Royal codling

Where they come from

Royal codling show up along the western Atlantic, mostly off Brazil down toward Argentina. They hang out deep over sand and mud on the continental shelf and slope, nosing around with that little chin barbel at dusk and through the night. Think cool, dim, and quiet rather than reefy and bright.

Setting up their tank

Plan a coldwater, big-footprint system. They are soft-bodied, fairly long fish that like to wedge into a cave, then explode out for food. Give them room and stable, cool water.

• Volume - 180+ gallons for a single adult. More is better. Large footprint beats tall height.
• Temperature - 12-18 C. A chiller is not optional.
• Salinity - 1.025-1.027 SG.
• pH - 8.0-8.3. Alkalinity 8-10 dKH.
• Oxygen - very high. Strong surface agitation and oversized skimmer.
• Nitrate - try to keep under 20 ppm. Ammonia and nitrite should be 0.

Use a soft sand bed so the belly does not get scratched. Rockwork should be nailed down to the glass and absolutely stable. Add at least one hide sized like a burrow: 4-6 inch PVC elbows or big caves with only one or two entrances work well.

Lighting should be dim. I keep mine on a short, low-intensity schedule. They relax under blue light and will feed more reliably at dusk.

Flow can be moderate overall, but keep it gentle near the bottom so they can rest. Point powerheads upward for gas exchange.

Quarantine is a must. Match temp and salinity, dim the lights, and move them out of shipping water quickly. I dose an ammonia binder in the bag on arrival and drip for salinity only to avoid warming the fish during acclimation.

What to feed them

They are ambush predators that go crazy for meaty foods. Getting them onto tong-fed prepared foods makes life easier.

• Good staples - squid strips, raw shrimp, scallops, chopped marine fish like pollock or mahi, lancefish/sand eels.
• Occasional - mussel meat, krill, clam. Soak in vitamins once or twice a week.
• Avoid as a main food - oily, thiaminase-heavy fish like smelt or herring. Fine sometimes, not the backbone of the diet.

Feed at dusk to start. Wiggle a strip with tongs near the cave entrance and hold still. They like to size up the target and then strike. Juveniles eat small amounts daily; adults do well with 3-4 meals per week. They will overeat if you let them, so watch the belly line and keep portions moderate.

How they behave and who they get along with

Mostly a cave sitter by day, all business at feeding time. Not aggressive in the classic sense, but anything bite-sized is a snack. They will claim a hide and defend it with a quick rush.

• Best setup - species-only in a large coldwater tank.
• Possible tankmates - other large, calm, coolwater fishes that do not fit in their mouth and will not bully them. Think along the lines of robust temperate scorpionfish or big searobins if you have the room and experience.
• Not reef safe - crustaceans and small fish will vanish. Corals are also a mismatch with the temperature requirement.

Breeding tips

Realistically, this is not a home project. Royal codling are broadcast spawners with pelagic eggs and larvae that need huge volumes of clean, cool water and live plankton rearing. There is no reliable way to sex them visually. If you are dead set on trying, you would need a very large chilled system and seasonal temperature changes, but success stories in hobbyist tanks are not out there.

Common problems to watch for

• Overheating - above 18-19 C they get lethargic and go off food. Keep the chiller serviced.
• Low oxygen - first signs are rapid gilling and hanging near the surface. Add aeration and reduce temperature swings.
• Refusal to feed - often stress or too much light. Dim the tank, switch to squid or fresh shrimp, and feed at dusk with tongs.
• Capture damage - fish collected deep may arrive with barotrauma, popeye, or buoyancy oddities. Mild cases improve with time in dim, stable water.
• Internal parasites and flukes - most are wild-caught. Run praziquantel and metronidazole in QT and watch stool for worms.
• Skin abrasions - they have delicate skin. Use soft sand, stable rock, and avoid sharp decor. Treat secondary infections promptly.