Assesor Yellow (Assessor Flavissimus)

Yellow Assessor (Assessor flavissimus)

The Yellow Assessor is a peaceful and highly desirable "hidden gem" of the marine aquarium world. While it shares the bright coloration of more common fish like the Yellow Coris Wrasse or Herald’s Angelfish, it is distinguished by its unique swimming behavior and cryptic nature. It is famous for its habit of swimming upside down along cave ceilings and overhangs, making it a fascinating addition to a mature reef tank.

Key Information

• Common Name: Yellow Assessor, Golden Assessor

• Scientific Name: Assessor flavissimus

• Origin: Western Central Pacific (Great Barrier Reef)

• Max Size: 5–7 cm

• Lifespan: 5–8 years

• Temperament: Peaceful and somewhat shy

• Diet: Carnivore – requires small meaty foods like cyclops, mysis, and enriched brine shrimp

• Care Level: Easy to Moderate

Water Parameters

• Temperature: 22–26°C

• pH: 8.1–8.4

• Specific Gravity: 1.020–1.025

• Minimum Tank Size: 75L (20 Gallons)

Behaviour & Tank Compatibility

The Yellow Assessor is the perfect resident for a quiet reef tank. Unlike the aggressive Arabian Dottyback, this fish is a "good neighbor" that will not harass other inhabitants.

• Upside-Down Swimming: Do not be alarmed—this is their natural behavior! They prefer to hover near vertical or inverted surfaces.

• Social Structure: They can be kept singly or in small groups in larger aquariums, provided there is enough rockwork.

• Tank Mates: Best kept with other peaceful species like Firefish, Blennies, and Mandarins. Avoid large, boisterous, or aggressive fish that might intimidate them into permanent hiding.

• Reef Safe: 100% Reef Safe. They do not nip at corals, clams, or even small ornamental shrimp.

Ideal Tank Setup

• Rockwork: This is the most critical element. They require caves, overhangs, and deep crevices. Without these, the fish will be highly stressed and lose its vibrant color.

• Lighting: They naturally inhabit deeper or shaded areas. While they can adapt to bright reef lights, they appreciate plenty of shaded zones to retreat to.

• Lid: Like many small, elongated fish, they are expert jumpers. A tight-fitting lid or mesh cover is mandatory.

Why Choose the Yellow Assessor?

The Yellow Assessor is for the hobbyist who appreciates unusual behavior and a calm tank dynamic. It provides a splash of solid, glowing yellow that stays small enough for nano reefs. While they can be more expensive and harder to find than other yellow fish, their hardiness and peaceful nature make them a superior choice for a high-quality reef display.