Stripefin ronquil
Rathbunella hypoplecta
The Stripefin ronquil exhibits a slender, elongated body with striking silver stripes and a distinctive long dorsal fin.
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About the Stripefin ronquil
This is a little bottom-hugging California coast fish that hangs around rocky and sandy spots and spends a lot of time tucked into structure. It eats small invertebrates and the male actually guards the eggs, which is pretty cool if you are into fish with real parenting behavior.
Also known as
Quick Facts
Size
24.5 cm TL
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
40 gallons
Lifespan
unknown
Origin
Eastern Pacific (California to northern Baja California)
Diet
Carnivore - small invertebrates; in captivity would be meaty frozen foods
Water Parameters
12-18°C
8-8.4
8-12 dGH
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This species needs 12-18°C in a 40 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Plan for a coldwater marine setup, not a tropical reef tank - aim for 50-58F (10-14C) with a chiller and steady temps, because warm swings wipe them out fast.
- Give it a rocky, kelp-forest-style scape: lots of crevices and shaded overhangs, moderate flow, and a tight lid since they can launch when spooked.
- Run the water like a clean temperate system: salinity 1.024-1.026, pH around 8.0-8.3, and keep nitrate under ~20 ppm; they get sulky and prone to skin issues in dirty water.
- Feed meaty small stuff 1-2 times a day - mysis, chopped clam, krill bits, enriched brine, and small pellets if you can wean them; target feed near their hide because they are not pushy at the dinner rush.
- Tankmates: other temperate, non-bully fish that do not outcompete them (small sculpins, other ronquils, mellow rockfish juveniles); skip aggressive wrasses, large rockfish, or anything that treats them like a snack.
- They are perch-and-dart ambush feeders, so do not stick them with hyperactive grazers that steal every bite; if it is not getting food, it will just fade over a few weeks.
- Watch for shipping stress and gill irritation - heavy breathing, hanging in flow, and refusing food usually means ammonia burn or too-warm water; have a cycled QT that matches cold temps and salinity before the fish arrives.
- Breeding in home tanks is basically a long shot; if you ever see courtship, expect eggs tucked into rock cracks and the parents not doing you any favors, so protect the site from cleaners and powerhead intakes.
Compatibility
Good Tankmates
- Other peaceful coldwater rockfish neighbors - small sculpins and clingfish types (as long as they are not the super territorial kind). Stripefin ronquils mostly mind their own business and just want a crack in the rocks to hang around.
- Peaceful schooling fish from the same kind of coldwater setups - small surfperches or other non-predatory midwater fish that are not pushy at feeding time. They do fine with calm, steady tank traffic around them.
- Chill bottom cruisers like small pricklebacks or gunnels (the mellow species). They share the rockwork without turning it into a turf war, especially if you have lots of caves and broken sight lines.
- Non-aggressive inverts - cleaner shrimp, hermits, snails, urchins. Most ronquils ignore them if the fish is well-fed, and the inverts help keep the tank tidy around the rockwork they like.
- Peaceful anemone and coral-safe type tank mates (if your coldwater system supports them) - basically anything that is calm, not a fin-nipper, and not competing for the same exact hidey-hole.
- Small, non-bitey goby-like fish (coldwater equivalents) that perch and scoot around. Similar vibe, no drama - just make sure everyone has their own little patch of rock.
Avoid
- Aggressive or super territorial rockwork hogs - big sculpins, mean rockfish, or anything that wants to claim the whole cave system. They will out-muscle a ronquil and keep it stressed and hiding.
- Anything predatory enough to see it as a snack - lingcod-type predators, big kelp greenling, larger cabezon, etc. If it can fit the ronquil in its mouth, it will eventually try.
- Nippy fish or hyperactive feeders that blitz the food - they do not usually attack the ronquil, but they will starve it out and keep it pinned in the rocks.
Where they come from
Stripefin ronquils (Rathbunella hypoplecta) are little cold-water porch sitters from the northeast Pacific - think California up into Baja, hanging around rocky reefs and kelp edges where there is surge, shade, and plenty of tiny critters to ambush. They are not a tropical reef fish, and that single fact is what makes or breaks most attempts with them.
If your system is built around 76-78F tropical reef temps, this is the wrong fish. They want cold, clean, oxygen-rich water.
Setting up their tank
Give them a chilled marine setup with lots of structure. In the wild they wedge themselves into rock cracks and sit tight, so a bare tank makes them feel exposed and they just go downhill.
- Tank size: I would not do one in less than 30 gallons, and 40+ is way easier for stability.
- Temperature: cold-water range. Aim roughly 52-60F (11-16C). Consistency matters more than chasing an exact number.
- Salinity: 1.023-1.026. Keep it steady.
- Flow and oxygen: moderate to strong flow plus aggressive surface agitation. They are used to surge and high O2.
- Aquascape: stacked rock with caves, overhangs, and tight crevices. Leave open sand patches so you can actually spot-feed.
- Lighting: they do not need bright light. Dimmer, bluer lighting tends to keep them calmer.
Plan for a real chiller and a controller. Fans and "cool room" tricks are fine for a while, then summer hits and you find out fast why people call this species expert-level.
Filtration-wise, think messy predator even though they are small. They eat meaty foods and spit bits. A good skimmer helps a lot, and I like running carbon to keep the water from getting that "seafood soup" smell. I also keep nitrate low with water changes rather than trying to out-tech it.
What to feed them
They are micro-predators. Mine did best once I stopped offering big chunks and switched to smaller, more frequent feeds. If they are new, live or moving food often flips the switch and gets them eating.
- Best staples: enriched mysis, chopped krill, finely chopped clam/scallop, small pieces of shrimp, quality marine carnivore pellets once they recognize them.
- Great "get them started" foods: live blackworms (rinse well), live amphipods/copepods, live enriched brine (as a bridge, not a staple).
- Feed style: target feed with a pipette or turkey baster so the food lands right in front of their hideout.
- Frequency: small meals 1-2x daily beats one big dump.
Soak frozen foods in a vitamin/HUFA supplement a couple times a week. Cold-water fish still benefit from enrichment, and it helps when they are picky at first.
Watch their body shape. A healthy ronquil looks sleek but not pinched behind the head. If you see that "hollow cheek" look, it is usually not getting enough food (or it is being outcompeted).
How they behave and who they get along with
They are shy, a bit cryptic, and they spend a lot of time parked in one spot, especially during the day. At feeding time they can be surprisingly bold, but they are not built to fight for food with pushy tankmates.
- Good tankmates: other cold-water, non-aggressive fish that will not harass or outcompete them. Think mellow sculpins, smaller rockfish species (carefully), clingfish, and other chill temperate species.
- Avoid: boisterous feeders, fin-nippers, anything that will perch on them or shove them out of caves.
- Also avoid: anything small enough to be swallowed. They are not huge, but they will take tiny fish and shrimp if it fits.
Mixing temperate and tropical species usually ends in disappointment for one side or the other. Pick a lane: temperate/cold-water community or a tropical reef. This fish wants the temperate lane.
They appreciate multiple bolt-holes. If you keep more than one, spread the caves around so a dominant one does not claim the only good crevice. Even then, I would only try a pair in a bigger tank with lots of rock.
Breeding tips
Breeding them in home aquariums is not common. In the wild, ronquils are demersal spawners (eggs laid on a surface) and the male often guards. The hard part in captivity is getting a settled pair and then raising tiny larvae in cold water with the right plankton.
- If you want to try: start with a larger, mature chilled system and a well-fed pair.
- Provide: flat rock faces and caves where eggs could be laid and guarded.
- Seasonal cue: many temperate fish respond to gradual temp and photoperiod changes. Slow changes over weeks, not sudden swings.
- Larvae: expect very small food needs (rotifers/copepod nauplii) and a separate rearing setup.
If your goal is "I want to breed something," there are easier temperate species. If your goal is "I want to keep ronquils well," focus on long-term stability and getting them eating aggressively.
Common problems to watch for
Most issues with Stripefin ronquils are husbandry-related: temperature swings, low oxygen, and starvation from competition or finicky feeding. They can look fine right up until they do not, so I treat any behavior change as a warning.
- Heat stress: rapid breathing, hanging in high-flow areas, lethargy. Fix the temp problem first, then worry about anything else.
- Low oxygen: similar signs to heat stress. Add surface agitation, clean pumps, and do not let the skimmer go offline for long.
- Not eating: the big one. If it is hiding constantly and ignoring food, try smaller foods, target feeding, and live "starter" foods.
- Parasites/wild-caught baggage: flashing, excess mucus, weight loss despite eating. Quarantine is your friend, but it has to be a chilled QT.
- Injury from rockwork: they wedge into tight spots. Make sure your rock is stable so it cannot shift and pin them.
Do not do warm freshwater-style treatments like raising temperature to fight ich. With this species, heat is the enemy and will make everything worse.
My rule with ronquils: if something is off, check temperature and oxygen first, then watch a full feeding session. If they are eating well and breathing normally, you are usually on the right track. If they are not, act fast and keep changes steady rather than swinging parameters around.
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