What on a muck site can hurt a diver.
This page gathers the 179 species, out of 971 in the index, whose entries include a hazard note. Each note gives how the injury happens, how serious it is, and a single sentence on what that means on the bottom. The most severe come first.
Muck diving is done close to the bottom. The animals are on the sand or buried in it, a macro frame is taken from a few centimetres, and a hand or a fin tip usually rests somewhere to hold the camera still.
Most of the animals listed below cause harm only through contact, when one is handled, lifted or leant on. A scorpionfish lying on the silt does not move towards anyone, and the risk is to whichever hand or knee comes down on it. Urchins, bristle worms, sea slugs with skin that is toxic to handle, and most fish with venomous spines follow the same pattern.
A few are not in that category. The animals in the first section can produce an injury that is life-threatening rather than painful, and some of them are cryptic enough that the contact is accidental rather than deliberate — a stonefish sitting in the sand is the standing example. Others in that section are only dangerous in the hand, which is a narrower risk but not a smaller injury.
Each entry takes its severity and mechanism from a fixed list of terms instead of a description written for that animal alone. A given injury therefore reads identically wherever it appears, and the index offers a severity filter. The last section of this page defines each term.
The page gives no first aid. Each entry names the mechanism and goes no further, because treatment should come from a doctor or a local hyperbaric unit.
Medical emergency 8
Photographed first, then commonestThe injured person must leave the water and reach medical care at once.
The snake is placid and bites almost only when it is handled or trapped, but its venom is a potent neurotoxin, and any bite is a medical emergency that requires antivenom.
Tetrodotoxin in the saliva has no antivenom. The bite is small and frequently painless, and the blue rings appear only when the animal is cornered or handled.
Each of the thirteen dorsal spines has a pair of venom glands. The fish defends itself by keeping still, so it does not move aside for a knee or a hand.
Nematocysts line the trailing tentacles. The venom of the larger species can stop the heart in minutes, and the smaller species produce a delayed syndrome affecting the whole body, so every cubozoan sting is treated as a medical emergency.
The venomous harpoon sits on a proboscis that can reach every part of the shell, the end a hand would grip included. Fish-eating species have venom that has caused deaths.
Saxitoxin and tetrodotoxin are present in the flesh and shell, survive cooking, and have caused deaths among people who ate the crab. A diver who only looks at it is at no risk.
The snake is venomous and a bite needs antivenom. It inspects divers at close range, and it should be allowed to do this without being pushed away or grabbed.
Its dorsal spines deliver the most potent venom known in any fish when it is stood or leant on. It does not flee, because its whole defence depends on not being seen.
Needs treatment 61
Photographed first, then commonestA doctor should examine the injury.
Venomous spines
37
Venom is carried in the thirteen dorsal spines and in the pelvic and anal spines. The fish stays where it is instead of swimming off, so a sting results from touching a fish that is not moving.
Venom is carried in the first dorsal spine and both pectoral spines. Under a light the ball of juveniles stays together, so it is photographed and not broken up.
The dorsal, pelvic and anal spines are venomous. It does not move away from divers, so the thing to track is where it has drifted.
The venomous dorsal spines run along the raised sail, and the sail is the part of the fish that a diver is most likely to brush.
The dorsal spines carry venom, and against encrusted rock the fish is very difficult to see.
Its spines are venomous, and the small pincer-like pedicellariae between them inject further venom. Among urchins, it is the one a fin most needs to stay away from.
The dorsal spines are venomous, and the fish stays still and allows divers to come very close.
Venom is carried in the dorsal, pelvic and anal spines. At night it approaches lights, so it may end up nearer to a diver than where it started.
A large fish that stays completely still against rock, with venomous dorsal spines. Injuries are caused by knees and hands, not by the fish.
The long spines are venomous and snap off inside a wound. Punctures heal slowly and tend to become infected.
Like the rest of the family it has venomous dorsal spines. Because it stays where it is as a diver approaches, stings come from a knee or hand placed on the sand and not from the fish itself.
A fish lying partly buried in sand is easily missed, so a hand or knee can land on it, and its spines are venomous.
Venom is carried in the dorsal, pelvic and anal spines. Resting on open mud, the fish does not move away when a knee or hand is placed beside it.
The dorsal spines are venomous. It walks instead of swimming and does not move off, so the risk is a hand placed next to it.
Venomous spines sit above the pectoral fins. Buried with only the mouth and eyes exposed, it is stepped on more often than it is noticed.
The fish lies buried in soft sediment, has venomous dorsal spines, and walks away from a hand instead of swimming.
The dorsal spines carry venom. A small, cryptic fish, and not one that is dangerous to approach.
A relative of the stonefish with venomous dorsal spines. It lies partly buried on open sand, where people come across it by accident.
Its dorsal spines are venomous, as in every scorpionfish.
Venom is carried in the dorsal, pelvic and anal spines. Sitting in weed, it stays where it is when a diver approaches, so any sting comes from a knee or hand, not from the fish.
The dorsal spines are venomous, and the fringed outline that hides the fish also means a hand can easily come down on it.
Like every member of the family it has venomous dorsal spines. It does not move when a diver comes close, so a sting results from a hand or knee placed on the sand, not from any movement by the fish.
Venom is carried in the dorsal, pelvic and anal spines. The fish stays put beneath a ledge instead of leaving, so stings come from a motionless fish in a tight space.
The dorsal spines are venomous, and the fish tends to drift into objects instead of swimming away from them.
The dorsal spines are venomous. The fish stays still when approached and is very difficult to distinguish from rubble.
The venomous dorsal spines extend along the whole raised sail, which is the part of this motionless, drifting fish that a diver is most likely to touch.
The first dorsal fin and both pectoral fins carry serrated venomous spines. It feeds pressed against sand and structure, so contact usually comes from a knee or hand on the bottom, not from a fish in midwater.
The fish lies buried, carries venomous dorsal spines and does not move off. Most injuries happen when weight is placed on sand that looked empty.
The dorsal, pelvic and anal spines carry venom. Since the fish stays where it is when approached, contact depends on where a camera port or a hand is placed.
The fish is well camouflaged and motionless on the surface of the sediment, where a knee or hand may come down on its venomous dorsal spines.
The fish lies buried in soft sediment with venomous dorsal spines, and injuries usually come from kneeling on it or placing a hand on it.
Like all its family it has venomous dorsal spines. It stays where it is on rubble instead of leaving, so contact comes from a fin or hand placed on a bottom that appears empty.
The dorsal spines are venomous, and the fish stays pressed against the roof of a ledge instead of leaving.
Like the whole scorpionfish family, it has venomous dorsal spines.
It has venomous dorsal spines and spends daylight hours buried in silt.
Bite
10
Moray bites crush, tear and readily become infected. The constantly opening jaw is for breathing and is not a threat, but a hand near the hole is still at risk.
The teeth are long and fine, and the eel tends to shift position instead of pulling back. A bite crushes tissue and easily becomes infected.
Its teeth are blunt and crushing, not fang-like, yet a bite still breaks the skin and becomes infected. It hunts in very shallow water where people wade.
The animal strikes upward out of its burrow at anything that passes above, and its jaws shut with enough force to cut.
Bites are uncommon and almost always follow an obvious threat display. A shark that arches its back and lowers its pectoral fins is signalling a diver to move away.
A big moray bites hard, and the wound tears and readily becomes infected. Bites occur when the eel is hand-fed or a hand is pushed into a crevice.
A nesting fish guards a cone of water rising above the nest and will rush in and bite, removing a piece of flesh. The accepted advice is to leave the nest horizontally, not by swimming upward.
The bite of a large moray crushes, tears and readily becomes infected. Almost all recorded bites involve feeding the fish or a hand pushed into a hole.
Its long teeth point backward, and a limb once bitten is difficult to release. Bites follow standing on the shark or placing a fin or hand in front of its head.
A moray of this size may bite hard at a hand brought near its hole, and eating it has been linked to reported cases of ciguatera poisoning.
Venomous sting
5
Near the tip of the tail sit one or two venomous spines. A ray stings when it is trapped, handled or stood on, and the result is intense pain and a wound that must be cleaned.
The tail carries a serrated venomous barb that is thrust upward and backward in defence. Nearly all injuries come from stepping on a ray buried in shallow water.
The tail base carries one or two long venomous spines. Stings follow when a buried ray is stepped on or a diver settles onto it, and the wound is deep and very painful.
The flower-shaped pedicellariae are venomous pincers that grip the skin, break away and keep injecting. Touching any part of the animal delivers venom, and the pain is severe.
Venomous spines sit at the base of the tail and may be used in defence when the ray is handled or cornered. A ray swimming freely poses no risk.
Strike
4
Its calcified club strikes fast enough to break shells and crack a camera port, and it hits at any finger placed near the burrow.
A small smashing club, but one that moves as fast as that of its larger relative. It strikes at anything that enters the mouth of the burrow.
At speed, a large needlefish can leap clear of the water and impale a person. Injuries happen at night in connection with lights directed across the surface and are not linked to ordinary diving.
From the mouth of its burrow it fires barbed spearing appendages upward at anything that passes.
Electric shock
1
Paired electric organs in the disc discharge on contact, repeatedly if needed. The shock reaches anything that touches the ray, including a hand placed on sand where it lies buried.
Sharp spines
1
The spines are brittle and barbed and break off inside the wound. They carry no venom, but the fragments cause trouble far beyond the size of the injury.
Stinging cells
1It lies on open sand at the height of a knee or a hose, and its nematocysts cause burning welts and blisters that may persist for weeks.
Toxic if eaten
1
It is the most frequent cause of ciguatera poisoning in the region, large fish above all. In the water it is harmless.
Venomous bite
1
Every octopus is venomous, and this species is often confused with the blue-ringed octopus. Its venom has not been characterised, which calls for caution and offers no reassurance.
Caution 110
Photographed first, then commonestPainful, but usually needs nothing beyond cleaning the wound and waiting.
Toxic to handle
30
When handled or stressed the fish releases grammistin, a bitter toxin in its skin mucus. A glove gives protection, but the fish should not be touched with bare hands and should not be eaten.
Its skin secretes compounds derived from sponges, which divers usually discover after handling one and then touching the face or mask.
A predator-repelling toxin seeps from pores at the base of the dorsal and anal fins. It irritates eyes and skin, so a diver who handles the fish and then clears a mask is likely to suffer for it.
When handled, several Pleurobranchus species secrete strongly acidic mucus from the skin. It is unpleasant, not dangerous, and easily avoided.
Under stress its skin releases a bitter toxin into the water that can kill other fish nearby. A diver who does not handle it is not at risk.
Saponins in the body wall are released into the water when the animal is damaged or under heavy stress. They irritate on contact; they do not sting.
Sponge-derived compounds are secreted through the skin, and a large animal produces a large amount. The residue passes to gloves and from gloves to anything they touch.
If harassed it can release a skin toxin into the water around it, so it is watched from a distance and not crowded.
Handling makes it expel sticky Cuvierian tubules, which cling to skin and equipment and contain an irritant.
The body wall contains holothurin and the Cuvierian tubules are very sticky. Both irritate the skin, and in the eyes they are much more painful.
Compounds derived from sponges are secreted through the skin. People learn this by handling one and then touching the face or mask.
Some species expel sticky Cuvierian tubules, others give off a red fluid containing holothurin, and both irritate the eyes and skin.
Handling causes it to release purple ink and a separate white secretion. Each one irritates, and experiments show the white secretion deters predators by chemical means.
Compounds derived from sponges are secreted through its skin, and they are toxic enough to kill fish kept in a confined space with it.
Some Palythoa colonies contain palytoxin, which enters through broken skin and the eyes and does not act by stinging. How much a colony holds varies greatly from one to the next.
Stress or handling causes the skin to release a toxin. This threatens other animals in a confined space more than it threatens a diver, but the fish should still not be picked up.
Sponge-derived compounds leave the skin as a secretion, and fingers carry them on to a mask seal or an eye.
Compounds derived from sponges are held in the skin, and if the animal is confined or handled it lets them out into the water around it.
It accumulates toxins from the cyanobacteria it feeds on, and the same compounds irritate the skin of anyone who touches the mats.
Under severe stress the skin releases a toxin, a response recorded mostly in captivity. A diver will not provoke it.
The tissue contains defensive compounds, which is what lets so soft an animal travel in daylight.
When handled it gives off purple ink and, separately, an opaline secretion. Both act as chemical deterrents and either can irritate the skin and eyes.
Compounds taken from sponges are secreted through its skin. Nothing is gained by picking one up.
Its skin secretes compounds derived from sponges. People usually discover this by handling one and then touching the face or mask.
Defensive compounds are held in its tissue and papillae, which explains how such a soft and conspicuous animal can travel in daylight.
Grammistin, a bitter toxin in the skin mucus, is released when the fish is confined or handled. The toxin acts through contact and ingestion, not through a spine or a bite.
As a phyllidiid it has the skin secretions typical of the family. Looking at it is harmless; handling it is best avoided.
Like other boxfish it releases a skin toxin under severe stress, recorded mostly in captivity. A diver will not provoke it.
Its skin secretes compounds derived from sponges. These pass to the fingers, and from the fingers to an eye or a mask seal.
In some nemerteans the body mucus contains tetrodotoxin and related compounds. That is a sufficient reason not to handle a worm whose identity is unknown.
Stinging cells
21
The sting is mild: tentacle stinging cells irritate thin skin on contact.
Its tentacles grip hard and sting on contact. Of all the anemones, this is the one most likely to catch an arm resting on the sand or a bare hand.
Stinging cells in the tentacles irritate thin skin on contact. It is not a serious hazard, but it is a reason to keep camera ports and hands away.
The trailing arms, which sting on contact, reach much further than the bell, so a diver can be stung a metre from the visible bell. The sting hurts on bare skin but is not dangerous.
Stinging cells on the trailing tentacles can reach well beyond the visible body, so stings usually happen to divers who assumed the animal ended at the edge of the light. For the species seen on blackwater dives the sting is painful, not dangerous.
Like other aeolids that eat hydroids, it keeps the stinging cells of its prey in the tips of the cerata. It is very small and there is no reason to touch it.
The tips of the cerata hold stinging cells taken from its hydroid prey, which can discharge on contact. The animal is small and there is no reason to touch it.
Nematocysts cover the bell as well as the tentacles and oral arms, so contact with any part of the animal stings; the sting is painful and can mark the skin for days, but is not dangerous to a healthy adult.
Stinging cells taken from its hydroid prey are kept in the tips of the cerata and may discharge on contact. It is small, and there is no reason to handle it.
The long pink tentacles carry stinging cells along their whole length and can spread well beyond the float, so a photographer should keep clear of them.
Aeolids that feed on hydroids can keep the prey's stinging cells in the tips of their cerata. These slugs are tiny and there is no reason to handle them.
Males and young females rip tentacles from the Portuguese man o' war and hold them in their arms. The nematocysts on these borrowed tentacles remain active, so an octopus of this size is able to sting a bare hand.
The sting is an uncomfortable burning, not a dangerous one. Stinging cells sit on the mouth-arms and the filaments that hang from them, and also in the mucus the animal sheds into the water around it, so bare skin can be irritated without touching the arms.
Touching it gives an instant burning sting followed by a welt that may itch for days. The rinse is vinegar, not fresh water, and rubbing makes the reaction worse.
A light brush causes a burning welt lasting days. It most often happens on the wrists, the back of the neck and the strip of skin above a glove.
Stinging cells from the hydroids it feeds on are kept in its cerata, and these can discharge when the animal is touched.
The disc sticks firmly and stings on contact. On a bare hand the result is a burning welt, not a serious injury.
It stings on contact and also releases free-floating clusters of stinging cells into the surrounding water, which is why swimmers itch without having touched one.
The tips of its cerata store stinging cells obtained from hydroids. It is very small, and nothing is gained by handling it.
The tips of the cerata hold stinging cells taken from siphonophore prey. They fire on contact with skin and are concentrated to the point that the sting can be stronger than that of the siphonophore itself.
The stinging cells are carried on the mouth-arms, which hang well below the bell. The sting is described as mild and is not known to be dangerous, but bare skin brushed by the arms can still burn for some minutes.
Venomous spines
16
The long banded primary spines are blunt and largely harmless. The danger lies in the short dark secondary spines, which are fine, barbed and mildly venomous and snap off in the skin.
Venom in the dorsal, anal and pelvic spines causes an intensely painful sting lasting several hours. The fish is not aggressive; the risk comes from contact and handling.
The hinged blade at the tail base can cut to the bone, and its venom makes the wound much more painful than it looks. Handling the fish is the danger; swimming past it is not.
Venom in the dorsal, anal and pelvic spines causes a sting that hurts for several hours. The fish does not behave aggressively.
Venom in the dorsal, anal and pelvic spines causes a sting that hurts for several hours. The fish keeps away from divers, so the risk lies in handling one or in bumping into a fish wedged in at night.
A sharp venomous spine sits on the rear edge of the cheek. The risk comes from handling the fish or reaching blindly into a crevice, not from the fish's behaviour.
Each side of the tail base has a hinged blade that can open a deep cut, and the wound hurts more than its size would suggest. The risk comes from handling or netting the fish, not from swimming near it.
Members of this family have venomous dorsal spines, but this fish is small and the stings reported from it are mild.
Venom is carried in the dorsal, anal and pelvic spines. A sting to the hand is painful, while a diver who keeps clear of the fish is in no danger.
The long primary spines are blunter and do little harm. The short dark secondary spines are the problem: fine, barbed, mildly venomous, and liable to break off in the skin.
The lightest touch leaves hollow toxic bristles in the skin, and they cannot be brushed away. Burning and numbness follow and last for hours.
The hinged blade at the tail cuts easily, and the wound hurts far more than its size would suggest. Handling a trapped or netted fish is the risk; swimming beside one is not.
Venom is carried in the dorsal, anal and pelvic spines. The sting hurts but is not dangerous, and the fish poses no threat unless it is handled.
The dorsal and opercular spines are venomous. The fish lies wedged in rubble, so contact usually comes from a hand resting on a stone, not from a fish out in the open.
Venom is carried in the dorsal, anal and pelvic spines. It sits wedged into rubble instead of out in the open, so contact usually comes from a hand placed on a stone.
A small fish sitting deep in branching coral, with venomous spines on the dorsal fin and head. Contact usually comes from a hand steadying against the coral head, not from a fish in open water.
Bite
14
Fine recurved teeth line the jaws, and the fish strikes at anything of fish size that swims near. It ignores divers, but a hand placed on the sand next to one is within reach of that strike.
Bare skin may be bitten, leaving a small round nip. The bite startles more than it harms, and at some sites the same divers are bitten again and again.
It has the teeth of a moray, but it remains in its hole and bites only what enters it.
So little of the animal is visible that the realistic risk is treading on or grabbing the buried head, which provokes a bite.
An ambush predator with a strong strike, it lunges upward out of the sand; a knee or hand put down on the buried head can receive a hard bite.
The teeth are blunt and crushing, not fangs, so a bite holds on instead of tearing, but it still breaks skin and becomes infected. Bites are caused by a hand pushed into a hole.
It bites upward at anything that moves over its head, so look at the sand before putting a hand or knee down.
A nesting or territorial fish may approach and bite. Its teeth are smaller than a titan triggerfish's, but it commits to an attack more quickly.
A fish guarding a nest in shallow sand will rush at a diver and may bite. It defends only a small area, and moving a few metres to the side ends the encounter.
A fish guarding a nest defends the water column above it and may bite. Nest encounters with this species happen far less often than with the titan triggerfish.
This species, unlike other brittle stars, has jaws strong enough to grip skin. The bite causes no real harm but is a true bite.
Living inside rubble, this eel may have its head at the entrance of a gap that appears empty, and it bites in defence. Its teeth crush rather than cut.
It strikes upward out of the sand at anything that passes near, so a hand or knee placed without looking risks landing on a buried head.
A moray bite tears and easily becomes infected. This small species keeps to the inside of rubble, so the only risk is to a hand pushed into a hole.
Toxic if eaten
14
Highly toxic as food, but harmless in the water unless a diver handles it.
Tetrodotoxin, with no antidote, is present in the skin and internal organs. It is no hazard while diving, but it is never eaten.
A toxin not found in any other cuttlefish tested is present in its muscle tissue. It is not a contact hazard and gives no reason to keep a greater distance than normal.
Tetrodotoxin, with no antidote, is present in the skin and organs. Divers are in no danger from the fish, which is dangerous only as food.
Tetrodotoxin is present in the skin and organs. In the water the fish is no risk.
Like other boxfish it can release a skin toxin under severe stress. It is no hazard while diving, but it is never eaten.
Under severe stress the skin releases ostracitoxin, recorded mostly in captivity. It is no hazard to a diver, but it is a real one to any animal confined in a bucket with it.
Like other tobies it carries tetrodotoxin and is dangerous to eat, but it is harmless to a diver who does not handle it.
Tetrodotoxin, with no antidote, is present in the flesh, skin and organs. It poses no danger in the water, although a handled fish can remove a finger's worth of skin with its fused beak.
Tetrodotoxin is present in the skin and organs. The fish is dangerous only if eaten and harmless in the water.
The caudal blade is sharp but carries no venom. Its flesh has been linked many times to ciguatera poisoning in the region.
Tetrodotoxin, for which no antidote exists, is present in the skin and organs. The danger is confined to eating the fish; in the water it is harmless.
Tetrodotoxin is present in the flesh, skin and viscera. The fish obtains it through its diet and does not produce it itself.
Like other boxfish it releases ostracitoxin from the skin under severe stress, a response recorded mostly in captivity and not in the sea.
Sharp spines
10
The tail base carries a sharp hinged blade. Handling a caught fish is where the risk lies.
On each side of the tail are two fixed blades, sharp enough for a deep cut. The risk arises when a caught fish is handled.
Each side of the tail has two fixed, forward-pointing blades that are sharp. The risk comes from handling a speared or netted fish, not from meeting one in the water.
Its stout spines have sharp points that pierce a knee or hand placed on them, and they can snap off beneath the skin.
Long, sharp, brittle spines snap off in the wound, so the injury causes trouble out of proportion to the animal's size.
The crab has sharp teeth along the sides of the carapace and strong claws, stands its ground, and grips without letting go.
Each side of the carapace ends in a long spine, and the slender claws can pinch through a glove. The crab stands its ground with claws raised.
Forward-pointing spines on the carapace and antennae tear skin. The lobster backs into shelter and does not advance.
Forward-pointing spines that tear skin cover the carapace and the bases of the antennae. The lobster backs into a hole and does not attack.
Sharp spines on the carapace and chelipeds tear skin. The lobster withdraws into its crevice and does not come out at anything.
Strike
2It fires a barbed spearing appendage at a hand pushed into its cavity. At this size the result is puncture wounds, not an injury that needs treatment.
The raptorial club is a smashing weapon, used against a finger or hand pushed into its cavity. At this size it causes a bruise or a split nail, not an injury that needs treatment.
Venomous bite
2
Its grooved fangs inject venom in defence if a predator or a hand grabs it. A diver who only watches the fish is not at risk.
Every octopus has a hard beak and venom. Bites are defensive and follow handling; the wound is small but still needs proper cleaning.
Venomous sting
1The spines are short and blunt. Between them sit small venomous pedicellariae that can cause a minor sting on bare skin.
The categories
Each mechanism term below is shown with the definition used across the site and a count of the entries that list it. One animal may list several, so the counts total more than 179.
- Venomous spines55
- Venom carried in spines on the fins or body. Nearly every injury comes from touching the animal, not from an attack by it.
- Venomous sting7
- A sting or barb on the tail, used in defence.
- Venomous bite6
- Venom injected through a beak or a bite.
- Stinging cells23
- Nematocysts that fire when they touch skin.
- Sharp spines16
- Spines that pierce the skin and snap off. There is no venom, but the wound heals slowly and often becomes infected.
- Strike6
- A raptorial appendage, either a club or a barbed spear, that strikes too fast for the eye to follow.
- Bite25
- A defensive bite that breaks the skin, usually after a hand has been placed too close.
- Toxic to handle31
- Irritant compounds carried in the mucus or skin.
- Toxic if eaten21
- Poses no danger to divers. Listed because this is often why the animal is left alone.
- Electric shock1
- A shock from paired electric organs, given on contact and able to be repeated.
Where they sit in the index
The full index of 971 species can be narrowed by severity, and also by group, destination and rarity. The glossary explains the words that appear in the notes.