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Interesting Facts about the Yellow Boxfish
[Phylum: Chordata] [Class: Actinopterygii] [Order: Tetraodontiformes] [Species: Ostracion cubicus]
There are many colourful boxfishes living in the wild and in captivity. Yet, the genus with a bright yellow boxy body and black spots is the one that gets most attention.
This page contains some lesser-known facts about yellow boxfish (Ostracion cubicus), including where they thrive best, what kind of food they eat, and how these box-shaped fish reproduce.
Ostracion cubicus Habitats and Distribution
The boxfish classification Actinopterygii is a saltwater fish that inhabits most tropical and subtropical oceans around the world.
However, the yellow boxfish family thrive better in several key regions, especially:
- Australia (western, northern, and south eastern coastlines)
- Indian Ocean (e.g. Indonesia dive sites, Thailand dive sites)
- Eastern Mediterranean (including most of the Red Sea dive sites)
- The Pacific Ocean (e.g. the Philippines, French Polynesia, Hawaii)
- Southeastern Atlantic Ocean (e.g. south coast of South Africa)
Yellow boxfish tend to inhabit shallow coral reef structures and sandy lagoons. Even so, the depth range for these cuboid creatures varies between a few metres and down to depths approaching 50 metres (165 feet).
Fun Fact: The box shaped body is not the most hydrodynamic of marine vertebrates. But, an agility for swimming and hovering comes from a clever combination of their tiny fins that perform a type of "rowing" maneuver.
Yellow Boxfish Characteristics
The "triangular" shape of their lemon coloured bony carapace is the primary feature used to identify the species.
They have a bony structure that encases most of the body and contains fused armoured scales. These offer them some protection against their main predators (e.g. groupers, moray eels, octopuses, and sharks).
The body colouration for the scaly hexagonal plate-like yellow skin pattern and black dots tend to be more vivid in juveniles.
Like most aposematic marine life, Ostracion cubicus can also mimic toxic nudibranch species to help them avoid capture.
Yellow Boxfish Size
The average size for fully matured yellow boxfish is forty five (45) centimetres long (18 inches).
Pro Tip: One of the biggest boxfish species is the scrawled cowfish (Acanthostracion quadricornis) which can grow up to fifty (50) centimetres long (20 inches). By comparison, the shortnose boxfish (Ostracion nasus) is one of the smallest and reaches a maximum length of thirty (30) centimetres.
Boxfish Toxin
The secretion of a toxic substance (ostracitoxin) by some species of boxfishes, including yellow coloured boxfish, is used to evade capture by potential predators when they feel stressed or threatened.
Hence, this defencive action is likely to impact other common home aquarium fish when kept in the same tank as a cubed boxfish.
What Do Yellow Boxfish Eat?
Being a typical omnivore means the boxfish species (Ostraciidae) are comfortable eating a healthy combination of animal and plant matter, including copepods and detritus.
Thus, you may see them hovering over a sandy ocean floor searching for small crustaceans, worms, sponges, krill and tunicates. They will also consume any green algae that grows on rocky slopes.
Pro Tip: The best scuba diving spots in Thailand to see yellow boxfish are the Surin Islands, Similan Islands, and the Tarutao National Marine Park near the coast of Satun Province.
Yellow Boxfish Reproduction
The average lifespan for most boxfish types is about four (4) years. However, compared with many other marine vertebrates, they have a slow reproductive rate.
They start broadcast spawning when the warm water arrives - usually towards the end of spring. After forming a group, usually one (1) male and up to four (4) females, they begin the mating ritual (dancing in small circles) near shallow reef structures.
Here's the thing:
Accurate information about the breeding habits of the boxfish species is generally limited. Even so, biologists have determined that females lay lots of eggs on a daily basis for about one month.
Following that, the male boxfish will release his sperm to fertilise the eggs as they float in the water column near the surface.
The tiny pelagic larvae drift in the open ocean and feed on plankton until they grow big enough to settle on a reef as juveniles.
Threats and Predators
The IUCN Red List of Threatened Species assessed the yellow boxfish (Ostracion cubicus) in 2023 and specified them as being of "Least Concern" (LC).
However, some of the contributing factors for a decline in certain vulnerable areas include certain types of human behaviour (e.g. coral reef destruction and degradation, overfishing, the aquarium trade, and warming seas).