Yellow Assessors are found in shaded caves, overhangs and ledges where they often hover upside down or at unusual angles beneath the rockwork. Its natural range is Great Barrier Reef, Coral Sea and western Pacific shaded reef caves. These fish are closely associated with rock, coral bases, ledges or cave openings, so they feel safest in aquariums with layered aquascaping and multiple retreat points. Open, bare tanks can make them nervous or overly defensive, while a structured reef gives them clear boundaries and reduces stress.

Yellow Assessor has the body shape and behaviour expected from its group, with quick movement, alert eyes and a preference for staying near shelter. Colour and markings are species-specific, but healthy specimens should show clear fins, strong body condition and confident feeding. The adult size is generally 5–6 cm, making this species suitable for carefully planned marine aquariums where space and tank mates are considered.

Temperament is best described as Peaceful and shy to moderately confident. Grammas and assessors are usually more peaceful cave dwellers, while many dottybacks can be bold and territorial despite their small size. Suitable tank mates include clownfish, cardinalfish, gobies, blennies, peaceful wrasse, chromis and appropriately sized tangs in larger systems. Avoid adding this fish to tanks dominated by large predators or very aggressive damsels, and avoid mixing similar dottybacks unless the aquarium is large with plenty of broken rockwork.

This species should be fed as a Small carnivore; copepods, mysis, enriched brine shrimp, finely chopped seafood and small pellets. Offer small portions once or twice daily and vary the diet to maintain colour, body weight and immune strength. Frozen mysis shrimp is an excellent staple, while enriched brine shrimp can help new arrivals begin feeding. Small sinking pellets or finely chopped seafood are useful once the fish is settled. Because these fish often feed close to rockwork, ensure food reaches their territory rather than being taken only by faster open-water swimmers.

Provide a minimum aquarium size of 75 L, with 120 L or larger recommended for long-term comfort or community setups. Maintain temperature at 24–27°C, pH 8.1–8.4 and salinity 1.024–1.026. Moderate water flow is ideal, with calmer pockets near caves. Lighting can match the reef system, but shaded retreats are important. Use strong biological filtration, a quality protein skimmer and regular water changes of 10–20% as needed to keep nitrate and phosphate stable. Aquascaping should include caves, overhangs and visual barriers. This fish does not school and is usually kept singly unless a known compatible pair is supplied.

Captive breeding has been achieved by specialist breeders. In display tanks, pairs may show courtship, but larval rearing needs dedicated food cultures. In many cave-dwelling marine fish, spawning behaviour involves cleaning a protected surface or nest site and defending the area. Larval rearing is rarely simple because fry require very small live foods, stable water and separate rearing systems. Most hobbyists should focus on providing stable care and watching for natural courtship behaviour rather than expecting easy breeding in a display tank.

Suitable tank mates include peaceful clownfish, cardinalfish, gobies, blennies, peaceful wrasse, chromis, assessors, grammas, small tangs in larger systems and robust reef-safe invertebrates. Choose tank mates that are not small enough to be bullied and not aggressive enough to trap the fish away from food.

Avoid keeping with large predatory fish, aggressive triggers, lionfish, groupers, highly aggressive damsels, multiple similar dottybacks in small aquariums, delicate timid fish that cannot compete for food, and very small ornamental shrimp if the species is known to be predatory.

See how Yellow Assessor | Assessor flavissimus gets along with the rest of your tank. Our Aquarium Compatibility Checker scores tank size, aggression, diet and water type against everything else you're keeping.

Open the Compatibility Checker for Yellow Assessor | Assessor flavissimus →

Is your tank ready?

A few quick checks before you buy save most of the common losses.

Tank size for the adult, not the juvenile

Check the species page for max size and minimum tank size, and size your tank for what this animal will grow into — not what it looks like today.

Cycle first

Your tank needs an established nitrogen cycle before livestock goes in. Adding fish to an uncycled tank is one of the most common causes of early losses.

Match the conditions

Check temperature and pH on the species page against what your tank currently runs, and make sure you've got the right gear — a heater for tropical species, adequate filtration turnover, lighting and CO2 for planted tanks, or the right salinity setup for marine.

Start conservative

New to the hobby? Start with a small number of hardy species and add slowly — overstocking a new tank is one of the fastest ways to crash your water quality.

Ready to place your first order? See our Buying Livestock Online — Start Here guide for the full walkthrough of packing, delivery, arrival day and acclimation.

Where we ship

We are based in Brisbane and ship live fish and corals to most of Australia. Some states have import rules that may affect what we can send and the cost.

• Western Australia: Import requirements and fees may apply. Read first.
• Tasmania: Import requirements and fees may apply. Read first.
• Northern Territory: May require a permit and be subject to quarantine.
• Regional and remote areas: Carrier options can be limited, which may affect service and transit time.

If you are unsure we can reach your location, please contact us before ordering.

A note on timing: All transit times are estimates and can vary with your location, the weather, and carrier schedules. Regional and remote areas may take longer. To give your livestock the safest trip, please order early in the week.

Live Fish

• Oxygen-filled bags — each fish is bagged in clean water from its own system with a generous charge of pure oxygen, giving many hours of safe transit time.
• Double or triple bagging — spiny or sharp-finned species (catfish, plecos, marine oddballs) are multi-bagged with liners so a spine can't cause a leak.
• Dark, calm transit — bags are packed upright in the dark, which keeps fish calm and lowers their oxygen use during the trip.

Live Corals & Inverts

• Individually bagged or cupped — each coral travels in its own bag or rigid cup of system water, sized so the piece can't knock against the sides.
• Frags secured — frag plugs are held so they can't tumble or land face-down against the polyps.
• Inverts packed to species — shrimp, snails, starfish and anemones each get the packing method that suits them, not a one-size-fits-all bag.

Live Plants & Tissue Cultures

• Moist, not swimming — plants travel wrapped in damp paper inside sealed bags, which prevents both drying out and rot in transit.
• Tissue culture cups sealed — cultures stay in their sterile cups, cushioned so lids can't pop.

The Box

• Insulated foam boxes — all livestock ships in polystyrene-lined cartons to hold temperature steady.
• Heat or cool packs by season — we add heat packs in winter and cool packs in summer heat waves, based on the forecast for your delivery route.
• Void fill and bracing — bags are braced so nothing shifts, even if the box travels on its side.

When Your Box Arrives

Open the box promptly, check everyone in, and follow our Acclimation Guide before releasing anything into your tank. If something has gone wrong in transit, take photos of the unopened bags straight away and see our Live Fish Arrival Guarantee for what to do next.

Questions about packing or shipping to your area? Email us at sales@nicksaquariumoceanariumterrarium.com.au — we're always happy to talk through it before you order.

Dead on Arrival (DOA) Cover

DOA cover applies only to livestock shipped by air freight. It gives you peace of mind that eligible animals are covered if they arrive deceased. Full terms are in our Live Fish Arrive Guarantee.

How to make a claim

• Take clear photos or video of the deceased livestock in the sealed, unopened inner bag.
• If double bagged, you may remove the outer bag, but the inner bag must stay sealed.
• Take individual photos or video of each animal once unbagged, where applicable.
• Send your claim by email or text message within 4 hours of receiving your order. Claims by Facebook Messenger or phone cannot be accepted, and claims made after 4 hours may be declined.
• Please include: your name, order number, approximate time received, number of bags affected, and quantity of livestock affected.

If your claim is approved

We will offer store credit or a replacement of the same item, subject to availability. Replacement shipping is covered only if more than 50 percent of your order arrives DOA. Shipping charges and fees are non-refundable.

To keep your cover valid

Be present at the airport or at home to receive your order, and collect it promptly. Livestock left unattended, returned to a depot, or delayed in collection may void cover. We can only ship to a valid residential or business address, not PO boxes or third-party addresses.

Why quarantine

Quarantining new arrivals before they go into your main tank protects the fish you already have from disease, and gives new stock time to settle and start feeding under close observation.

Freshwater Fish

• Duration: 2 to 4 weeks in a bare-bottom tank with a cycled sponge filter.
• Watch for: white spots, flicking or scratching, laboured breathing, clamped fins, and loss of appetite, checked twice daily.
• Medication: only if a problem appears — quarantine is for observation, not routine treatment.

Marine Fish

• Duration: around 4 weeks minimum.
• Options: observation only, a copper treatment held at 2.0 to 2.5 ppm for at least 30 days, or the Tank Transfer Method (four transfers over about 12 days).
• Flukes and worms: treated with praziquantel, with a repeat dose about a week after the first.

Full details: see our Fish Quarantine Guide, and our Freshwater Fish Quarantining at Home and Marine Fish Quarantining at Home guides, for tank setup, dosing, and day-by-day steps.

Before you start

Test your aquarium water, gather a clean bucket and net, and dim the room lights. Never pour transport bag water into your aquarium — always net your livestock out and discard the bag water, since acclimating too quickly after CO2 build-up in the bag can make trapped ammonia rapidly more toxic.

Freshwater Fish

Float the sealed bag for about 15 minutes to match temperature, then open it into a bucket and add roughly a cup of aquarium water every 5 minutes for about 45 minutes. Net the fish into the tank, keep the lights off for the rest of the day, and hold off feeding until the next day.

Marine Fish

Use the same cup method as freshwater fish, but keep the lights off or dimmed for at least 12 hours after introduction, and hold off feeding until the next day. We recommend quarantining marine fish before adding them to your display.

Corals, Clams & Invertebrates

• Drip acclimation is recommended: 1 to 2 drops per second until the bucket volume has at least doubled, around 45 minutes for fish-safe inverts and 60 to 90 minutes for corals and clams. Echinoderms such as starfish, urchins and sea cucumbers need the slowest acclimation of all.
• Handle corals and clams by their base, skeleton or frag plug only — never the soft tissue, polyps or mantle.
• Light acclimation: place new corals low in the tank away from strong light and flow for the first few days, then raise them gradually over 1 to 2 weeks.

Full details: see our Acclimation Guide for the complete drip and cup methods and coral dipping.