One characteristic that makes coral reef fish communities so appealing to aquarists is the diversity. The fish that live in this ecosystem exhibit so many different shapes, colors and lifestyles. To reduce some of the competition between species, the coral reef has defined night and day shifts. At dusk, many species that feed during the day take shelter in the reef, while other species emerge from their daytime sanctuaries to begin making a living in the dark. One group that is a ubiquitous component of the “night shift” are the soldierfish. For the aquarist looking for a fish that is a bit different, a blackbar soldierfish (Myripristis jacobus) may be just what they are looking for. This member of the family Holocentridae (which includes the soldier and squirrelfish) is readily available to home aquarists.
Difficulty: If provided with a cave in which to shelter and a varied diet, the blackbar soldierfish is not difficult to care for. This species loves meaty foods, such as pieces of sea food (e.g., shrimp) or frozen fish food preparations for carnivores. If an individual Myripristis jacobus seems reluctant to eat, try feeding it when only the actinic lights are on.
Physical description: Like some other fish that are active at night, most soldierfish are red (not a common chromatic scheme among coral reef fish) and have large eyes. Their large optical “equipment” enables them to see their food in very limited light. It has been speculated that a full moon is all that is required for soldierfish to see a larger crab larvae. The blackbar soldierfish gets its name from the dark bar present at the rear of the gill cover. The blackbar soldierfish can reach a total length of 8 inches.
Range: Myripristis jacobus is found on both sides of the Atlantic. In the western Atlantic, the blackbar soldierfish occurs from North Carolina all the way south to Brazil. The blackbar soldierfish is commonly imported from the Florida Keys. The blackbar soldierfish is found on patch reefs in lagoon habitats, on reef faces and deeper reef slopes. The blackbar soldierfish has been reported at depths from 15 to over 150 feet. The blackbar soldierfish often hides in caves and crevices during the day, while at night they move out over the reef to feed on larger zooplankton.
Compatibility: The blackbar soldierfish is not a threat to most other fish. The blackbar soldierfish may occasionally quarrel with another fish that enters a preferred hiding place, but it is typically indifferent toward tankmates. That said, a full-grown Myripristis jacobus may eat a smaller fish that it can swallow whole. In nature the blackbar soldierfish often “roosts” in groups during the day. These diurnal groups may occupy a large cave or mill under an overhang. You may be able to recreate this natural social unit in a larger aquarium with a suitably sized reefscape, but more often than not, the blackbar soldierfish will squabble with members of its own kind if space is at a premium. Thus, it is best to keep one or two blackbar soldierfish in the standard home aquarium (e.g., 100 gallons). If you have a large enough aquarium to house a group, add all of the blackbar soldierfish at once. The blackbar soldierfish is sometimes bullied by other crevice and cave dwellers such as squirrelfish (a close relative), larger dottybacks and more hefty damsels.
Aquarium conditions: An adult blackbar soldierfish will feel right at a home in a tank of 100 gallons or more that is complete with rock caves and overhangs from which it can peer out when the aquarium lights are on. Also, a natural cycle of 14 hours of light and 12 hours of dark is also a prerequisite for the blackbar soldierfish and other nocturnal species. Myripristis jacobus can most often be seen during the dawn and dusk period when only the actinic bulbs are on. You can also use a red incandescent bulb over the aquarium or blue moonlight bulbs to observe activity at lower light levels (e.g., simulating the nighttime). A pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 72 to 82 degrees Fahrenheit is suitable for this species. Specific gravity can be dropped down to 1.012 during treatment periods without ill-effect.
Care considerations: Initially, the blackbar soldierfish may be shy and reluctant to spend much time in full view when the lights are on. But in time, as it begins associating its fishkeeper with food and learns that tasty morsels are present during daylight hours, the blackbar soldierfish will become more brazen.
Breeding: The blackbar soldierfish is not likely to breed in the home aquarium.