Pakhorukov rockling

Where they come from

Pakhorukov rocklings are a coldwater, deep-living rockling from the North Pacific. Think steep, rocky slopes, dim light, and chilly water. They spend most of their time close to the bottom, slipping between cracks and caves.

Tank setup

Plan for a big, cold, quiet system with lots of cover. A 6 ft tank (180+ gallons) is a sensible starting point for an adult. They get long and snakelike, and cramped quarters make them pace and go off food.

• Temperature: 6-10 C (43-50 F). You need a serious chiller. For a 180-240 gal tank, you are looking at a 1/2 to 1 HP unit depending on your room temp.
• Salinity: 34-35 ppt. pH 8.0-8.3. Keep it steady.
• Oxygen: run strong aeration and surface agitation. Cold water holds more O2, but these fish are big oxygen hogs.
• Filtration: oversized skimmer, big biofiltration, and a mechanical stage you can rinse often. They are messy eaters.
• Flow: moderate along the bottom. Avoid blasting their caves directly.
• Substrate: fine sand or bare bottom. They like to rest on sand, but bare bottom is easier to keep clean.
• Aquascape: heavy rockwork with deep caves and tunnels. Use stacked rock plus large PVC sections hidden under rock for stability.
• Lighting: very dim. They are crepuscular. A red viewing light helps you watch without spooking them.
• Lid: tight-fitting with every gap covered. They will find the one hole you forgot.

Feeding

They are benthic predators. Getting them to eat steadily is the whole game. Start with movement and scent, then wean to prepared items.

• Starter foods: live or very fresh marine items like small shore crabs, grass shrimp, and ragworms/lugworms. Wiggly food flips the switch.
• Staples once feeding: strips of marine fish (hake, pollock, silversides), squid, clam, and shrimp. Offer with long tongs and make it wriggle near their face.
• Enrichment: soak in a marine vitamin mix a couple times a week.
• Avoid: freshwater feeders (goldfish/rosies) and oily fish as a staple (sardine/mackerel). You will end up with fatty liver and fouled water.
• Schedule: juveniles daily or every other day in small portions; adults 2-3 times per week. If they regurgitate later, you fed too much or too fast.
• Technique: present food at cave entrances with lights low. Once they learn the tongs mean dinner, feeding gets easy.

Behavior and tankmates

Shy at first, calm once settled. They spend daylight wedged in caves and cruise slowly at night. They are not aggressive for the sake of it, but a hungry rockling will treat bite-size fish and crustaceans as food.

• Tankmates to consider: other large, slow, coldwater fish that ignore the rockling and are too big to swallow. Think along the lines of sturdy sculpins or similar temperament, not fast pelagics.
• Tankmates to avoid: ornamental shrimp, small crabs, small fish, and boisterous swimmers that will outcompete them at feeding time.
• Multiple rocklings: possible in very large tanks with line-of-sight breaks and many caves, but expect territorial posturing if space is tight. Feed in separate spots.

Breeding

I have not seen a confirmed home spawning, and I do not know anyone who has. This species likely needs cold seasonal cues and space most hobby systems cannot provide. Sexing is not straightforward, and any larvae would be planktonic and extremely challenging to rear.

Common problems to watch for

• Refusal to feed: most common early issue. Try live marine invertebrates at dusk, reduce light, and reduce foot traffic near the tank.
• Barotrauma and handling damage from collection: look for buoyancy issues, popped eyes, or torn fins on arrival. If present, pass on the specimen.
• Temperature creep: chiller undersized or clogged. Put a temp probe where the fish actually live (near the bottom) and log daily.
• Low oxygen at night: heavy fish, closed lids, and skimmer offline can drop O2. Run an airstone in the display as backup.
• Skin abrasions: they wedge into rock. Keep rock stable, smooth sharp points, and maintain pristine water so scrapes do not infect.
• Internal parasites: wild-caught fish often carry them. Observe feces during QT and treat as needed under vet guidance.
• Overfeeding: they will take big mouthfuls and spit up later, nuking your water. Small, frequent, and targeted feedings are safer.