Elegant Firefish (Nemateleotris decora)

A hovering dartfish that needs a lid and calm company

The Elegant Firefish (Nemateleotris decora), also called the purple firefish, is a slender marine dartfish from the tropical Indo-West Pacific. FishBase records it from Mauritius east to Samoa, north to the Ryukyu Islands and south to New Caledonia, usually at 25–70 m, and gives a maximum length of 9.0 cm total length. It spends its day hovering just above the rock, picking tiny food from the water, and dives into a hole the moment it is alarmed.

It suits a keeper with a mature marine aquarium, plenty of rock crevices, a secure lid and peaceful fish that leave it room to feed. It is a poor fit for a busy community of boisterous fish, an open-topped aquarium or a system that already holds another dartfish species.

Why keepers choose it, and who should look elsewhere

OATA names the purple firefish as one of the two most popular dartfish in the trade, alongside the red firefish, and Wikipedia notes that it is popular in reef aquariums and that firefish are commonly kept in nano reefs. The appeal is its colour and its behaviour: a fish that hangs in the current near its hole, picking food from the water, then vanishes in an instant. That same behaviour is the reason to think twice if you want a fish that owns the front glass of a busy community aquarium. Around boisterous fish, a firefish spends its time hidden and can miss its food, so it rewards a calm, well-planned aquarium far more than a lively one.

Key numbers before you buy

What one purchase includes

One fish, chosen by species rather than sex

Each purchase supplies one live Elegant Firefish. Sex is guaranteed only when the selected option explicitly states male or female. This Elegant firefish listing has no sex-guaranteed option. OATA notes that sexing dartfish is difficult unless they are in breeding condition, so two firefish bought together should be planned as two individuals rather than a known male and female. The section on pairs and groups in the compatibility tab explains what that means for stocking.

Names you may meet

Elegant firefish and purple firefish are both names for Nemateleotris decora, which Wikipedia credits to Randall and Allen, 1973. FishBase places the species in the family Microdesmidae, while OATA's care sheet groups the firefish with the dartfish in the family Ptereleotridae; both refer to the same fish. Some researchers treat the western Indian Ocean populations as a separate species, Nemateleotris exquisita, though that split still needs more taxonomic work. FishBase lists the species as Least Concern on the IUCN Red List.

Do not confuse it with the fire goby, a trade name for the red firefish, Nemateleotris magnifica. That is a different dartfish species, and OATA advises that different dartfish species should not be mixed, so treat the two as alternatives rather than companions.

Colour and the gallery

Wikipedia describes a purple head and a whitish or yellowish body that darkens towards the tail, with fins carrying long bands of purple, red, black and orange. The photographs show that pattern: a violet snout, a pale body shading to purple, a tall red-edged first dorsal fin and red-trimmed rear fins. Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals. Several gallery scenes show plants and driftwood; the fish itself needs a marine aquarium built around rockwork, as the care tab sets out. Browse the marine fish we keep when planning the rest of the aquarium, checking each candidate against the compatibility tab.

How it lives on the reef

FishBase describes adults on deep outer coastal reefs and outer reef drop-offs swept by moderate to strong currents. They are found over hard, open bottoms at the bases of reefs and over patches of sand and rubble, across a depth range of 25–100 m and usually 25–70 m. The species is often seen in pairs and is monogamous. It feeds on zooplankton, especially copepods and crustacean larvae, and darts into a hole when alarmed.

OATA's jawfish and dartfish care sheet fills in the behaviour an aquarist sees: dartfish live in caves or crevices and spend their time in the water column waiting for planktonic food to drift by. When frightened, they dart into their burrow, which is where the group gets its name.

What that means in your aquarium

• Shelter first. A fish whose defence is a quick dive into a hole needs that hole within easy reach wherever it hovers. Without it, the fish has nowhere to go when startled.
• Food in the water column. It picks small food from open water rather than grazing rock or sifting sand, so feeding is about getting small items past it before faster fish take them.
• Current, but not chaos. Wild fish live where currents carry plankton past. OATA asks for moderate flow in the aquarium: enough surface movement and circulation to keep detritus from settling and to let the fish feed naturally.
• A deep-water animal. Its wild range starts well below the shallows. Treat those depths and FishBase's 23–27°C wild temperature record as natural history; the aquarium targets come from the water section below.

Build the aquarium around a bolt-hole

Size and stability

OATA recommends an aquarium of at least 60 litres for an individual dartfish, and says it will need to be larger if you keep more than one or mix dartfish with other species. Bigger is better within reason: a larger volume keeps temperature and water quality more stable.

Filtration

A filter is essential whatever the size. For a marine set-up, OATA lists live rock with sufficient water flow, an internal or external filter, or a sump. A protein skimmer is a useful addition because it removes dissolved organic waste before it breaks down into more harmful substances.

Rockwork and sand

Live or artificial rockwork is essential for dartfish. Build it to give crevices, overhangs and outcrops so the firefish can find cover whenever it needs to, and place several bolt-holes near the open water where it will hover. OATA adds that dartfish may appreciate a slightly thicker sand bed than usual, about 4 cm, so they can make a home under rocks if they choose.

The lid is not optional

OATA calls an aquarium lid or cover essential because dartfish will jump, especially if startled, and Wikipedia describes firefish as prolific leapers. Close every gap around pipework, cables and feeding hatches before the fish arrives, and keep the cover in place during maintenance whenever you can.

A worked layout

In a 60 litre aquarium, build one main rock structure with two or three bolt-holes opening towards the open water where the firefish will hover. Keep about 4 cm of sand along the rock edges so it can settle under the rock if it chooses. Set the flow so the surface moves well and food drifts along the face of the rock rather than straight into the sand, and leave a clear strip of open water in front of the structure. In a larger aquarium, repeat the pattern with more bolt-holes spread along the rockwork, so the fish always has cover within a short dash of wherever it feeds.

Before you order: equipment and readiness

OATA's care sheet ends with a checklist worth working through before a firefish is ordered. Make sure you have the right equipment and position for the aquarium, have researched every species you are considering and confirmed they are all compatible, know how to transport and release the fish, understand the daily, weekly and monthly maintenance involved, and are prepared to look after the fish properly for the rest of its life.

Shopping list

OATA lists an ultraviolet steriliser as optional but recommended, and reef test kits for calcium, alkalinity, magnesium and phosphate as necessary only if you keep corals.

Where the aquarium stands

Keep it away from draughts, heat sources and direct sunlight to limit temperature swings, and away from loud noise, vibration and sudden movement. Overhead lighting gives the fish a proper day-night cycle; it does not need to be bright for dartfish alone, though corals may need more.

Ready to receive fish

OATA's final checks are simple: the aquarium is a suitable size for the fish when fully grown, the water values match the guidance in the next section, and the aquarium is cycled and ready.

Water values and weekly tests

Keep the Elegant Firefish at 24–26°C, pH 7.9–8.3 and a salinity of 1.020–1.025, with ammonia and nitrite at zero. These are OATA's broad guidance figures for dartfish and jawfish as a group rather than a species-specific optimum, and OATA describes dartfish as usually undemanding of water chemistry. The temperature range sits inside the 23–27°C that FishBase records for the species' wild environment.

In a reef aquarium

OATA notes that if you keep dartfish in a reef aquarium, some of these values will need to change to suit more sensitive species. Run a reef to the needs of its most sensitive corals and invertebrates, and keep testing so every change is gradual rather than sudden.

Why zero ammonia and nitrite matters so much

The RSPCA's aquarium guidance explains the chain: fish release ammonia, which is toxic; a working biological filter grows bacteria that turn it into nitrite, also toxic, and then into nitrate, which is safer. OATA warns that dartfish can be stressed by even the smallest amounts of ammonia and nitrite, which may then cause them to develop various diseases.

The weekly test

Test ammonia, nitrite, nitrate, pH and carbonate hardness every week, and more closely during the first weeks of a new set-up and after adding fish. Check salinity regularly too, and replace water lost to evaporation with reverse osmosis (RO) water rather than salt water, because the salt stays behind when water evaporates.

Reading the results

A maintenance routine that protects the filter

OATA strongly recommends a partial water change of 25% at least once every week, using a siphon to lift solid waste from the substrate as you go. The table turns that into real volumes.

Cleaning the filter without losing its bacteria

1. Check filters regularly and clean them before they block.
2. Do not run filter media under the tap: chlorine or chloramine may kill the bacteria established in the media.
3. Rinse the media lightly in the aquarium water you have just removed during the water change, which limits how many bacteria are lost.
4. Clean the protein skimmer regularly so it keeps working well.

Adding fish without overwhelming the filter

OATA explains that the bacteria in a matured filter must increase every time fish are added and feeding increases. Stocking too many fish, or stocking too quickly, can cause new tank syndrome: there are not enough nitrifying bacteria to cope with the extra waste, ammonia and nitrite rise, and fish may become ill or die. Before the firefish goes in, confirm ammonia and nitrite read zero, and then add further fish slowly.

A worked week

In a 100 litre aquarium, a sensible week might look like this: daily checks that the firefish is hovering and feeding, one 25 litre water change with the siphon run over the sand, a weekly test of ammonia, nitrite, nitrate, pH and carbonate hardness, salinity checks with RO top-ups in between, and filter or skimmer cleaning when needed, using the water you removed. If a test shows ammonia or nitrite above zero, deal with that before feeding more or adding fish.

Feeding a small zooplankton picker

In the wild the Elegant Firefish feeds on zooplankton, especially copepods and crustacean larvae. OATA's dartfish advice translates that into aquarium food: dartfish will usually take prepared pellets or flake, and they also appreciate smaller frozen items such as frozen copepods, enriched brine shrimp and finely chopped mysis or krill.

How much and how often

Feed only what the fish can eat within a few minutes, twice a day. Overfeeding leads to a build-up of uneaten food, which breaks down and releases toxic waste into the water, so err on the side of less and watch the leftovers.

Making sure it actually eats

OATA warns that dartfish are easily intimidated by boisterous tank mates and should be kept with fish that allow them to come out to feed. A firefish that is bullied at feeding time retreats to its hole while faster fish take the food. Practical ways to help:

• Choose tank mates that feed calmly; the compatibility tab covers this in detail.
• Release small frozen items into the current near its usual hovering spot, so they drift past within reach of its bolt-hole.
• Offer food in small portions rather than one large dose, and watch who eats each portion.
• Include small frozen foods such as copepods alongside pellets or flake, reflecting the zooplankton it eats in the wild.

Signs the routine is right

A well-fed firefish hovers in the open, takes food as it drifts past and keeps a steady body condition. OATA lists reduced intake, lack of interest in food and changes in body weight among the signs to watch, so note appetite at every feed during the first weeks.

Arrival day and the first week

Your firefish is hand-packed by our team, bagged in pure oxygen in an insulated poly box, with a heat pack when the weather calls for it, and travels with a licensed live-animal courier. We email the tracking number and your confirmed delivery date, and someone needs to be home to receive the parcel because live fish cannot be left unattended. Our delivery and Live Arrival Guarantee page has the full terms.

On the day

1. Receive the parcel at the delivery address.
2. Begin a continuous unboxing video with the parcel still sealed and the outer box in view, and keep filming in one take until the fish can be seen inside its sealed bag.
3. Open and inspect the parcel the same day it arrives.
4. Float the bag in the aquarium for 20–30 minutes before releasing the fish, and acclimatise it slowly.
5. Never pour the bag water into your aquarium.
6. If anything has gone wrong, contact us the same day, WhatsApp is fastest, with your order number and the unboxing video, and we will arrange a replacement or refund.

Make sure the lid is back on before you walk away: a newly released firefish is at its most easily startled. OATA explains why bag water stays out, especially in a reef: some retailers run copper in their systems, and copper is toxic to invertebrates.

Ready before the courier arrives

• Ammonia and nitrite tested at zero, and salinity and temperature inside the guidance.
• Lid fitted and every gap around pipework and cables closed.
• Bolt-holes open in the rockwork near the open water.
• A quarantine aquarium running, if you use one.

OATA's advice for the first week

OATA suggests switching off the aquarium lights and taking the bag out of its outer wrappings carefully, avoiding exposure to bright light, because fish are easily stressed by bright lights, extreme temperatures, noise and movement. Monitor the new fish carefully for the first week, paying particular attention to water quality. If you can, OATA recommends quarantining new livestock in a separate aquarium for at least a week before it enters the main display, which reduces the risk of spreading disease.

Expect the firefish to spend time in its bolt-hole at first. Look for it hovering near cover and taking food, rather than expecting it in open water on day one.

Health checks worth making every day

OATA describes a healthy fish as having clear, bright eyes, undamaged fins, intact scales, no ulcers or bumps, normal swimming and steady breathing. Signs of disease can include clamped fins, flicking against rock or décor and shimmying. Because disease can be carried by fish that show no signs, good water quality and careful observation are your main protection.

All fish vary slightly in behaviour and appearance, so learn what normal looks like for your firefish in its first fortnight. Its usual hovering height, favourite bolt-hole and feeding response make the best baseline. If you are concerned, test the water first, then contact us with your readings and a description of what you have seen.

Pairs and breeding: what to expect

FishBase notes that the Elegant Firefish is often found in pairs and is monogamous, and Wikipedia records that this and other firefish species are occasionally spawned in captivity. OATA sets realistic expectations for dartfish in general:

• There are some successful reports of dartfish breeding, but it is highly unlikely in a home aquarium.
• The female deposits eggs in a cave, and the male tends them.
• In the wild, the hatched larvae drift in ocean currents while they develop.
• In a home aquarium, the larvae are too delicate to survive: they are likely to be drawn into filters and pumps or eaten by other fish.
• Raising them needs specific live feeds and a specialist set-up.

Buy an Elegant Firefish for its looks and behaviour rather than as a breeding project. If a pair does form and you see eggs tended in a cave, treat it as a bonus and keep water quality stable; do not rearrange the rockwork around them.

Choosing calm companions

Keep the Elegant Firefish with calm fish that let it come out to feed, and do not mix it with other dartfish species. Those two rules, both from OATA, decide most stocking plans.

Good matches

OATA names cardinalfish and small gobies as examples of fish that allow dartfish to come out and feed. Wikipedia describes the firefish itself as relatively docile, noting that it will not attack tank mates in a suitably sized aquarium.

Keep apart

• Boisterous tank mates. Dartfish are easily intimidated by boisterous fish, and an intimidated firefish hides and misses meals.
• Other dartfish species. OATA says different species should not be mixed. That includes the red firefish, sold as the fire goby, which is an alternative to this fish rather than a companion for it.

Reef aquariums

Wikipedia notes that the Elegant Firefish is popular in reef aquariums and that firefish are commonly kept in nano reefs. In a reef, run the water to the corals' needs, as OATA advises for more sensitive species, and remember that corals may need brighter lighting than the firefish alone. Rockwork for corals doubles as cover for the fish, provided you leave bolt-holes open.

Before you buy any tank mate

OATA's standing advice is to consult your retailer before buying any dartfish, to make sure it will mix with your current fish, and its checklist asks you to research every species you are considering and confirm your final choices are all compatible. Add new fish slowly so the filter keeps pace, and watch the first few feeds after each addition to check that the firefish still comes out to eat.

One firefish, a pair or a group?

Most keepers will do best with a single Elegant Firefish. These are the points that make more than one a considered decision rather than a default.

• In the wild: FishBase records it as often found in pairs and monogamous.
• In groups: OATA notes that some dartfish can live together in groups, especially when younger.
• In a small space: Wikipedia warns that firefish kept in confined quarters may squabble over territory.
• Sexing: OATA says dartfish are difficult to sex unless they are in breeding condition, and no sex is guaranteed on this listing.
• Space: OATA's 60 litre recommendation is for one individual, and the aquarium needs to be larger for more than one.

A worked decision

Suppose you have a 60 litre marine aquarium. That meets OATA's recommendation for one dartfish, so plan for a single firefish with calm companions. Now suppose you run a much larger reef with long runs of rockwork and several separate bolt-holes, and you would like two. Because two fish bought together are not a guaranteed male and female, and firefish may squabble in confined quarters, give each fish its own cover well apart and be ready to separate them if one keeps the other from open water or food.

Buyer questions answered

How big does an Elegant Firefish get?

FishBase records a maximum length of 9.0 cm total length for this species, and Wikipedia gives the same 9 cm. Plan the aquarium around that adult length rather than the size of a newly arrived fish.

What size aquarium does it need?

OATA recommends at least 60 litres for one dartfish, with a larger aquarium if you keep more than one or add other species. It also needs rockwork with crevices and overhangs, moderate flow and a secure lid, because dartfish will jump, especially if startled.

How many Elegant Firefish should I keep together?

Most keepers should plan for one. Wild fish are often found in pairs, but dartfish are difficult to sex outside breeding condition and firefish may squabble in confined quarters, so keep two only in a larger aquarium with separate bolt-holes.

Is it suitable for beginners?

OATA describes dartfish as usually undemanding of water chemistry, which helps. The fish still needs a matured marine filter with zero ammonia and nitrite, a lid, plenty of cover and calm tank mates, so it suits a keeper who can provide all four.

What does an Elegant Firefish eat?

In the wild it eats zooplankton, especially copepods and crustacean larvae. In the aquarium, OATA's dartfish advice is prepared pellets or flake plus small frozen foods such as copepods, enriched brine shrimp and finely chopped mysis, fed twice a day in amounts eaten within a few minutes.

What temperature and pH does it need?

Keep it at 24–26°C, pH 7.9–8.3 and salinity 1.020–1.025, with ammonia and nitrite at zero and nitrate below 50 mg per litre. These are OATA's broad guidance for dartfish and jawfish, not a species-specific optimum.

Is the Elegant Firefish aggressive, or does it nip fins?

Wikipedia describes it as relatively docile and says it will not attack tank mates in a suitably sized aquarium, though firefish kept in confined quarters may squabble over territory. It is more likely to be bullied than to bully.

What kinds of fish can it live with?

OATA suggests calm fish that let dartfish come out to feed, such as cardinalfish or small gobies. Avoid boisterous tank mates and other dartfish species, including the red firefish sold as the fire goby.

How does an Elegant Firefish arrive alive in the UK?

Film a continuous unboxing video from the moment the parcel is still sealed, open and inspect it the same day, then float the bag for 20–30 minutes before releasing; the Live Arrival Guarantee needs that video. It travels hand-bagged in pure oxygen in an insulated poly box, carried by a licensed live-animal courier.

References

• FishBase: Nemateleotris decora, for family placement, range, depth, wild habitat, diet, pairing and maximum length.
• Wikipedia: Elegant firefish, for common names, description, the N. exquisita question and aquarium behaviour.
• Ornamental Aquatic Trade Association: how to look after jawfish and dartfish, for water values, set-up, maintenance, feeding, health, compatibility and breeding.
• RSPCA: aquarium environment, for filtration and the nitrogen cycle.