Sea goblin

Where they come from

Sea goblins (Inimicus didactylus) are Indo-Pacific ambush predators. You find them on sandy and muddy flats, seagrass edges, and rubble zones from the Red Sea across to Japan and down to northern Australia. They bury themselves and

look like a lump of reef until a snack wanders by. Those pectoral "fingers" are real - they use them to "walk" and probe the bottom. They are venomous, very still, and very good at disappearing in plain sight.

Tank setup

Give them floor space, not height. A 40 breeder (36 x 18 in / 90 x 45 cm) works for one. Bigger is better if you want tankmates.

• Substrate: 2-3 inches of fine aragonite sand. Skip crushed coral and sharp sands; they bury and can scrape themselves.
• Aquascape: Open sand patch front and center. Low rock arches or rubble piles around the edges. Keep rockwork stable.
• Flow: Gentle to moderate with a calm zone. They like to sit out of the blast.
• Lighting: Dim to moderate. They are crepuscular and appreciate shaded spots.
• Lid: Tight-fitting. They are not jumpers, but lids keep food odors in and accidents out.
• Filtration: Strong skimmer and regular mechanical filtration. Feeding is messy.
• Parameters: 76-80 F (24-27 C), 1.023-1.026 SG, pH 8.1-8.4, low ammonia/nitrite, keep nitrate reasonable (<20-30 ppm).

What to feed them

They are ambush predators that learn tongs fast if you are patient. Start with movement, then switch to non-live once they associate the tongs with food.

• Good foods (marine-origin): pieces of shrimp, squid, scallop, silversides, sand eels, lancefish, and live or thawed saltwater shrimp (grass/ghost shrimp acclimated to salt).
• What to skip: goldfish, rosy reds, and feeder guppies. Wrong fats and thiaminase issues long-term.
• Size: bites no larger than the width of the fish's eye-to-eye distance. They can swallow huge prey, but that is how you get regurgitation and injuries.
• Vitamins: soak frozen foods in Selcon or a marine vitamin a couple times a week.

Feeding schedule that has worked for me: juveniles every 2 days, adults every 3-5 days. Watch girth behind the head - a slight, smooth bulge is fine; bowling-ball shape means cut back.

How they behave and who they get along with

Calm, sneaky, and mostly motionless until feeding time or dusk. They will eat any fish or shrimp that fits in their mouth, so plan tankmates by size, not attitude.

• Safe bets: large, non-nippy fish that ignore bottom dwellers (bigger foxfaces, tangs, some peaceful angels), large cardinalfish, some eels. Another scorpionfish can work in a big tank with lots of space and sight breaks.
• Risky: triggers, puffers, big wrasses, and curious hawkfish - they poke and may get stung or harass the goblin.
• Inverts and corals: corals are fine; mobile inverts are snacks. Hermits and snails are usually OK; ornamental shrimp are not.
• Reef note: they sit on corals if placed poorly. Give them a sand pad so they do not bulldoze your frags.

Breeding tips

Not something hobbyists are pulling off at home. Sexing is not obvious, courtship is poorly documented, and they likely release eggs that drift. I have not seen a verified captive spawn for this species in standard aquaria.

If you want to experiment in a very large lagoon-style system: condition two adults on rich foods, give them lots of space and gentle flow, run seasonal light and temp swings, and keep a separate larval setup ready. Just set expectations low and enjoy the fish for what it is.

Common problems to watch for

• Refusing food after shipping: start with live saltwater shrimp, then wean. Keep the room quiet and lights low for the first week.
• Sand abrasions: shows up as pale scrapes on the flanks. Usually linked to sharp substrate. Swap to finer sand and keep water clean.
• Overfeeding and regurgitation: too large a meal or feeding too often. Smaller, spaced-out feedings fix this.
• Eye cloudiness: often water quality or mechanical irritation from rough sand. Improve filtration and check flow/sand choice.
• Parasites (flukes, Cryptocaryon): quarantine new arrivals. Prazipro works well for flukes. Use copper only if you are comfortable testing daily; appetite can drop under copper.
• Handling injuries: nets and rough moves break fin rays. Always use a container for transfers.
• Powerhead accidents: not common, but cover strong intakes, especially in small tanks.