Geometric Pygmy Hawkfish

The Geometric Pygmy Hawkfish (Xenanthias inermis) is recognizable by a pale body with red-orange angular blotches, large eyes, and an elongated dorsal spine. Its compact shape allows it to tuck between rocks and watch for passing prey. Older references may list it as Plectranthias inermis.

Indo-West Pacific is its native range. In the wild, it is associated with rubble and crevices at the base of coastal and inner reef slopes. It waits close to the rockwork and makes short strikes at small crustaceans and other prey.

This species is a small anthias-family perchlet commonly sold under a hawkfish trade name. In the aquarium, its behavior centers on rock perches and short feeding strikes. This perchlet spends much of its time perched in crevices. Arrange small ledges and place food where it can make a short strike from shelter.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 30 gallons
Adult Size: Up to 1.8 inches (4.5 cm, standard length)
Temperament: Semi-Aggressive
Diet: Carnivore
Reef Safe: With Caution
Region: Indo-West Pacific
Scientific Name: Xenanthias inermis

Tank Requirements

Provide at least 30 gallons for long-term adult housing. Plan for up to 1.8 inches (4.5 cm, standard length). Choose a footprint that leaves swimming or feeding space after the rockwork is in place. Provide enough bottom area for several distinct perches.

Use mature rockwork with short ledges and narrow crevices at several heights. Keep an open patch in front of the principal perches so the fish can strike at nearby food.

Maintain gentle current around the preferred perch and stronger circulation elsewhere. Place a small portion where it passes close enough for the fish to see and intercept it.

Secure the cover and the rockwork. Use a fitted lid with gaps around plumbing and cables closed. Leave enough clearance for routine maintenance, and anchor heavy structures so they remain stable if substrate shifts. Check that the fish can move between shelters without needing to pass another bottom dweller’s preferred perch.

Use an established biological filter, good surface agitation, and circulation that reaches behind the rocks. Arrange the display so you can siphon uneaten food from under ledges and service mechanical filtration easily. Distribute flow across the tank so one narrow jet does not become the only place food moves.

Include different perch heights so the fish can select a sheltered ledge or move closer to food. Keep a few openings along the lower rockwork clear of sand and coral growth. A carefully placed feeding tool can deliver a small meal near cover while more active fish are occupied elsewhere.

Diet and Feeding

The Geometric Pygmy Hawkfish is a small carnivore. It watches from cover and takes small animal prey within reach. Deliver food near its perch and size pieces so it can swallow them easily.

Offer a rotation of suitable foods.

• Small mysis shrimp
• Enriched brine shrimp
• Finely chopped marine shrimp
• Small marine carnivore preparations

Start with one or two small meals daily. Adjust the portion size to the amount swallowed, body condition, and the system’s ability to export waste. Observe a strike near the perch and confirm the food is swallowed.

Confirm feeding at each introduction. This perchlet spends much of its time perched in crevices. Arrange small ledges and place food where it can make a short strike from shelter. Newly arrived fish may take live or frozen food before accepting dry preparations. Keep portions small and offer a complete marine food as part of the rotation once the fish is eating reliably.

Watch for a pinched belly, repeated spitting, or a fish that misses meals when tankmates approach. Change food size or delivery position early, and make sure each fish can reach food at its preferred depth. Remove leftovers that settle in sheltered areas before the next feeding.

Temperament and Tankmates

This small perchlet typically keeps to a few favored ledges. It may contest the same patch of rock with small gobies, blennies, or other perchlets. Provide separate perches and observe fish that share the bottom.

Choose calm fish that feed in other parts of the aquarium. Shrimp-sized animals near the rockwork can be treated as prey, and fast feeders may take food before it reaches the perch.

Signs of incompatibility include a fish that repeatedly misses meals, stays in one corner, shows damaged fins, or is chased from shelter. Use rockwork to break up sight lines and provide a second feeding location beyond the dominant fish’s range. Keep a divider or alternate space available if the problem persists.

Small ornamental shrimp and tiny crustaceans are vulnerable. Give this fish its own perches if keeping other bottom dwellers.

Reef Compatibility

The Geometric Pygmy Hawkfish is Reef Safe Caution. The fish generally leaves corals alone, but small ornamental shrimp and other bite-sized crustaceans can be eaten.

Plan the display around those prey risks and monitor food reaching other reef inhabitants. Use filtration and regular maintenance to control nutrients from frequent feedings.

Water Parameters

Temperature: 75–78°F
Specific Gravity: 1.024–1.026
pH: 8.1–8.4
Alkalinity: 8–12 dKH

Use a fully cycled system with undetectable ammonia and nitrite. Maintain steady salinity through top-off and match new saltwater to the aquarium during water changes. Check temperature and circulation after maintenance and during warm weather.

Review feeding portions and filter maintenance together. Regular small meals work best when food is distributed where the fish can take it and the system can remove what remains. Changes in breathing, appetite, or how often the fish leaves cover are worth investigating early.

Check dissolved-waste trends over several feeding days, especially after increasing the number of meals. Keep mechanical media clean and inspect low-flow areas where fine food can collect. Maintain a stable day-night schedule and judge changes in activity against the fish’s normal behavior at the same time of day.

Common Considerations

• Adult Housing: Use 30 gallons or more for adult housing. Up to 1.8 inches (4.5 cm, standard length).
• Feeding: Offer one or two small meals daily as a starting point. Small ornamental shrimp and tiny crustaceans are vulnerable. Give this fish its own perches if keeping other bottom dwellers.
• Shelter and Flow: This perchlet spends much of its time perched in crevices. Arrange small ledges and place food where it can make a short strike from shelter.
• Tankmate Monitoring: Confirm that each fish can use its shelter and feed without repeated pursuit.
• Reef Compatibility: Choose tankmates with the risk to small prey animals in mind.
• Acclimation: Provide a secure cover, stable water, and access to suitably sized foods while the fish settles.