How To Care For Assessors

Assessor fish are small, peaceful basslets known for their vibrant coloration and unique swimming behavior. These fish often prefer the shadows of rock crevices and caves, making them an excellent choice for aquarists looking to add color and intrigue to their tank. Unlike many other fish, assessors are known for their ability to swim upside down, a behavior that helps them navigate tight spaces in their natural habitat.

These hardy fish are well-suited for reef aquariums, as they are entirely reef-safe and do not pose a threat to corals or invertebrates. With their calm temperament and striking appearance, assessors make a fantastic addition to both beginner and experienced aquarists' tanks.

General Habitat & Tank Requirements:

Tank Size: A minimum of 30 gallons for a single Assessor, but larger aquariums can provide more territory.
Aquascape: Provide ample rockwork with caves and overhangs, as they prefer shaded areas.
Substrate: A sandy substrate is ideal to mimic their natural habitat, but this fish has no specific substrate requirements.

Water Conditions:

Temperature: 75°F to 80°F (23°C to 27°C).
pH: 7.7 to 8.5.
Specific Gravity (Salinity): 1.020 to 1.026.
Water Quality: Maintain ammonia and nitrite levels at 0 ppm, and nitrates below 20 ppm.
Filtration: Employ high-quality filtration, such as a protein skimmer, to ensure optimal water quality.

Diet and Feeding

Assessors are carnivorous and thrive on a diet rich in meaty foods. In the wild, they feed on small crustaceans and zooplankton. In captivity, they readily accept:

Frozen or live foods such as mysis shrimp, brine shrimp, and copepods.
High-quality pellet or flake foods designed for small carnivorous fish.
Frequent, small feedings throughout the day for optimal health.

Behavior and Compatibility

Assessors are mostly peaceful and can coexist with a variety of marine species. They tend to be shy initially but become more confident over time. Their unique swimming behavior and preference for dimly lit areas make them a fascinating species to observe.

Some Compatible Tank Mates

Fish: Clownfish, Wrasses, Blennies, Gobies, Cardinals, and other peaceful community fish.
Invertebrates: Safe with Cleaner Shrimp, Hermit Crabs, Snails, Urchins, and other common invertebrates.
Coral: Reef-safe. They will not bother corals.

Behavioral Notes

Swimming Style: Often seen swimming upside down under ledges or within caves.
Territoriality: Generally peaceful but may be territorial towards other basslets unless housed in a large aquarium.
Hiding Nature: They prefer shaded or dimly lit areas and may take time to become comfortable in open spaces.

Health and Maintenance

Perform regular water changes of 10-25% every two to four weeks to maintain water quality. Regularly test water parameters and observe for signs of stress or illness, such as loss of color, appetite changes, or erratic swimming.

Common Health Issues

Assessors can be susceptible to common health issues in an aquarium environment such as:

Marine Ich: Identified by white spots on the body and rapid breathing.
Marine Velvet: Similar appearance to Ich but more severe, causing a dusty, velvet-like appearance on the skin.
Bacterial Infections: Open wounds from aggression or handling can become infected, leading to redness, swelling, or ulcerations.

Maintaining excellent water quality, providing the right nutrition, and giving the fish a stress-free environment can prevent most health issues.