Eckstrom's topknot

Where they come from

Eckstrom's topknot (Zeugopterus regius) is a cold-temperate flatfish from the Northeast Atlantic. Think rocky coastlines, kelp-covered reefs, and pier pilings from the British Isles down toward Iberia. They hug vertical rock faces and overhangs, often sitting upside down like little pancakes waiting for a snack to wander past.

Setting up their tank

Give them height and rockwork, not just floor space. They perch on walls and under ledges more than they sit on sand. A single adult does well in 250 L/65+ gal, but bigger is nicer if you want tall rock faces and calm zones.

• Temperature: 10-16 C (50-61 F). They handle brief bumps to 18 C, but keep it cool.
• Salinity: 1.025 specific gravity (1.023-1.026 is fine).
• pH: 8.0-8.3, alkalinity 8-10 dKH.
• Nitrate: under 20 ppm, closer to 5-10 is safer long term.
• Flow: moderate with some slack water pockets so they can rest.
• Lighting: dim to moderate. They do not love bright reef lights.

Stack stable live rock or dry rock to make ledges, caves, and at least one tall, mostly vertical face. Slate tiles siliconed to the back or sides work great and are easy to clean. Sand is optional; if you use it, go fine and clean. Avoid sharp lava rock that can scrape their skin.

Run a skimmer and keep oxygen high. Cold water holds more O2, but they still appreciate surface agitation. Use a tight lid; they are not big jumpers, but any fish can bolt during maintenance.

What to feed them

They're ambush predators with a lazy streak. Most new arrivals only respond to movement at first. Start with live foods, then wean to frozen. Feed at dusk or with room lights off; they get braver in low light. Use tongs and place the food right in front of them.

• Starter foods: live river shrimp, amphipods, live mysis, small shore crabs (soft-shelled), glass shrimp.
• Frozen options once they catch on: PE mysis, krill (not as a sole diet), chopped raw prawn, squid strips, sand eel/lancefish pieces, marine fish fillet.
• Supplements: add a marine vitamin/HUFA soak once or twice a week.

Juveniles do best with small daily feeds. Adults are fine every 2-3 days. Remove leftovers within a few minutes so they do not rot in crevices.

How they behave and who they get along with

Calm, cryptic, and mostly nocturnal. They spend hours perched on rock faces, then make a quick lunge at passing prey. They ignore most fish that ignore them, but anything bite-sized is a snack. They are not reef safe around ornamental shrimp and small crabs.

I keep mine either alone or with other cool-temperate, mellow fish that do not pick at fins. Boisterous wrasses and fast feeders steal all the food and stress them out.

• Better choices: larger temperate gobies/blennies that mind their own business, sedate sculpin-type fishes, peaceful dither fish from similar temps.
• Risky/avoid: warm-water species, nippy wrasses, triggers, groupers, big crabs/lobsters, decorative shrimp, tiny fish under about 6-7 cm.

Breeding tips

Realistically, this is not a home-aquarium project. Topknots spawn pelagic eggs in spring with increasing day length and cool water. The larvae are planktonic and need specialized live foods (copepods) and gentle circular flow like a kreisel setup. I have not seen a confirmed home breeding of Z. regius.

Common problems to watch for

• Heat creep: summer rooms push tanks over 18 C. Use a chiller and monitor with a reliable controller.
• Hunger strike: many new fish ignore dead food. Offer live first, feed at dusk, and train with tongs. Patience wins.
• Flukes/skin issues: wild-caught fish often carry flukes. Praziquantel works well. Avoid copper on scaleless/cuticle-heavy fishes like this.
• Bacterial sores from scrapes: keep water clean, treat early with a broad-spectrum antibiotic in QT if you see fuzzy patches or ulcers.
• Food theft by tankmates: target feed and use a feeding stick so the topknot actually gets its share.
• Rubbing on rough rock: they press against surfaces all day. Use smoother faces and check for sharp edges.

If you commit to cool temps, dim light, and the feeding routine, Eckstrom's topknot is a fascinating display fish. Low drama, lots of personality once it settles, and a great excuse to build a rocky temperate setup.