Obscure spiny eel

Where they come from

Obscure spiny eels are Macrognathus, so think lowland Asia: slow rivers, floodplains, and backwaters with soft bottoms, leaf litter, and lots of places to disappear. Seasonal rains swell the water and scatter food, which explains a lot about how they behave and eat in our tanks.

Setting up their tank

Plan for a stealthy, bendy fish that likes to burrow. Mine topped out around 7-8 inches. A single does well in a 30-40 gallon with a long footprint. If you want two or three, go 55+ and pack in the hiding spots.

• Substrate: fine sand, 2-5 cm deep. Skip gravel. They dig, and rough edges rub their bellies raw.
• Hides: driftwood tangles, leaf litter, caves, PVC elbows, dense plants (real or fake). They relax when every direction has a bolt-hole.
• Filtration: steady but not blasting. They appreciate clean, oxygenated water without a powerhead hurricane.
• Water: 75-82 F (24-28 C), pH 6.2-7.5, soft to moderately hard. Keep nitrates low with regular changes.
• Lighting: on the dim side. Floating plants help.
• Intakes: cover with sponge pre-filters so they do not wedge in while nosing around.

What to feed them

They are nose-driven hunters. New arrivals often refuse pellets at first. Start with wriggly or smelly foods, then work your way to frozen and, maybe, sticks later.

• Go-to foods: live blackworms, chopped earthworms, mosquito larvae, frozen bloodworms, frozen mysis, chopped prawn.
• Transition trick: offer thawed frozen on long tweezers at dusk and move it a little. They will strike movement.
• Long term: some take soft sinking carnivore pellets after a few weeks. Mix a few in with frozen as they learn.
• Feeding time: evening or lights-out. They are braver and eat more once the tank quiets down.

How they behave and who they get along with

Calm but opportunistic. They ignore anything too big to swallow and will absolutely snack on tiny fish and shrimp if they can ambush them.

• Good company: peaceful mid-water fish that are at least 1.5x the eel's mouth width. Think medium rasboras, rainbows, peaceful barbs, larger tetras, gouramis.
• Questionable: very fast bottom feeders (loaches) that outcompete them at dinner, or territorial cichlids that claim the floor.
• Avoid: nano fish, small shrimp, fin-nippers, and bullies. Also avoid other sand-burrowers unless the tank is large with many hides.

You can keep a small group if the tank is big and the scape breaks line of sight. Mine were more visible in a trio. Give each eel at least two private hides and feed in multiple spots.

Breeding tips

Home breeding is rare. They are seasonal spawners that scatter eggs during wet-season cues. Farms use hormones. If you want to try the natural route, you need space and patience.

• Condition heavy on worms and high-quality frozen for a few weeks.
• Simulate a monsoon: gradually drop water level and raise temp a bit, then do a large, slightly cooler, soft-water change and increase flow.
• Provide dense plants or spawning mops near the surface and fine-leaf cover below.
• Males tend to be slimmer; females round out with eggs. After a chase, eggs scatter and stick to plants.
• If eggs appear, pull adults. Fry start tiny; feed infusoria then freshly hatched baby brine. Expect losses.

Common problems to watch for

• Scrapes and fungus from rough substrate or decor. Sand fixes most of this.
• Internal worms from wild-caught stock. A round of levamisole or flubendazole in quarantine helps.
• Refusing food in bright, busy tanks. Dim the lights, feed after dark, offer live or very fresh frozen.
• Ich and medication sensitivity. They are scaleless, so start at half-dose with dyes or formalin, or use heat/salt carefully and monitor.
• Escape attempts after big water changes or sudden noise. Double-check the lid during maintenance.
• Getting outcompeted. Target-feed with tongs or a turkey baster right to their nose.