If you’re a bit more of an experienced marine keeper and want a striking fish to add to your marine aquarium, this fun fish might be just what you’re looking for. The Hawaiian Boxfish (Ostracion meleagris) is an unusual looking fish, due largely to the fused hexagonal bony plates it uses to cover its more conventional skeleton, and its small, puckered mouth. However, the colouration of this relatively small fish (reaching between 10-18cm (4-7 inches)) is one of its main attributes. Both sexes exhibit spots across their entire body, but males are a bright, vivid blue whilst females are black, allowing easy differentiation between them. Hawaiian boxfish are omnivorous, feeding on clams, mussels and other invertebrates, and some coral species, so if you want to add them to your reef setup, make sure your corals haven’t made its ‘tasty’ list. When stressed, these fish will release a toxin as a defence mechanism called pahutoxin (formerly ostracitoxin), and this makes them an experienced keeper’s fish. This toxin is fascinating, unique to the boxfish family in the underwater world, and is a surfactant. The toxin (if it enters the bloodstream of a predatory fish) will break down the membranes surrounding red blood cells, preventing oxygenated blood from reaching the fish’s major organs and the predator effectively suffocates. In the open ocean, this has a small destructive capacity, as the toxin is quickly diluted to a non-harmful level. However, the volume of indoor aquariums is not large enough to dissipate the toxin quickly enough or widely enough for other tank-inhabitants to not be affected. If you are interested in keeping these fish, you must be extraordinarily careful, extremely vigilant and prepared for the worst-case scenario (if you plan to keep them with other species). Remember that even seemingly small changes can cause stress to fish, and this may set off the boxfish’s defence mechanisms. However, despite their bad rep, and if you are consistently careful, these will make very entertaining fish for your marine setup. They are a flashy, plucky little fish who really are a joy to watch.
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