Black Cap Jawfish

Opistognathus randalli

(0 Reviews)

Black Cap Jawfish

Black Cap Jawfish

Opistognathus randalli

(0 Reviews)

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Black Cap Jawfish Care Facts

Care Level: Easy
Temperament: Peaceful
Diet: Carnivore
Reef Safe: Yes
Minimum Tank Size: 30 gallons
Max Size: 5 inches

The Black Cap Jawfish (Opistognathus randalli) is a unique fish found among the Indo-Pacific. They have a pale/peach body with faint green stripes and a black head. They are peaceful towards other fish, though they should not be kept with very small invertebrates, as they would likely eat them. They reach a maximum size of 5 inches and should be kept in an aquarium of at least 30 gallons with plenty of sand and live rock. Though peaceful towards other tank mates, two males would not get along, so it is recommended to keep them singly or in a bonded pair.  

Black Cap Jawfish (Opistognathus randalli): The Enigmatic Architects of Your Marine Aquarium

Welcome to the world of the Black Cap Jawfish, scientifically known as Opistognathus randalli, where we explore every facet of this intriguing species for your saltwater marine aquarium. This comprehensive guide covers vital information about their natural habitat, reef compatibility, size, lifespan, dietary needs in captivity, compatibility with other aquatic companions, sexual dimorphism, coloration changes from juvenile to adult stages, temperament, specific tank requirements, and essential water conditions. In addition, we provide a list of common names, suggest five compatible tankmates, and explain why acquiring the Black Cap Jawfish from is a wise choice for your marine setup.

Black Cap Jawfish Habitat and Natural Range

The Black Cap Jawfish, Opistognathus randalli, thrives in the warm, tropical waters of the Indo-Pacific region. This species primarily inhabits sandy substrates, lagoons, and rubble areas of coral reefs. They are renowned for their remarkable burrowing behavior, which plays a significant role in their daily life and provides an exciting spectacle for aquarium enthusiasts.

Reef Compatibility of Black Cap Jawfish

Black Cap Jawfishes are considered reef-safe, making them a prized addition to reef aquariums. Their burrowing activities seldom disturb corals and other reef-dwelling invertebrates, allowing for a harmonious coexistence within your aquatic ecosystem.

Size and Lifespan of Black Cap Jawfish

In a well-maintained aquarium, Black Cap Jawfishes can reach a size of up to 4 inches (10 cm). They can live for approximately 5 to 8 years with proper care, providing a lasting and engaging presence in your marine setup.

Diet in Captivity for Black Cap Jawfish

Black Cap Jawfishes have a diverse diet in captivity. To replicate their natural feeding habits, provide a well-rounded diet that includes high-quality marine flakes, pellets, frozen foods, and live offerings. Their diet should combine small crustaceans, mysis shrimp, brine shrimp, and copepods. Maintaining a varied diet ensures their health and vitality.

Compatibility of Black Cap Jawfish with Other Fish and Invertebrates

Black Cap Jawfishes are known for their peaceful temperament, making them an ideal candidate for community aquariums. Here are five compatible tankmates:

  1. Firefish Goby (Nemateleotris spp.): Firefish share a peaceful disposition and come in various colors, adding diversity to your aquarium.
  2. Clownfish (Amphiprioninae): Clownfish are colorful and display interesting behaviors, making them a captivating addition.
  3. Royal Gramma (Gramma loreto): These vibrant fish are known for their striking purple and yellow coloration.
  4. Yellowtail Damsel (Chrysiptera parasema): Yellowtail damsels are small and active and add a splash of bright yellow to your aquarium.
  5. Banded Coral Shrimp (Stenopus hispidus): These fascinating shrimp are functional and visually appealing.

Sexual Dimorphism in Black Cap Jawfish

Black Cap Jawfishes exhibit minimal sexual dimorphism, making it challenging to distinguish between males and females visually. In the aquarium trade, both sexes are typically represented simply as "Black Cap Jawfish."

Juvenile to Adult Coloration Changes in Black Cap Jawfish

Juvenile Black Cap Jawfishes exhibit captivating patterns, with a dark cap-like marking on their head and vibrant body coloration. As they mature into adulthood, their coloration may become even more vivid, and their behavior may become more pronounced.

Temperament of Black Cap Jawfish

Black Cap Jawfishes are renowned for their endearing behavior, which includes constructing burrows in the sandy substrate. These burrows serve as shelter and a vantage point from which they observe their surroundings. Their temperament is peaceful, and they seldom engage in aggressive behavior or territorial disputes. They are jumpers, however. Make sure your aquarium has a full lid.

Tank Requirements for Black Cap Jawfish

Creating an ideal environment is crucial for the well-being of your Black Cap Jawfish. Here are essential tank requirements to consider:

  • Minimum Aquarium Size: A tank with a capacity of at least 30 gallons is recommended to accommodate their burrowing behavior and provide sufficient swimming space.

Detailed Water Conditions for Black Cap Jawfish

Maintaining precise water conditions is crucial for the health and well-being of your Black Cap Jawfish:

  • pH: Maintain a stable pH between 8.1 and 8.4 to support metabolic functions and overall well-being.
  • Salinity: Ensure a stable salinity level within the range of 1.020 to 1.025, replicating the conditions of their native habitat.
  • Water Temperature: Maintain a consistent water temperature between 75°F and 78°F (24°C to 26°C) to promote comfort and reduce stress.
  • Water Flow: Provide gentle to moderate water flow to mimic their natural environment and support water quality.

Other Common Names of Black Cap Jawfish

Apart from being known as the Black Cap Jawfish, Opistognathus randalli may also be referred to by common names such as:

  • Randall's Jawfish
  • Yellowhead Jawfish

Why People Should Buy the Black Cap Jawfish from

When you choose as your trusted source for the Black Cap Jawfish, you gain access to a reputable provider committed to the well-being of marine species. Our specimens undergo meticulous sourcing, quarantine, and acclimation processes to ensure their health and adaptability in your aquarium. Acquiring the Black Cap Jawfish from not only enriches the diversity of your marine environment but also contributes to the sustainability of this captivating species. With its mesmerizing burrowing behavior and beautiful colors, this unique fish elevates your marine aquarium into an engaging and dynamic underwater world.

In summary, with its charismatic burrowing behavior and captivating appearance, the Black Cap Jawfish is a valuable addition to saltwater aquariums. You can enjoy the benefits of an enchanting and tranquil marine environment by meeting their specific care requirements and providing compatible tank mates. Opt for the Black Cap Jawfish from to acquire a healthy specimen that will thrive and captivate your aquarium for years.


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