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Yellow Assessor
Basslet

Yellow Assessor

Assessor flavissimus

A solid butter-yellow fish from the northern Great Barrier Reef that lives under ledges and inside caves, and is regularly seen swimming upside down along the roof of an overhang. It is a plankton feeder, not a hunter, so it leaves shrimp, snails and corals alone and works well in a small reef where a dottyback would not. Temperament is mild for a cave-holder — it may push at a fish that wants the same overhang, but it does not patrol the tank. Keep one per tank unless there are several separate caves, and cover the tank, as assessors do jump.

Temperament
Peaceful
Max size
2.8"
Min tank
30 gal
Reef-safe
Reef safe
Diet
Planktivore
Zone
Caves, Rockwork, Mid-water
Keep just one per tank — two will fight.
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Tankmates

How Yellow Assessor gets on with the rest of the reef, checked pair by pair by the same engine as the live pre-flight.

Best kept apart

A real clash — aggression, predation or a same-genus fight.

Maroon ClownfishMaroon Clownfish (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Purple TangPurple Tang (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Coral HawkfishSmall, peaceful cave-dwellers are documented targets for the Coral Hawkfish, and the Yellow Assessor is one of the most easily bullied fish in the hobby.Antennata LionfishAntennata Lionfish has a big enough mouth to eat the much smaller Yellow Assessor.Picasso TriggerfishPicasso Triggerfish (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Fourline WrasseThe Fourline Wrasse is documented as extremely aggressive toward peaceful and docile species, and the Yellow Assessor is a shy fish that simply withdraws and stops feeding.Neon DottybackThe Yellow Assessor is a shy cave-dweller frequently targeted by bullies, and the Neon Dottyback is documented as untrustworthy with anything less dominant than itself. They also want the same overhangs.Royal DottybackYellow Assessors are described as frequently the target of bully tankmates and turn withdrawn when housed with aggressive fish. The Royal Dottyback is exactly that bully, and it wants the same caves.Domino DamselDomino Damsel (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Blue AssessorYellow Assessor and Blue Assessor are the same genus (Assessor) and will fight — keep only one.Marine BettaMarine Betta has a big enough mouth to eat the much smaller Yellow Assessor.Dragon WrasseDragon Wrasse has a big enough mouth to eat the much smaller Yellow Assessor.Volitans LionfishVolitans Lionfish has a big enough mouth to eat the much smaller Yellow Assessor.Zebra Dwarf LionfishZebra Dwarf Lionfish has a big enough mouth to eat the much smaller Yellow Assessor.Snowflake MoraySnowflake Moray has a big enough mouth to eat the much smaller Yellow Assessor.Zebra MorayZebra Moray has a big enough mouth to eat the much smaller Yellow Assessor.Chainlink MorayChainlink Moray has a big enough mouth to eat the much smaller Yellow Assessor.Golden Dwarf MorayGolden Dwarf Moray has a big enough mouth to eat the much smaller Yellow Assessor.Rectangle TriggerfishRectangle Triggerfish (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Clown TriggerfishClown Triggerfish (aggressive) is much larger than the peaceful Yellow Assessor and may harass it.

Keep an eye on these

Usually fine, but worth watching in a smaller tank.

Sailfin TangSailfin Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Powder Blue TangPowder Blue Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Royal GrammaBoth are small cave-dwellers that hover upside-down under a ledge and defend that spot. The gramma is territorial toward fish that behave like it, so give them separate caves or a tank over about 75 gallons.Red Coris WrasseRed Coris Wrasse (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Convict TangConvict Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Emperor AngelfishEmperor Angelfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Regal AngelfishRegal Angelfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Achilles TangAchilles Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Naso TangNaso Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Scopas TangScopas Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Queen AngelfishQueen Angelfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Blueface AngelfishBlueface Angelfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Chevron TangChevron Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Mimic TangMimic Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Powder Brown TangPowder Brown Tang (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Blue-Throat TriggerfishBlue-Throat Triggerfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Crosshatch TriggerfishCrosshatch Triggerfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Niger TriggerfishNiger Triggerfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Threadfin ButterflyfishThreadfin Butterflyfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.Majestic AngelfishMajestic Angelfish (semi-aggressive) is much larger than the peaceful Yellow Assessor and may harass it.