Memorable rearspined fin prickleback
Kasatkia memorabilis
The Memorable rearspined fin prickleback exhibits a slender body with distinct, elongated dorsal spines and mottled brown-green coloration.
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About the Memorable rearspined fin prickleback
Kasatkia memorabilis is a tiny, eel-shaped marine prickleback from the Sea of Japan area that spends its life down on the bottom in nearshore water. Its whole vibe is "hide in cracks and hug the rocks," so if you ever did keep one, you would treat it more like a coldwater tidepool fish than a tropical reef fish.
Quick Facts
Size
10 cm (3.9 in)
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
20 gallons
Lifespan
unknown
Origin
Northwest Pacific (Sea of Japan, Kuril Islands)
Diet
Carnivore - small meaty foods (tiny crustaceans/wormy foods), frozen and live
Water Parameters
6-14°C
8-8.4
8-12 dGH
Need a heater for this species?
This species needs 6-14°C in a 20 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Plan a coldwater setup, not a reef tank - these pricklebacks come from chilly North Pacific water, and they crash fast if you run them at tropical temps. I keep them around 50-60F with a chiller and strong oxygenation.
- Build the tank like a rocky tidepool: lots of tight crevices, caves, and overhangs, plus some macroalgae if you can. If it feels "too cluttered" to you, its probably finally enough cover for them to relax and eat.
- They are little escape artists that launch through gaps - lid needs to be tight, and cover overflow teeth and plumbing holes. Any opening bigger than a finger is basically an invitation.
- Feed meaty marine stuff and vary it: chopped shrimp, clam, mussel, squid, and quality frozen carnivore blends. Train them to take food from tongs near their hide so faster fish do not steal everything.
- Keep salinity steady around 1.024-1.026 and do not let ammonia or nitrite show up at all; they do way worse with swings than most hardy temperate fish. Nitrate staying low (ideally under ~20 ppm) helps keep them eating and not acting stressed.
- Tankmates: pick other temperate, non-bullying species that will not outcompete them at feeding time, and avoid aggressive rockfish/large wrasses and anything tiny they can gulp. If you want more than one prickleback, add them small together and give each its own bolt-hole or you will see constant jawing.
- Watch for fin damage and mouth scrapes from squeezing into rockwork or from dominance spats - those spots can turn into nasty bacterial issues in warm or dirty water. Also keep an eye out for parasites on wild-caught fish; a quarantine in a separate coldwater tank saves a lot of heartbreak.
Compatibility
Good Tankmates
- Other small, chill coldwater rockfish zone types like gunnels and other pricklebacks - they mostly ignore each other if you have lots of cracks and caves to claim
- Peaceful sculpins (like a grunt sculpin or similar small sculpin) - same vibe, they hang on the bottom and are not out looking for trouble
- Small, non-pushy greenlings (like kelp greenling juveniles) - they cruise around while the prickleback sticks to cover, so they are not constantly in each other's face
- Sailfin or other temperate snails and smaller hermits - good clean-up crew, and the prickleback usually treats them like furniture as long as you keep it well fed
- Sea stars and urchins (temperate species) - generally fine, and they actually help the tank feel more 'natural' with lots of grazing and rockwork activity
- Peaceful, non-stinging anemones or hardy temperate macros (kelp-y algae, reds) - gives it cover and reduces the whole 'everyone is staring at me' stress thing
Avoid
- Bigger, boisterous predators like lingcod, big rockfish, cabezon - they see pricklebacks as a snack and will eventually make the math work
- Aggressive/nippy fish that constantly pick at crevice dwellers (some wrasses and meaner damselfish types) - they will harass it out of its holes and it will stop eating
- Anything tiny that can fit in its mouth at night (small gobies/blennies, very small shrimp) - it is peaceful, but it is still a stealthy little opportunist
Where they come from
Kasatkia memorabilis is a cold-water prickleback from the North Pacific. Think rocky shorelines, kelp, surge, and lots of crevices. They are built for hanging on in rough water and wedging into cracks, not cruising open sand.
If your system is set up like a typical warm reef, stop and rethink. This fish really belongs in a chilled temperate tank.
Setting up their tank
The whole game with this species is temperature, oxygen, and structure. Give them rockwork that looks like a messy jetty - tight holes, overhangs, and rubble pockets - and they will pick a home and actually show themselves more.
- Tank size: I would not bother under 30 gallons for one, and 50+ is nicer if you want calmer behavior and more stable temps
- Temperature: true temperate/cold marine range (aim cold and steady - spikes are what get you)
- Flow: moderate to strong, but create calmer pockets behind rock where they can rest
- Gas exchange: aggressive surface agitation, big skimmer, and/or airstone in the sump - cold fish hate low oxygen
- Rockwork: lots of narrow crevices, plus a couple of deeper bolt-holes they can disappear into
- Lid: tight. They can launch themselves when startled, especially on the first few nights
Do not keep them in a warm reef tank long term. Even if they eat and look fine for a while, warm water and low oxygen will catch up with them.
I like a dimmer tank for them. Bright reef lighting makes them act like they are always on edge. If you are running macroalgae/kelp-style lighting, add shaded zones with rock shelves so the fish can choose.
What to feed them
In my experience they are not picky once settled, but they can be stubborn for the first week. Start with meaty, smelly foods and feed near their hiding spot. Once they learn the routine, they will come out like a little sea dragon and take food confidently.
- Best starters: chopped shrimp, clam, mussel, squid, and enriched frozen mysis
- Good staples: quality marine pellets (softening them first can help), frozen blends with varied seafood
- Treats: live blackworms (rinsed well) or live ghost shrimp can kickstart a shy new arrival
- Feeding rhythm: small portions 4-6 days a week; skip a day here and there so they stay interested
Use feeding tongs and place the food a few inches from their crevice at first. After a couple of sessions, they usually connect you with dinner and stop acting spooky.
Watch their belly line. A healthy prickleback looks solid and slightly rounded behind the head, not pinched. If it is not putting on weight after two weeks, something is off (usually temperature stress, bullying, or too much light/traffic).
How they behave and who they get along with
They are perch-and-pounce fish. Most of the day they sit in a crack with just the head showing, then they zip out for food and go right back. They are tougher than they look, but they do not appreciate being constantly harassed.
- Temperament: generally bold once settled, but territorial around their chosen crevice
- Tankmates to consider: other temperate, non-bullying fish that do not compete for the same holes
- Tankmates to avoid: aggressive rock-pickers, fast feed hogs, and anything that will nip or pry them out of cover
- Inverts: depends on the individual, but assume small shrimp/crabs can become snacks
Give each fish its own hiding options. If two fish want the same crack, one will lose, and the loser will stop eating.
They can do fine solo, and honestly that is how I would recommend keeping them unless you are very confident with temperate stocking and have a lot of rock. In a crowded tank they get jumpy and you will see more injuries from panicked dashes into rock.
Breeding tips
Breeding pricklebacks in home aquariums is not something you see often, mostly because you need a compatible pair, a stable temperate system, and time. They are crevice spawners, so if it happens, it will be in a tight cave you cannot easily see into.
- Set the stage with lots of narrow caves and a few deeper tubes/rocks with dead-end chambers
- Feed heavy on varied meaty foods for conditioning, but keep nutrients under control with export
- Keep the tank calm - minimal rearranging, minimal chasing tankmates, and stable temperature
- If you ever see guarding behavior at a hole, stop putting hands/tools near that spot
If you did get eggs/larvae, raising them would be a whole separate project (live plankton foods, dedicated rearing setup). Most hobbyists are happy just seeing courtship and guarding behavior.
Common problems to watch for
Most issues with this species trace back to the fish being kept like a tropical reef fish. Cold-water fish can look fine right up until they do not, so you have to read the early signs.
- Heat stress: rapid breathing, hanging in high-flow areas, refusing food, acting frantic under lights
- Low oxygen: gilling hard at night or early morning, camping at the surface, sudden lethargy
- Shipping damage: scraped noses and mouths from pushing into bags/rock - they wedge themselves into anything
- Not eating: common first week; usually fixed by dim light, quiet tank, and offering clam/mussel
- Jumping: most often right after introduction or after being chased
- External parasites: flashing, excess slime, frayed fins - quarantine pays off with wild-caught temperate fish
If you see rapid breathing plus hiding in the open (no longer tucked into a crevice), treat it like an emergency. Check temperature first, then oxygen and ammonia. This species goes downhill fast if the basics are off.
One last practical thing: keep your rock stable. These fish wedge hard, and if you have a teetering stack, they will eventually find the weak spot. I epoxy or pin the main pieces and then add rubble around them so the whole structure feels locked in.
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