Northern ronquil

Where they come from

Northern ronquils are cool-water rock and kelp line fish from the North Pacific, showing up from Alaska down the West Coast into California. You usually find them tucked into crevices on rocky reefs or hovering just off the bottom over sand-and-rubble patches. They are ambush hunters with quick dart bursts, not open-water cruisers.

Setting up their tank

Give them a low, wide tank with rockwork they can claim. A 40 breeder is the bare minimum for a single adult, but 55-75 gallons makes life easier and keeps temps steadier. Build a rocky maze with tight caves and some open sand in front so they can perch and pounce. Use a tight lid; they do jump when spooked.

• Temperature: 48-58 F (9-14 C) with a reliable chiller
• Salinity: 1.024-1.026
• pH: 8.0-8.3; high oxygen, strong surface agitation
• Flow: moderate with some brisk areas around the rockwork
• Lighting: dim to moderate; no need for reef-level brightness

Filtration needs to be oversized. Cold water holds oxygen well, but meaty foods foul the water. A big skimmer, generous biomedia, and frequent partial water changes keep things stable. Pre-chill your change water so you do not shock them. I like mixed-grain aragonite sand so they can brace themselves without scraping up their bellies.

What to feed them

They eat small crustaceans and little fishes in the wild. In a tank, start with moving foods to get their attention, then switch to frozen. Target feeding near their cave works way better than tossing food into the flow.

• Live or frozen mysid shrimp
• Frozen mysis, chopped prawn, chopped silversides/sand lance
• Small pieces of clam, squid, and krill (not as the only food)
• Live amphipods/shore shrimp to start stubborn eaters

Feed small portions once daily at first. After they settle, 4-5 modest feedings per week is fine; they put on weight quickly in cold water. Soak foods in a vitamin/omega supplement now and then. If they ignore frozen, wiggle it with tongs; once they realize it is food, they usually switch.

How they behave and who they get along with

Ronquils are perch-and-pounce fish. They claim a little territory and will do short dashes to grab food. Not bullies, but they will stand their ground, especially with similar-shaped bottom dwellers.

• Works with: similar-sized, calm temperate species that use different niches (e.g., midwater perch-like fish, small rockfish raised in captivity, bigger clingfish).
• Borderline: other benthic ambush predators of similar size (sculpins, gunnels) in small tanks. Space and sight breaks help.
• Avoid: very small fish, ornamental shrimp, small crabs. If it can fit in the ronquil's mouth, it is on the menu. Snails and urchins are typically safe.

Breeding tips

Spawning has been observed in the wild in spring. They lay adhesive eggs in a crevice, and a parent (often the male) guards the clutch. Getting that in a tank is rare but not impossible in a calm, mature system.

• Seasonal cues help: shorten day length and cool slightly over winter, then lengthen day and warm a couple degrees heading into spring.
• Provide multiple snug caves and rubble piles for nesting.
• Feed heavily with varied crustacean foods for conditioning.
• Larvae are planktonic and tiny. You would need live plankton cultures (rotifers, copepods) and a separate rearing setup.

Common problems to watch for

• Overheating: first sign is rapid breathing and hanging high in the water. Double-check chiller flow and room temps.
• Refusing prepared foods: kick-start with live mysids or amphipods, then transition to frozen using tongs.
• Bacterial nicks and fin frays from rockwork tussles: keep water ultra-clean; they respond well to pristine conditions.
• Internal worms and flukes (wild-caught): a round of praziquantel in quarantine helps a lot.
• Low oxygen at night: use strong surface agitation or an airstone, especially if the chiller restricts flow.
• Nutrient creep from heavy meaty feeding: big skimmer, frequent filter sock changes, and regular water changes.