Clumsy and adorable
Trunkfish, belonging to the family Ostraciidae, are the boxy delights that can make any diver’s day. Their blockish appearance and clumsy movements have wooed the hearts of many an admirer. Their eye-catching appearance and cutely curious behaviours often see them fawned over by new and experienced divers alike, but how much do we really know about them?
Eggs to boxes - the life cycle
When a mama trunkfish and a papa trunkfish love each other very much, the male trunkfish will perform a mating dance for the female. He will rhythmically move his fins and display his colours at her in his hopes of seduction. Once the mating is successful, the female will lay their fertilised eggs in a water column with a small oil bubble, where they float to the surface. These buoyant eggs are unprotected from predators until they hatch.
Once hatched, the baby trunkfish begins life in a stressful planktonic larval stage. They are transparent at this stage, and utterly at the mercy of ocean currents. It takes about a week before it grows into its juvenile stage and can begin to form its iconic bony carapace. They are absolutely adorable in this juvenile stage, with a tiny spherical body which can be as small as a pea and a shy behaviour in which they may occasionally peek around corners to watch for upcoming predators. They tend to elongate as they grow older, and reach sexual maturity after a few years.
Eat and being eaten - predation and prey
The trunkfish is a joy to watch hunt. Their chonky size, slow movements and tendency to hover over the ground seem somewhat reminiscent of a 50s scifi flying saucer. They roam the ocean floor, occasionally pausing to huff, puff, and blow into the sand to reveal its prey. It’s not above chipping away at coral with its mouth to find hidden morsels either. Its prey can range from tiny molluscs to crustaceans and worms, with a side dish of sponges. Food fit for a king.
Unfortunately, life isn’t just one long buffet for our stumpy friends. Groupers, barracudas and sharks are only some of the deadly dangers they have to deal with, and they don’t really have the agility to make the same quick escapes that other fish are capable of (though they can use their tail to accelerate away with surprising speed when they need it). Ultimately, the trunkfish has developed two very interesting defence mechanisms: the famous bony carapace and a lesser-known poison deployment system.
Suit up - armoured and ready for action
The trunkfish’s most visible and famous defence is its armoured carapace. The armour consists of dermal scutes with a highly mineralized surface plate lying over collagen fibres. The surface plates are formed primarily from hydroxyapatite, a calcium mineral formation similar to that found in our teeth. They are generally hexagonal, and have raised struts near the middle extending to the edges to provide structural integrity. These plates provide the bulk of the armoured protection.
Beneath the plates weaves a network of collagen fibres which thread together in ladder-like formations. It is suspected that this collagen network allows the trunkfish to better adapt to depth changes in the ocean, or perhaps they allow the fish to grow without needing to moult their armour.
Overall, the complex structure of the trunkfish’s carapace allows it to withstand impressive amounts of damage when attacked by predators, whether they are aiming to pierce through it with teeth or otherwise try and crush the trunkfish.
Chemical warfare - a toxic influence
The second defence mechanism of the trunkfish - poison - is less well known to your average diver and for good reason. It's not nearly as visible as the bony carapace, and it has no effect on humans… Usually. Just don’t go around drinking the stuff. When agitated, the trunkfish will excrete a substance called pahutoxin (previously known as Ostracitoxin after the trunkfish family, Ostraciidae) from specialised club cells beneath their skin. The highest concentration of these special cells is found near their mouth.
The pahutoxin is a deadly poison to other fish and marine animals. It is unusual as it is a non-protein toxin, something of a rarity in the underwater world. It is hemolytic, which means it causes any affected animal’s blood cells to rupture. One trunkfish is enough to kill a nurse shark should they mistake one for a tasty snack. The best part? The trunkfish doesn’t even have to be eaten for the poison to work. Once the poison is secreted, it is enough to affect and kill the surrounding marine animals. Luckily, the trunkfish itself is resistant to its own toxins.
Wrapping it up
Whether you like them for their unusual appearance or you just enjoy their odd swimming styles, I hope you have a newfound appreciation for our friends the trunkfish. I know I do! From an action-packed youth to fascinating defences in adulthood, the trunkfish is just one of those fish that just get more interesting the more you learn about them.
A very special thank you to Everett Turner Jr for sharing his amazing trunkfish photos!
