Harelip cusk

Where they come from

Harelip cusk (Ophidion lagochila) is a sand-hugging cusk-eel from the western Atlantic. Think quiet coastal shelves, bays, and sandy patches near grass beds. They spend daylight buried or tucked into the sand and get active at dusk. Mine came in as a Gulf/Caribbean bycatch fish and acted exactly like a shy, nocturnal ambush hunter from a flat, sandy world.

Setting up their tank

Plan the tank around sand and security. These guys are built to slip into fine substrate and disappear. If they do not feel like they can hide, they just won't settle or eat well.

• Tank size: 55 gal minimum for a single, 75+ gal for a pair. They need floor space more than height.
• Substrate: 3-5 inches of fine aragonite sand. No crushed coral or sharp gravel - it scuffs their skin.
• Hides: Add PVC elbows, smooth rock caves, and sand trays they can burrow into. Keep layouts low and open so they can snake around without scraping.
• Flow and light: Moderate flow, dim lighting. They relax a ton under subdued lights.
• Lid: Tight, gap-free cover. They are expert jumpers when startled.
• Water: 1.024-1.026 SG, 72-76 F, pH 8.0-8.3, low nitrate. Good oxygenation helps them stay active at night.

What to feed them

They are meaty-food hunters. Most new arrivals ignore pellets and flakes. Start with movement and smell, then work toward tongs and eventually still food.

• Starter foods: live blackworms, live ghost shrimp, or freshly thawed mysis moved with tongs.
• Staples: frozen mysis, chopped krill, finely diced shrimp, clam, squid, and fish flesh. Mine went nuts for soaked LRS-style blends once he settled.
• Training: Wiggle food with long tongs at dusk. Once they strike, keep the routine at the same time each night.
• Supplements: Soak a couple feeds per week in vitamins and HUFA (Selcon-style) to keep weight and color.
• Frequency: Small meals 4-6 times per week. Skip a day now and then to keep water clean.

How they behave and who they get along with

Shy by day, cruisers by night. They are sand weavers, not open-water swimmers. Usually peaceful with fish they cannot swallow, but they will absolutely snack on tiny fish and shrimp that fit in their mouth.

• Good tankmates: peaceful to moderately assertive fish like larger gobies, blennies, fairy wrasses, tangs, and docile basslets. Avoid hyper-aggressive bullies.
• Not good: small ornamental shrimp, tiny gobies, sexy shrimp, and nano fish. Also avoid dottybacks and big hawkfish that harass cave dwellers.
• Social: Best kept singly unless you can source a known pair and have a big footprint. Two random individuals may bicker in tight quarters.
• Activity window: Most feeding and exploring happens at dusk. Give them a calm evening routine.

Breeding tips

This is still a long shot in home tanks. Wild cues likely involve season, temperature shifts, and night activity in sandy areas. Sexing is not obvious, and pairing strangers can end in silent standoffs.

• If you want to try: run a large system with multiple sand beds, several cave clusters, and very low evening light.
• Mild seasonal changes: a small temp swing across the year (2-3 F), and slightly heavier feeding ahead of your simulated spring.
• Group only if your tank is big enough to let them avoid each other. Add all candidates at once to reduce territory claims.

Common problems to watch for

• Refusing food: Very common early on. Dim the lights, feed at dusk, and use moving, smelly foods. Give them sand to hide in first, then worry about training.
• Scuffed snouts and abrasions: Caused by coarse substrate or frantic glass-bumping. Use fine sand and add visual barriers along the bottom.
• Jumping: They launch during netting or loud noises. Keep a tight lid and be gentle during maintenance.
• Internal parasites: Look for stringy white feces and weight loss. Treat in quarantine with a food-soaked dewormer protocol.
• Medication sensitivity: They have delicate skin. Go easy with copper and formalin. If you must medicate, use test kits and the lower end of recommended ranges.
• Deep-caught stress: Some arrive with barotrauma or swim bladder issues. Choose specimens that are steady on the bottom and breathing normally.