Humu Rectangle Triggerfish (Rhinecanthus Rectangulus) saltwater aquarium fish

Overview:

The Humu Rectangle Triggerfish, likely referring to the Humu Humu (Rhinecanthus species), is a bold, highly active marine fish that requires a large, stable aquarium and careful planning. Despite its tough appearance, it is sensitive to poor water quality and stress. Ideal care begins with a spacious tank of at least 180 gallons for a single adult, with even larger systems preferred because this species grows strong, patrols territory, and can become aggressive if confined. Provide a secure lid, as triggerfish are powerful jumpers and may blast equipment or rearrange loose decor. Use abundant open swimming room balanced with sturdy rockwork, caves, and overhangs for shelter. Strong filtration, stable salinity, and excellent oxygenation are essential. Keep temperature around 74–80°F, salinity near natural reef levels, and maintain very low ammonia and nitrite.

Diet and Feeding:

Humu Rectangle Triggerfish are omnivorous predators with robust appetites and crushing teeth adapted for hard-shelled foods. Feed a varied marine diet including chopped shrimp, squid, clam, mussel, krill, marine pellets, and occasional algae-based foods or nori. Shell-on foods can help maintain natural jaw use and reduce boredom, but should be offered in moderation to avoid excessive fat intake. Feed adults once or twice daily, giving only what they consume quickly. Overfeeding is a common problem because triggerfish are eager eaters and can become obese, dirty the tank, and develop digestive issues. Soak foods in marine vitamins and fatty-acid supplements several times weekly to support color, immunity, and long-term vitality.

Compatibility:

This species is not a community fish in the usual sense. It is often aggressive, territorial, and may harass or kill smaller tankmates, especially fish that are timid, slow, ornate, or able to fit in its mouth. Suitable companions are limited to larger, assertive marine fish that can hold their own, such as some tangs, large wrasses, groupers, or other similarly robust species, but compatibility always depends on individual temperament and tank size. Avoid crustaceans, snails, urchins, and most decorative invertebrates, as triggerfish commonly view them as food. Introductions should be done with caution, ideally with the triggerfish added last after the tank is established and other residents have territory. Even then, close observation is necessary.

Health and Quarantine:

Common health issues include stress-related color loss, fin damage from aggression, nutritional imbalance, and bacterial infections from wounds. Because triggerfish are active and powerful, injuries from tankmates or sharp decor can become infected quickly. Quarantine all new arrivals for 4–6 weeks in a separate marine system to monitor appetite, breathing, skin condition, and feces. During quarantine, offer varied foods and treat only if symptoms appear, rather than medicating routinely. Maintain pristine water, stable temperature, and low stress, since this species can deteriorate quickly in poor conditions. Regular observation, strong filtration, and conservative stocking are the best preventive care.

algae/nori spirulina mysis brine shrimp
The Humu Rectangle Triggerfish is an active, bold swimmer that patrols the tank with short bursts of movement and needs ample open space along with sturdy rockwork and hiding spots to retreat into. It is semi-aggressive to territorial, especially as it matures, and is typically intolerant of conspecifics unless kept in a very large system with strong visual barriers and carefully planned spacing. A minimum tank size of about 180 gallons is recommended, with a layout that breaks lines of sight and provides secure caves to reduce dominance behavior and stress. In mixed communities, it generally coexists best with robust, similarly sized tank mates, but it is not considered reef-safe because it may harass fish and consume crustaceans, snails, and other invertebrates. Its diet is omnivorous with a strong carnivorous tendency, centered on meaty foods such as shrimp, squid, clams, krill, and quality marine preparations that support its natural hunting and crushing behavior.

FAQ

Frequently Asked Questions

About the Humu Rectangle Triggerfish

  • How large does a Humu Rectangle Triggerfish actually get in captivity, and what tank size is realistic long-term?
    Most adults reach about 10–12 inches, and they are powerful swimmers with a bulky body that needs horizontal room. For a long-term setup, 180 gallons is a practical minimum, with larger being better if it’s the main fish. Smaller tanks often lead to pacing, aggression, and poor behavior.
  • Is a Humu Rectangle Triggerfish reef-safe, or will it destroy a mixed reef?
    No, it is not reef-safe. It is a classic “flesh, shell, and rock rearranger” that will eat ornamental shrimp, crabs, snails, and small fish, and it may nip at corals or knock over aquascape. It is best kept in a fish-only or predator-style marine aquarium.
  • What should I feed a Humu Rectangle Triggerfish to keep its teeth healthy and prevent overgrown jaws?
    Feed a varied meaty diet with a strong shell component: frozen shrimp, squid, krill, clam, scallop, fish flesh, and occasional hard-shelled foods like crab legs, clams in shell, or snails. The hard items are important because triggerfish teeth continue growing and need wear. Feed 2–4 times per week for adults, more for juveniles.
  • Can Humu Rectangle Triggerfish be kept with other triggerfish or aggressive fish?
    Usually only with equal-sized, assertive tankmates in a very large aquarium. It is territorial and can become especially nasty toward other triggers, puffers, large wrasses, groupers, and slow-moving fish. Best companions are robust species that can hold their own and are introduced carefully, with plenty of space and rockwork breaks.
  • Why does my Humu Rectangle Triggerfish seem fine one day and suddenly act defensive or “bitey” near the tank?
    This species is highly aware of its environment and can become territorial around its den, especially as it matures or when it claims a cave. It may charge hands, snap at equipment, or defend a specific area of rockwork. This is normal triggerfish behavior, so use tongs, plan maintenance around its territory, and avoid cornering it in the tank.