Ragfish

Where they come from

Ragfish are oddballs from the cold North Pacific. Think Japan and the Kurils across to Alaska and down the West Coast to California. Juveniles cruise near the surface and around jellyfish, adults slip deeper, hundreds of meters down, where the water stays cold and dim. They grow big and floppy, with soft, scaleless skin and a body that feels more like a thick towel than a typical fish.

Setting up their tank

Size and shape matter more than anything. Ragfish are pelagic drifters with clumsy steering. Straight runs and rounded corners keep them from face-planting.

• Tank style: circular or oval raceway. No sharp corners. A kreisel-style layout works well.
• Volume: 3,000-5,000 L for a sub-40 cm juvenile. Full-size animals are beyond home setups (20,000+ L).
• Temperature: 5-9 C. Pick a number and keep it steady.
• Salinity: 33-35 ppt. pH 7.9-8.2. Ammonia and nitrite at 0, nitrate as low as you can keep it.
• Oxygen: very high. Use strong aeration and big skimming.

Flow should be gentle, continuous, and circular. You want them cruising without having to fight. I aim for 2-3 tank turnovers per hour with diffused returns aimed to create a slow gyre.

Keep the interior smooth and bare. No rock piles or sharp gear. Use guarded intakes and pad any potential bump zones with smooth acrylic or EPDM. Bare bottom is easiest to sanitize.

Lighting stays dim and cool-toned. Short photoperiod, 8-10 hours max. They come from gloom. Bright lights make them spook and rub their noses raw.

Filtration has to be oversized. Big skimmer, generous mechanical prefilter, and bio media with tons of surface area. A reliable chiller (or two in parallel) is non-negotiable. Insulate the tank and plumbing to keep the chiller from working itself to death.

What to feed them

Wild ragfish pick at gelatinous plankton as kids and shift to fish and squid as they get larger. Getting a new one to take prepared food can be slow, but the current is your friend.

• Starter foods: live or freshly killed small baitfish, soft-bodied shrimp, squid strips cut into fluttery ribbons.
• Staples once eating: chopped squid, silversides, sand lance, pollock pieces, capelin, krill, large mysis. Rotate proteins.
• Supplements: soak meals in a broad marine vitamin and add thiamine if you use a lot of smelt/capelin (thiaminase risk).

Feed small, neutrally buoyant pieces into the circular flow so they drift past the mouth. Tongs help, but avoid poking their face. Start with 1-2 light feeds daily for juveniles. As they settle, every day or every other day is fine. Avoid stuffing them with oily fish all the time; ragfish pack fat easily and get sluggish.

How they behave and who they get along with

Think slow, pliable, and a little clueless near walls. They cruise midwater, rarely pick fights, and spook at sudden movement. They are opportunistic with anything bite-sized, though, and that big mouth will surprise you.

• Best kept alone. Mixing coldwater pelagics sounds fun until someone eats someone.
• If you must try a companion, choose similar-size, non-nippy, slow swimmers from the same temperature range, and be ready to separate fast.
• Avoid fast, aggressive feeders. The ragfish will miss meals and stress out.
• Absolutely no small fish or inverts you care about. They are fair game.

Breeding tips

There are no captive breeding reports for ragfish. In the wild they are believed to spawn pelagically in deep, cold water, and larvae drift with the plankton. Sexing them is not straightforward, and they do not show pairing behavior in tanks. File this under not happening in home aquaria.

Common problems to watch for

• Face and snout abrasions: usually from bumping walls. Round the flow, pad impact spots, keep lighting low. Minor scrapes heal if water is pristine.
• Not eating: often too bright, too warm, or too much flow. Fix environment first, then tempt with squid ribbons or live offerings.
• Parasites and worms: wild-caught fish often carry them. Do a long, calm quarantine and use targeted dewormers at conservative doses. Scaleless skin is sensitive to copper and harsh dips.
• Bacterial sores in cold water: Vibrio/Pseudomonas can take hold on damaged skin. Keep oxygen high, temperature stable, and consider vet-guided antibiotics if lesions spread.
• Gas bubble issues: look for tiny bubbles on fins/skin or odd buoyancy. Reduce microbubbles, add degassing, check pump seals and chiller plumbing for leaks pulling in air.
• Thermal stress: even a couple of degrees up will make them lethargic and disinterested in food. Use redundant chillers and alarms.