AdvancedPeacefulReef Safe with CautionIUCN: Least Concern
Yellow Boxfish
Ostracion cubicus
Family: Ostraciidae · Boxfish & Cowfish
Also known as: Cubicus Boxfish, Cube Boxfish, Polka Dot Boxfish
(c) Richard Hasegawa, some rights reserved (CC BY-NC)
Max Size
18"
Min Tank
125 gal
Lifespan
8-15 years
Origin
Indo-Pacific, Red Sea
Diet
Omnivore
Swims
Middle
Did You Know?
- Mercedes-Benz designed a concept car inspired by the Yellow Boxfish's hydrodynamic box shape
- Despite their rigid body, they are surprisingly maneuverable, using their pectoral fins like tiny propellers
- The ostracitoxin they release is so potent it can kill fish many times their size within minutes
About
The Yellow Boxfish is one of the most recognizable fish in the ocean, featuring a distinctive cube-shaped body covered in bright yellow coloration with dark polka dots as a juvenile. As they mature, adults become olive to blue-gray with faded spots, making them less visually striking but equally fascinating.
This species belongs to the family Ostraciidae, whose members have fused bony plates forming a rigid box-like carapace. When severely stressed, injured, or dying, Yellow Boxfish can release ostracitoxin, a potent poison that can kill other fish in the same aquarium. This defense mechanism makes them a risky choice for community tanks.
Despite the risks, many experienced aquarists successfully keep Yellow Boxfish by providing a calm, stable environment free from aggressive tankmates. They are slow swimmers with endearing personalities, often begging for food and recognizing their owners. A minimum of 125 gallons is needed for adults, as they can reach 18 inches in the wild, though typically stay smaller in captivity.
Feeding & Diet
Omnivore
An omnivore that feeds on algae, sponges, small crustaceans, and worms in the wild. In captivity, offer a varied diet of frozen mysis shrimp, brine shrimp, marine algae, spirulina, and small pellets. Feed 2-3 times daily in small portions. They are slow eaters and may be outcompeted by faster tankmates.
Compatibility
toxin-riskslow-swimmerpeacefulsensitive
Yellow Boxfish must be kept with calm, peaceful tankmates only. Aggressive fish will stress the boxfish, potentially triggering a fatal toxin release. Never house with triggerfish, aggressive wrasses, or territorial damsels. Compatible with peaceful community fish in large, stable aquariums.
Check CompatibilityBreeding
Not bred in captivity
Yellow Boxfish are pelagic spawners. Captive breeding has not been achieved. Males maintain small harems in the wild and spawn at dusk by rising in the water column to release eggs and sperm.
Special Requirements
- CRITICAL: Can release deadly ostracitoxin when stressed, killing all tank inhabitants
- Must be kept in a calm environment free from aggressive tankmates
- Slow swimmer — ensure it can access food without competition
- Cannot be kept with aggressive or overly boisterous fish
- Have activated carbon and a backup plan ready in case of toxin release
Water Parameters
Temperature72–78°F
Specific Gravity1.02–1.025 sg
pH8.1–8.4
Alkalinity8–12 dKH
Coloration
yellowblack spotsolive (adult)
Tags
toxin-riskslow-swimmerpeacefulsensitive
