Blunt scalyhead

Where they come from

Blunt scalyheads are Antarctic notothenioid fishes living on the continental shelf around rock and rubble, usually under or near pack ice. Water is near freezing year-round, and they have antifreeze proteins in their blood to deal with it. Picture a slow, bottom-hugging ambush hunter sitting on the seafloor while brash krill clouds drift by.

Setting up their tank

Plan a dedicated cold marine system. They do not tolerate warmth. Mine lived at 0.5 C with brief dips just below zero, and anything above 3-4 C made it noticeably stressed and off food.

• Tank size: 120 gallons or larger for a single adult (they reach roughly 20-30 cm). More water makes temperature and nitrogen management less stressful.
• Temperature: -1 to +2 C. Use a commercial-grade chiller that can hold near-freezing temps continuously.
• Salinity: 34-35 ppt (1.026-1.027 SG at 0-2 C). Keep it steady.
• pH: 8.0-8.3. Alkalinity 7-9 dKH. Test at the actual tank temperature.
• Aquascape: Flat stones and cobble with a few caves. Soft sand or fine gravel so they can settle comfortably.
• Flow: Moderate, mostly along the bottom. They are bottom sitters, so avoid blasting them.
• Filtration: Oversized biofilter and skimmer. Cycle the tank at the target temperature.
• Lighting: Dim to moderate and diffuse. They dislike sudden, bright shocks.

Cold water slows nitrifying bacteria. My cycle took twice as long as a warm marine tank, and the biofilter matured slowly. Be patient and stock very lightly.

• Run a controller with two temperature probes and an audible alarm.
• Keep a spare pump rated for near-freezing water.
• Use sealed LEDs; condensation will destroy open fixtures.
• Have towels handy. You will get rime and drips on the lid and plumbing.

What to feed them

They are slow ambush predators that take meaty foods. Most will ignore flakes and pellets. I had best luck target feeding with tongs so the food reached the bottom before scavengers got it.

• Primary staples: frozen mysis, marine amphipods, chopped marine fish (e.g., silversides), clam, mussel, squid strips.
• Starter live foods (to get new fish eating): live shore shrimp, small crabs, amphipods from a cold refugium.
• Supplements: soak in a broad-spectrum vitamin a couple times a week.

Feed 2-3 times per week. At these temperatures their metabolism is slow. Watch the belly profile and adjust. Remove leftovers within 10 minutes to keep nutrients in check.

How they behave and who they get along with

Think patient, not shy. They perch, watch, and make quick darts to grab prey. They do not have a swim bladder, so you will see a lot of bottom time and short repositioning bursts rather than cruising.

• Temperament: Generally calm but very predatory toward anything bite-sized.
• Tankmates: Realistically, keep them alone. Almost no commonly available species can handle 0-2 C.
• Cleanup crew: Hard to source true coldwater inverts legally. Plan to siphon detritus yourself.
• Multiple scalyheads: Possible in very large tanks with line-of-sight breaks, but have a backup plan to separate.

Breeding tips

Hobby breeding is basically undocumented. Some related notothenioids lay demersal eggs and show nest guarding, but expect this to be a research-grade project.

• Pairing: You would need compatible adults collected from the same region and season.
• Cues: Strong seasonal photoperiod and very cold water are likely required. Many Antarctic fishes spawn late winter to spring.
• Nest: Provide flat stones and protected crevices for potential egg deposition.
• Larvae: Almost certainly pelagic and tiny. You would need live coldwater plankton cultures (copepods) at near-freezing temps. That is the hard part.

Common problems to watch for

• Heat creep: Pumps, room heat, and lights can nudge temps up. Use insulated plumbing and sealed lids.
• Stalled biofiltration: At 0-2 C, nitrification is sluggish. Over-filter, stock lightly, and test often.
• Overfeeding and fatty liver: They look hungry because they sit still. Keep portions small and varied.
• Parasites from wild-caught fish: Quarantine at the same cold temperature for 4-6 weeks. Many meds behave differently at near-freezing temps.
• Injuries from panic dashes: Pad sharp rock edges and avoid sudden light changes.
• Copper and hyposalinity: Risky here. I avoid both with Antarctic fishes; focus on QT, observation, and targeted antibiotics if needed.