Marijke explains how to keep the beautiful firefish (Nemateleotris magnifica) successfully in your reef tank.
Firefish are among the most popular dartfish in the marine hobby, and it’s easy to see why. Members of the genus Nemateleotris combine spectacular colours with a peaceful nature and, when given suitable surroundings, are generally hardy aquarium residents.
They are also known for being shy. A firefish will usually spend much of its time hovering above or near its favourite hiding place, retreating into a burrow or rocky crevice whenever it feels threatened. This behaviour is perfectly normal, but it does mean that careful tank design and peaceful tankmates are important.
Did you know?
There are currently four recognised species of firefish, and all of them are available to marine hobbyists. The focus of this article is the more common species, Nemateleotris magnifica, but the care for all species is broadly similar. You can read more about each one here.
The purple firefish (Nemateleotris decora) is the second most commonly encountered species - Photo by Shutterstock
Setting Up a Firefish Aquarium
Adult firefish can reach around 9cm (3.5”) in length and are total homebodies, rarely venturing far from their chosen crevice. As such, a single specimen should do well in an aquarium of 60cm (24”) or larger – around the 75 litres (16 gal) mark – although I’d personally prefer to go for a slightly larger tank.
For a known pair, 80cm (31”) should be the absolute minimum, while unpaired fish would require a much larger footprint. Squabbles can erupt even among mated duos, and the losing party needs space to escape lest your ‘peaceful’ reef turns into a war zone.
Fishkeeping Top Tip
Stick to a single firefish unless your system is very large or you can obtain a confirmed pair. Although juveniles may live in small groups in the wild, adult firefish can be highly territorial towards their own kind. Putting two fish together and hoping for the best can result in one being relentlessly chased and eventually banished to the sump.
Photo by Shutterstock
Sexing Firefish
Obtaining a pair of firefish isn't always easy, mostly because telling males and females apart can be difficult.
The main reported external difference is the shape of the genital papilla. Females have a larger, more rounded papilla, while males have a smaller, less conspicuous and more pointed one. The problem is that these structures aren't always visible, particularly when you're looking at an active fish in a busy shop aquarium.
Even if you manage to identify a likely male and female, there is no guarantee they'll pair up once introduced to your reef tank. For this reason, the safest way to obtain a pair is to find a group of juveniles and look for two fish that have naturally paired.
Once a pair has formed, they will generally become territorial towards other members of their species, making it easier for an experienced retailer to identify the pair and separate them from the rest of the group.
This can take some patience. If you're looking for a pair, spend some time observing a group rather than simply choosing the fish that appear to be different sizes or sexes. Ask your local fish shop whether they have an established pair available – it could save you a lot of heartache (and potentially one very unhappy firefish).
Photo by Alex Bell
Keep a Lid On It
There's a lot of choice when it comes to choosing a reef aquarium, but your top priority for firefish should be to ensure it’s as close to hermetically sealed as possible.
Like many small species, firefish are known to be particularly skittish. They’re also called dartfish for a reason! In their panic, spooked individuals may travel upwards rather than into their hides. If the aquarium lacks a gap-free lid, this can result in an episode of what is known among aquarists as ‘carpet surfing’.
Decorations and Hiding Places
As we established, firefish like having a home to hide out in. So, we need to consider this when decorating your reef tank.
You must offer plenty of caves, crevices and hiding spots within the aquariums. Rocky caves and overhangs work great but you can also incide a few move in-ready PVC pipes.
The second most important box to tick is a generous layer of sandy substrate for your finned friend to construct its home in. They may opt to just make a home in one of the small holes within the rockwork, but as they are reported to burrow into the sand as well, it is best to provide them with the opportunity to do so if they wish.
Photo by Shutterstock
Although I haven’t yet found a way to completely stop them jumping out of the water, being able to retreat into a safe burrow whenever they feel threatened should at least make your firefish less prone to taking to the skies.
Fishkeeping Top Tip
Consider dimming the reef tank lights when first introducing your firefish. This helps them feel safe, meaning you won’t have to feel the guilt of hearing it plonk against the tank lid because ‘there was a scary shimmer’. Once your new addition has found or constructed a burrow and appears comfortable, you can turn the brightness back up.
Potential Tankmates
Like most small, peaceful reef species, firefish won’t appreciate being surrounded by big and boisterous tankmates, particularly not the kind that might nip at their twitchy, elongated dorsal fins.
Instead, they shine – and display their natural behaviour – in tranquil systems with friendly neighbours. Anything from chromis and cardinals to jawfish and mandarin dragonets should work. Just make sure it doesn’t look too much like a dartfish, or it might end up on the receiving end of a Nemateleotris’ territorial wrath.
Banggai cardinalfish - Photo by shutterstock
Common clownfish are another common tank mate for firefish, but clownfish can become surprisingly aggressive and territorial. So, keep this in mind and perhaps go for a slightly bigger reef tank if you plan on mixing the two.
One thing I particularly like about firefish is that they’ll also leave invertebrates alone. They’ll play nice with anything from shrimp to feather duster worms, so you don’t have to worry about your cleaning crew being harassed.
They are considered reef safe, too, so corals, clams and any other sessile organism that takes your fancy will be safe. However, note that anemones can predate on small, slow moving tank mates like firefish from time to time.
Related article: Back to Saltwater: starting simple with beginner corals.
Photo by Shutterstock
Feeding Firefish
Why do firefish spend hours hanging motionlessly – head up, tail down – above their burrows? Because in the wild, their food comes to them!
All dartfish, which firefish are a member of, are specialised zooplankton eaters. Having perfected the ambush hunting technique on a tiny scale, all they have to do is wait patiently for meals to drift by.
This bug-based diet is good news for us aquarists, because it means our firefish will happily gobble up all the standard frozen reef fare you can offer. Just don’t think a single serving of Mysis a day will cut it, as firefish bodies are adapted to a constant trickle of food so small, regular feeding are needed. For the best results, feed small portions of frozen and prepared foods at least twice a day (preferably three or four times).
I also highly recommend offering some live food whenever you can. Put that refugium to work growing tasty pods – your firefish will thank you, and you’ll get to observe their natural feeding habits as an added bonus.
If you keep a busy mixed reef, keep an eye on your firefish to make sure it’s getting enough to eat. Bold tankmates can outcompete them easily and they can slowly starve, losing body condition.
Related article: The coolest nano fish - flaming prawn goby.
Finish Off Your Beautiful Reef
Firefish thrive in reef aquariums when their basic needs are met: peaceful tankmates, secure hiding places, regular small meals and, above all, a tight-fitting lid.
They have no particularly unusual water-parameter requirements, are widely available in the marine aquarium trade and remain relatively affordable compared with many of the more specialised reef fish.
Give a firefish the right environment and you’ll be rewarded with one of the reef hobby’s most elegant little fish – hovering above its burrow, waiting patiently for its next meal.