No established common name

Where they come from

Xenisthmus nigrolateralis is a small Indo-Pacific wriggler that sticks close to sandy rubble on reef flats and gentle slopes. Think pockets of clean sand, scattered bits of coral rock, and shady ledges to duck under. They spend a lot of time half-hidden, watching for tiny critters moving over the sand.

Setting up their tank

Give them a matured reef with calm spots and lots of cover. I would not drop one into a brand-new build. A 20-30 gallon tank works for a single fish, but more water and footprint always helps with stability. They absolutely need fine sand to sift and dive into, plus rubble piles and small caves so they feel safe.

• Sand: sugar-fine to 1 mm. Aim for at least a couple of inches in some areas so they can dig and rest.
• Rockwork: broken-up rubble piles and low caves. Avoid towering, unstable stacks.
• Flow: moderate with sheltered pockets. Let food settle near their hideouts.
• Light: not fussy, but they appreciate shaded areas.
• Lid: tight mesh or solid cover. They can and will jump.
• Mature system: 6+ months old with visible pods makes life easier.

• Temp: 75-79 F (24-26 C)
• Salinity: 1.024-1.026
• pH: 8.0-8.4
• Nitrate: under ~20 ppm (stable and clean is the goal)
• Plenty of oxygen and stable salinity

What to feed them

Wild fish pick at tiny crustaceans all day. Getting them to take prepared foods can be the make-or-break step. Expect to start with live foods and work your way toward frozen.

• Great starters: live copepods (Tigriopus/Apocyclops), amphipods, live enriched brine (adult, not just nauplii), live mysis if you can source it.
• Transition foods: frozen mysis (chopped if large), calanus, finely chopped krill, Nutramar Ova, Masstick smeared onto rubble.
• Feeding style: target feed with a pipette near their hide. Briefly pause pumps so food settles right in front of them.
• Frequency: 2-3 small meals per day at first. They have small stomachs and like frequent snacks.
• Supplements: add a HUFA/vitamin soak (e.g., Selcon) a few times a week.

How they behave and who they get along with

Quiet, sand-hugging, and a bit secretive. They dash between cover, then hover and watch. They leave corals alone. They might snack on very tiny ornamental shrimp, so keep that in mind.

• Good neighbors: small peaceful gobies, dartfish (with a lid), pipefish/dragonface (only if you have a big pod supply), possum wrasses, small reef-safe blennies.
• Questionable: dragonets and other pod-hungry species. They compete for the same food base.
• Avoid: boisterous wrasses, dottybacks, hawkfish, larger predatory basslets, or anything that patrols the sand aggressively.

Breeding tips

Not many home reports out there. Likely cave or burrow spawners with the male guarding eggs, and then a planktonic larval stage that needs tiny live foods. It is a project for a dedicated setup rather than a display tank.

• Start with a bonded pair if possible. Provide multiple snug caves and PVC elbows partly buried in sand.
• Feed heavily with clean, varied foods to condition them.
• If they spawn, be ready to move larvae to a separate rearing tank with greenwater, rotifers, and copepods. Gentle circular flow (kreisel-style) helps.
• Larvae will likely need rotifers first, then copepods/Artemia as they grow. Frequent small water changes and stable light cycles help orientation.

Common problems to watch for

• Jumping: they spook easily. A tight lid with small mesh is non-negotiable.
• Refusing food: most common issue. Have live foods on hand before purchase.
• Bullying: fast, nippy tankmates keep them in hiding and off food.
• Parasites from import stress: ich/velvet can hit sand dwellers hard.
• Weight loss in quiet tanks: looks peaceful, but they may simply not be getting enough calories.