Boenacki (Blueline) Grouper

The Boenak Blueline Grouper, Cephalopholis boenak, is a compact but striking predatory marine fish with rich brown to reddish-brown coloration, subtle darker vertical bars, and contrasting pale margins along portions of the fins. Depending on mood, lighting, and maturity, its coloration can shift considerably, giving this grouper a dynamic appearance within the aquarium.

Native to the Indo-West Pacific from East Africa through Southeast Asia and into the western Pacific, this species is primarily associated with protected coastal reefs, including silty coral and rocky reef habitats. It tends to remain close to structure, using caves and overhangs as ambush points while watching for small fish and crustaceans.

Reaching approximately 12 inches as an adult, the Blueline Grouper is considerably more manageable than many of the giant grouper species encountered in the marine aquarium trade. Its compact adult size, bold personality, and predatory behavior make it an appealing centerpiece for a large fish-only aquarium or a carefully planned reef aquarium where smaller fish and ornamental crustaceans are not present.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 125 gallons
Temperament: Predatory
Diet: Carnivore
Reef Safe: With Caution
Region: Indo-West Pacific
Scientific Name: Cephalopholis boenak

Tank Requirements

The Blueline Grouper should be provided with substantial rockwork containing caves, ledges, and shaded retreats. Although it is not an exceptionally active open-water swimmer, an adult still requires adequate room to move comfortably between territories and should not be confined by overly dense aquascaping.

Create one or more secure caves large enough to accommodate the adult fish while maintaining open areas toward the front and center of the aquarium. Rock structures should be firmly positioned, particularly in systems containing larger predatory tankmates.

Substrate choice is flexible, and either sand or a bare-bottom setup can work well. Efficient mechanical and biological filtration is important because a carnivorous grouper produces considerably more waste than many similarly sized community reef fish.

Moderate water movement, excellent oxygenation, and stable water quality are recommended. A secure aquarium cover is also beneficial, especially during acclimation or territorial encounters.

Diet and Feeding

The Blueline Grouper is a carnivore that naturally feeds primarily on small fish and crustaceans. Captive specimens generally adapt well to a varied diet of high-quality marine foods once established.

Offer mysis shrimp and krill to smaller specimens, along with appropriately sized pieces of shrimp, squid, clam, mussel, scallop, and marine fish flesh as the grouper grows. Quality frozen carnivore blends can also provide useful nutritional variety.

A varied diet is preferable to feeding one type of seafood exclusively. Juveniles can be offered smaller meals daily, while established adults may be fed several substantial meals per week according to body condition.

Avoid routine use of live feeder fish. They are unnecessary for maintaining this species and can introduce nutritional and disease concerns.

Temperament and Tankmates

The Blueline Grouper is a predatory and somewhat territorial fish that spends much of its time around caves and reef structure. It may appear relatively reserved when first introduced but typically becomes bolder once established and accustomed to feeding.

Any fish small enough to fit into its mouth should be considered potential prey. Suitable tankmates include appropriately sized tangs, larger angelfish, robust wrasses, triggerfish, rabbitfish, and other semi-aggressive marine fish that cannot be swallowed.

Small clownfish, gobies, cardinalfish, dartfish, chromis, and other compact community species may eventually be eaten, even if they initially coexist without incident.

It is generally best to keep a single Blueline Grouper unless the aquarium is exceptionally large and specifically designed to accommodate multiple territorial predators.

Reef Compatibility

The Blueline Grouper is reef safe with caution. It does not typically consume healthy coral tissue and can be maintained in a coral aquarium from that standpoint.

The primary concern is predation. Ornamental shrimp, small crabs, and other suitably sized crustaceans may be eaten, and small reef fish are also at significant risk. Snails and larger established invertebrates are generally less likely to attract attention, although individual behavior can vary.

This species is therefore best suited to a predator-style reef aquarium containing corals and appropriately sized fish rather than a traditional community reef stocked with small fish and ornamental shrimp.

Water Parameters

Temperature: 75–80°F
Specific Gravity: 1.024–1.026
pH: 8.1–8.4
Alkalinity: 8–12 dKH

Stable salinity, strong biological filtration, good oxygenation, and consistently clean water are more important than attempting to maintain an exact value within these ranges.

Common Considerations

• Predatory feeding behavior: Small fish and ornamental crustaceans should be considered potential prey.

• Adult size: Although smaller than many groupers, adults can still reach approximately 12 inches and require substantial permanent housing.

• Caves are important: Provide secure rockwork and shaded retreats where the fish can establish a territory.

• Heavy feeding produces waste: Strong filtration and disciplined feeding help maintain long-term water quality.

• Choose tankmates by adult size: Fish that appear safe with a juvenile grouper may become vulnerable as the grouper matures.