individuals are relatively low, and members of the scorpionfish group are far more abundant and successful in temperate and polar reefs, particularly in the northern hemisphere.
Dozens of species of sculpin dominate rocky and kelp reefs, particularly in the North Pacific. Many resemble scorpionfish, normally without such camouflage, but the most abundant group, the rockfish, are more grouper-like in appearance and habits.
Redfish are deepwater rockfish that shoal in huge numbers in deep, cold seas, and are probably the most successful scorpionfish of all.
A bizarre offshoot is the lumpsucker family, found all around the cold waters of the northern hemisphere.

THE MOST IMPRESSIVE of the scorpionfish group are found in the cold North Pacific. Diving off Vancouver Island, I came across a few ling-cod, the biggest well over a metre long, sitting on rocks waiting for a meal – a huge, smooth, somewhat sleek and poorly camouflaged scorpionfish.
The ling-cod, sablefish and skilfish have all been recorded as big as an adult human, and are generalist reef predators of almost anything slow enough for them to catch and small enough to fit into their cavernous mouths.
They fill niches similar to those that large “true” cod used to fill, and look more like cod than what we think of as scorpionfish.
Still, the heavy plated cheeks, the broad fan pectorals and the hefty build give clues that these are cousins to the photographers’ friend, the humble, strangely beautiful reef scorpionfish.