Published in Divelog Australasia August 2023

by Nigel Marsh

I saw my first boxfish underwater around fifty years ago, and from that very first encounter I was fascinated by these box-shaped fish. Over the years since I have seen thousands of boxfishes, and I still get a thrill every time I see one. I especially love juvenile boxfish, those cute little cubes with fluttering fins, and I can never resist photographing every single one I see. While they are extremely cute, boxfishes are also one of the more interesting fish that a diver can encounter.

Boxfishes got their rather appropriate name because of their box-like shape. However, this box shape varies considerably, with some square, others round or oval and some even have a triangular shape. Within the family they also have different names, with ones with horns called cowfish and triangular shaped ones called trunkfish.

While boxfishes vary in shape, they share a host of similar features. For a start they lack traditional scales, instead having a hard external skin created by fused scales, that forms a type of armour plating. This hard skin covers a rigid box-like frame, called a carapace, which has holes for the fins, mouth, eyes and tail. Because of their solid shape and small fins, boxfishes are quite slow swimmers, relying on their armour plating to kept them safe from harm. Predators that are silly enough to attack one quickly discover that boxfish have another secret weapon - toxic skin.


Boxfish are closely related to pufferfish and like their cousins they have toxins. These toxins are located in the skin and are released when the fish is under stress, like when being attacked. This toxin can kill other fish, and is a reason that boxfish are not normally kept in aquariums. It is also harmful to humans, so never touch or eat a boxfish.

Most boxfishes are brightly coloured and have skin pattern of spots, stripes or honeycomb shapes. Juvenile boxfish generally have a different colour pattern, and often a different body shape, to the adults. And most adult males have more colourful patterns than the females. Many boxfishes live in shallow water, and are regularly encountered by divers. However, some species are very shy and stay hidden from divers, while a few species live in very deep water, beyond the range of even tech divers.

Boxfishes are diurnal and mostly observed slowly wondering across the bottom looking for food. They feed on a variety of foods, including crustaceans, worms, small fish, molluscs, sponges, soft corals, tunicates and algae. Most boxfishes reside on coral reefs or rocky reefs, but some prefer mucky habitats of estuaries and bays. They feed amongst corals, rocks, seagrasses, kelp and on the sand, and some species blow away sand with jets of water to uncover prey. At night they find a safe place to hide and sleep.

Little is known about the behaviour and biology of most boxfishes. However, studies of the more common species have found the male has a harem of females, that can number up to four, and he defends his females and territory from rival males. When ready to reproduce, some males intensify in colour. Most boxfishes seem to reproduce in the late afternoon or at sunset, with the male and female rising into the water column to release their eggs and sperm. The larvae boxfish then drift with ocean currents as plankton until they grow large enough to settle on a new home territory.



There are two families of boxfish, the tropical boxfishes (Ostraciidae) and the temperate boxfishes (Aracanidae). The tropical boxfishes are also known as the true boxfish. This family contains 23 species that are found in tropical to warm temperate waters around the planet. They differ from the temperate boxfishes in having a more solid carapace, with separate openings for every fin, and rigid gills. The body shape of tropical boxfishes are more angular, with sharper ridges and keels giving them a more box-like form. The members of this family also have their mouth positioned lower, with more pronounced, puckered lips. The cowfish within this family also have longer and sharper spines, with horn-like projections on the head and body. Some members of this family have different colours for adult males and females, but others are almost identical.

The temperate boxfishes are more primitive, with most having a round or oval carapace with fewer holes for fins and a mouth positioned central on the head. The 12 species in this family are only found in the Indo-West Pacific region, with nine of them only found in Australia. Most species live in deep water, but fortunately for us a few Australian species are also found in the shallows. The temperate boxfishes have distinct colour differences between the male and female, both have pretty patterns, though some male cowfish species have outlandish psychedelic colours. Temperate cowfishes also have small horns, with some little more than skin folds.


Divers in Australia are very fortunate that they can see boxfishes in both tropical and temperate seas around the nation. Twenty species of boxfishes are found around Australia, though not all are seen by divers, as a number are only found in deep water and a few are very secretive. The following are some of the tropical and temperate boxfishes that divers can see in waters around Australia.


The wide-ranging Yellow Boxfish (Ostracion cubicus) is easily the most common boxfish seen by divers in Australia. This tropical species also ranges into temperate waters off New South Wales and Western Australia. The Yellow Boxfish gets quite large, reaching a length of 45cm. Juvenile Yellow Boxfish are bright yellow with black, and sometimes white, spots. As they grow their colours fade and dull, with the adults a bluish-yellow colour with black spots mostly on the back. Juvenile Yellow Boxfish are very common on tropical and subtropical reefs, but encounters with adults are uncommon.



The pretty Black Boxfish (Ostracion meleagris) is another tropical species that ranges into temperate waters off New South Wales. This species grows to 25cm in length and has different colour patterns for males, females and juveniles. The females and juveniles have the same colouration of black with white spots. While the male Black Boxfish has the same pattern on its back, and is a lovely blue with yellow spots on its head and sides. Researchers have discovered that the Black Boxfish makes humming noises when they spawn, the males also make other sounds when fighting over females or territory. The Black Boxfish is uncommon, I have only seen a few on the Great Barrier Reef and also on the reefs off southern Queensland.



The Striped Boxfish (Ostracion solorensis) is a shy species that is only found in warm tropical waters, mostly on the northern Great Barrier Reef. It is also one of the smaller members of the family, only growing to 11cm long. The Striped Boxfish is another species with different colours for males and females. The males are dark blue in colour with light blue spots and wavy lines, while the females and juveniles are yellow with black spots, blotches and lines. The Striped Boxfish is quite a shy species that likes to hidden under ledges.



The Horn-nose Boxfish (Ostracion rhinorhynchos) is a rarely seen tropical boxfish that is mostly found in Southeast Asia. This species is also found in Australia, but mainly in areas that few divers venture, the Northern Territory and northern Western Australia. The Horn-nose Boxfish grows to 35cm long and is a white-creamy colour with darker spots and a brown honeycomb pattern. This species has a strange lump on its face that looks like an over-sized nose.



The Thornback Cowfish (Lactoria fornasini) is a tropical species found throughout the Indo-Pacific region. These cute fish are a yellow or brown colour with a covering of blue spots, lines and dashes. The Thornback Cowfish has short spines, and grows to 20cm long. Though a tropical species, they are mostly found in New South Wales as they have a preference for mucky habitats, like Port Stephens and Sydney Harbour.


The spines of the Longhorn Cowfish (Lactoria cornuta) are quite long and project from the head and rear of their carapace. This is another tropical species found in the Indo-West Pacific region. They are reported to grow to 50cm in length, but ones that big are rare. The adult Longhorn Cowfish is a yellow to brown colour with large blue spots, while the juveniles are a grey colour with white spots. This is another boxfish that is mostly found in mucky habitats, and in Australia divers have encountered them at dive sites off Southern Queensland and New South Wales.



One of the strangest members of the boxfish family is the triangular-shaped Humpback Turretfish (Tetrosomus gibbosus). This species is a cream to brown colour with a pattern of darker hexagonal shapes and blotches. The Humpback Turretfish also has short spines and grows to 22cm long. This species is found in tropical waters throughout the Indo-West Pacific. I have never seen one of these weird fish in Australia, but have seen a few at muck sites in Indonesia and the Philippines.



Common throughout New South Wales, Eastern Smooth Boxfish (Anoplocapros inermis) is a temperate boxfish with a rounded carapace. Growing to 35cm long, this species has different colours for males, females and juveniles. The juveniles are almost perfectly round orange balls with darker spots, while the females are a pale yellow with brown blotches. The males change colour as they mature, losing their spots and becoming a pale blue and yellow colour.



The Western Smooth Boxfish (Anoplocapros amygdaloides) is very similar to its eastern cousin, but only found off southern Western Australia and South Australia. This temperate boxfish grows to 30cm long and has similar colour patterns to the Eastern Smooth Boxfish, but the females and juveniles have less spots and blotches. The adult males are blue with brown blotches. Juvenile Western Smooth Boxfish are more commonly seen by divers, as the adults tend to move into deeper water.



One of my favourite temperate boxfishes is the pretty Whitebarred Boxfish (Anoplocapros lenticularis). This species grows to 33cm long and is also called the Humpback Boxfish, due to the high ridge on its back. Juvenile Whitebarred Boxfish are round and coloured orange with darker spots and blotches. The adult females are orange with white and brown patterns, while the adult males are bright orange with white bands. The Whitebarred Boxfish is found off southern Western Australia, South Australia and also into parts of Victoria.



One of the most colourful fish of Australia’s southern reef is the lovely Shaw's Cowfish (Aracana aurita). This temperate boxfish is found from southern Western Australia to southern New South Wales and grows to 25cm long. The Shaw’s Cowfish is a common reef fish on rocky reefs, and is also found in estuaries and bays. The females, which are cream coloured with brown stripes, are more commonly seen searching the bottom for food, often in small groups. The shier males are less commonly seen and have a dazzling colour pattern of yellow and blue spots and lines. I once found a female Shaw’s Cowfish wedged in a ledge, trapped by its own horns. Fortunately, I was able to assist this poor fish to get free.



The Ornate Cowfish (Aracana ornate) is easily confused with the Shaw’s Cowfish, but has different patterns and its much smaller, only growing to 15cm long. The male Ornate Cowfish has a dense pattern of blue spots that are ringed with a darker border covering a yellow base. They also have blue lines on the face, tail and belly. While the female is a brown colour with yellow stripes that form circular patterns. Reported to occur from southern New South Wales to southern Western Australia, the Ornate Cowfish is mostly seen off Victoria and South Australia. Male and female Ornate Cowfish are often found under jetties, slowing moving across the bottom looking for food.


Boxfish are some of the most colourful and interesting fish that divers can encounter and Australia is blessed with a great variety of these fascinating fishes.