Smalleye conger
Gnathophis microps
The Smalleye conger features a slender, elongated body, pale brown coloration, and distinctive small eyes, aiding in its deep-sea camouflage.
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About the Smalleye conger
Gnathophis microps is a deepwater marine conger eel from off Western Australia, and its little eyes make a lot of sense once you realize it lives way down around 200-320 m. Cool fish on paper, but its deep, cold-ish habitat means it is basically not a realistic home-aquarium species (think public-aquarium level life support).
Quick Facts
Size
36.5 cm (14.4 inches) TL
Temperament
Semi-aggressive
Difficulty
Expert
Min Tank Size
180 gallons
Lifespan
unknown
Origin
Eastern Indian Ocean (Western Australia)
Diet
Carnivore - small fishes and benthic invertebrates (typical conger eel diet)
Water Parameters
6-14°C
7.8-8.4
8-12 dGH
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This species needs 6-14°C in a 180 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give it a long, covered tank with a tight lid and taped gaps - smalleye congers are escape artists and will go exploring at night.
- Build the scape around burrowing: 3-6 inches of fine sand plus a few snug PVC elbows or rock tunnels; sharp rock and coarse crushed coral will shred their skin.
- Keep salinity steady at 1.024-1.026 and run heavy oxygenation and flow; they sulk fast in low O2 and get twitchy if pH swings (aim 8.1-8.4).
- Feed after lights-out with tongs: thawed silversides, squid, shrimp, and marine fish flesh work well; start with smaller strips so they dont spit it and foul the tank.
- Skip delicate tankmates and anything small enough to fit in its mouth; tough midwater fish can work, but avoid slow bottom perchers and small gobies/blennies.
- Treat it like a predator for filtration: big skimmer, aggressive mechanical cleanup, and dont let uneaten chunks sit in the sand or youll get a nasty ammonia spike.
- Watch for abrasions and mouth damage from rockwork and rough feeding; once the skin gets scraped, bacterial infections can snowball fast in warm marine systems.
- Breeding in home tanks is basically a no-go - they are deepwater spawners and adults dont do the cute pair-bond thing, so dont buy two thinking youll get babies.
Compatibility
Good Tankmates
- Other eel-ish, non-nippy tank mates like morays or snake eels that are similar size and temperament (give everyone their own caves and keep them well-fed)
- Medium-to-large, sturdy reef-safe-ish fish that can hold their own and are not bite-sized - think tangs and rabbitfish (they ignore the conger, and the conger usually ignores them)
- Bigger wrasses that are confident and fast (Halichoeres-type, bird wrasse, etc.) - quick enough to avoid a surprise lunge and not usually interested in picking on eels
- Large angelfish (Pomacanthus-type) if your setup is fish-only or you are not married to delicate inverts - they are bold, not snack-sized, and typically not bothered by an eel
- Hawkfish and other chunky perchers that are not tiny (flame hawk, longnose hawk) - they tend to stick to rockwork and the conger mostly cruises the bottom
- Tough bottom neighbors like large squirrelfish/soldierfish (not small ones) - they are nocturnal too and usually coexist fine as long as you are not underfeeding
Avoid
- Small fish you would not mind losing - chromis, small damsels, tiny cardinals, small gobies and blennies (if it fits in the conger's mouth, it is food sooner or later)
- Shrimp and small crabs - cleaner shrimp, peppermint shrimp, emerald crabs (they are basically live snacks for a conger in most tanks)
- Slow, long-finned, easy-to-grab fish like lionfish and long-fin butterflies (the conger is a night hunter and those make tempting targets)
- Super aggressive brawlers that will harass or bite at the eel's face - big triggers, large dottybacks in smaller tanks, mean damsels that claim the whole rock pile (stress and injuries add up)
Where they come from
Smalleye congers (Gnathophis microps) are offshore, bottom-oriented eels. You usually see them tied to deeper coastal slopes and sandy or rubble areas where they can disappear fast. The name fits - small eyes, lots of time spent in dimmer water and under cover.
In the hobby, the big challenge is that many arrive as bycatch or oddball imports, so you do not always get a clean backstory on collection depth, holding time, or what they have been eating. Assume it has had a rough trip and set up accordingly.
Setting up their tank
Think "secure eel bunker" more than show tank. This species wants tight hides, soft substrate, and zero escape routes. If you give it a calm, predictable setup, it will settle in and feed way faster.
- Tank size: I would not bother under 125 gallons, and bigger is genuinely easier because waste builds up fast with eel feeding.
- Substrate: fine sand is your friend. They like to nose into it, and sharp gravel can scrape them up.
- Hiding: PVC elbows/pipe sections (2-3 inch or larger depending on the animal) buried and disguised with rock work. Give at least two hides so it can choose.
- Rockwork: stable and sitting on the bottom glass, not on top of sand. Eels dig and will undermine stacks.
- Lid: tight-fitting, weighted, and sealed around plumbing and wires. If a pencil fits, an eel fits.
- Flow and oxygen: moderate flow and strong gas exchange. A good skimmer helps a lot.
- Filtration: oversize everything. Eels are messy, and uneaten meaty food can nuke water fast.
Escape prevention is not optional. Cover overflow teeth, seal gaps at the back of the lid, and secure any mesh. I have found eels dried behind tanks from openings I would have bet money were too small.
Keep lighting on the subdued side, at least at first. If you have bright reef lighting, build shaded zones with overhangs and caves so it can feel hidden during the day.
Water parameters are the usual marine targets, but stability matters more than chasing numbers. Sudden swings in salinity or temperature hit eels hard, especially fresh imports.
What to feed them
They are meat-eaters, and they learn routines. Once they associate your feeding stick with food, life gets easier. Until then, patience wins.
- Good staples: thawed marine-origin foods like silversides, squid, shrimp, clam, and chunks of marine fish.
- Rotate foods: variety helps prevent nutritional gaps and keeps them interested.
- Use a feeding stick/tongs: keeps your fingers safe and lets you place food right at the hide entrance.
- Portioning: smaller pieces more often beats one huge chunk. Think 2-3 times a week for adults, more frequent for smaller individuals.
- Vitamins: I soak food occasionally in a marine vitamin supplement, especially during the first month.
Skip freshwater feeder fish and fatty freshwater items long-term. They can cause nutrition issues and messy water. Stick to marine-based foods.
If it refuses food at first, try feeding after lights-out, and keep the room quiet. Some individuals will only take food once they feel the tank is "theirs". Also, do not leave uneaten meaty food in there - pull it after 10-15 minutes.
How they behave and who they get along with
Most of the time they are a "head in a cave" animal that comes alive at dusk. The problem is not constant aggression, it is the fact they will absolutely eat what fits.
- Good tankmates: sturdy, non-nippy fish too large to swallow (bigger angels, larger tangs, robust wrasses), and generally peaceful but confident species.
- Avoid: small fish, shrimp, crabs, and anything you would be sad to lose. Also avoid fin-nippers that stress the eel into hiding and refusing food.
- Multiple eels: possible in a big tank with multiple hides, but introductions can be tense. If you try it, do it with similar size individuals and lots of cover.
If you never see it, that is not automatically a problem. Watch for signs like steady body weight, clean skin, and consistent feeding response rather than daytime visibility.
During feeding, they can get excitable and clumsy. Keep rock edges smooth where it launches from hides, and do not hand-feed. A startled eel can bite by mistake, and it is not a fun lesson.
Breeding tips
Breeding this species in home aquariums is basically not a realistic goal right now. Many conger-type eels have complex life cycles with pelagic larval stages (leptocephalus larvae) that drift in the open ocean. Even if a pair spawned, raising larvae would be a whole separate project that is not really solved for most eels.
If you want to try something breeding-adjacent, focus on long-term conditioning: stable water, varied marine foods, and a calm tank. Even getting one to live for years and feed reliably is an achievement with this group.
Common problems to watch for
- Escapes: the number one killer. Re-check the lid after every maintenance session.
- Refusing food: common right after import. Reduce stress, feed at night, offer different textures (soft squid vs firm fish), and keep hands out of the tank during attempts.
- Injuries from rockwork: scrapes on the head and flanks happen if they wedge into sharp holes. Smooth caves and PVC hides prevent a lot of this.
- Parasites: wild-caught eels can come with external parasites. Watch for flashing, rapid breathing, or cloudy eyes.
- Ammonia spikes: caused by overfeeding or missed leftovers. Eels are forgiving until they are not - test after big feedings early on.
- Copper sensitivity concerns: many scaleless or reduced-scale fish handle meds differently. If you need treatment, research carefully and consider hospital setups rather than dosing the display.
Quarantine is worth the hassle with these. A simple bare-bottom tank with PVC hides and a tight lid lets you observe feeding and treat issues without nuking your display.
One last practical thing: plan your maintenance around the eel, not the other way around. Move slowly, keep the lid closed as much as you can, and always know where its head is before you put hands near a cave. That habit saves you from bites and saves the eel from panic flights.
Similar Species
Other marine semi-aggressive species you might be interested in.
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