Japanese deepwater clingfish

Where they come from

Aspasma minima is one of those odd little Japanese clingfishes that lives deeper and colder than most of what we keep. Think rocky coastal slopes and crevices in Japan, where there is current, clean water, and not a lot of warm, sunny reef vibes. They are built to hang on - literally - and spend their time tucked into structure instead of cruising around the tank.

Setting up their tank

This species is expert-level mostly because of temperature and stability. They do best in a chilled marine setup. If you try to run them at standard reef temps, you are rolling the dice long-term, even if they look fine at first.

• Tank size: you can house one or a pair in a small tank, but I would not go under 15-20 gallons because micro swings (temp, salinity, oxygen) hit hard.
• Temperature: coldwater/chilled. Aim roughly 50-64 F (10-18 C) depending on what your collection source tolerates. Pick a target and keep it steady.
• Salinity: normal marine range (around 1.024-1.026) with very stable top-off.
• Flow: moderate, not blasting. You want oxygenation and gentle current over rock, plus calm pockets where they can park.
• Filtration: oversized for the tank. These fish are messy in a small-body way because you feed lots of small meaty foods.
• Lighting: dim to moderate. They do not need reef lighting and often act bolder with lower light.

Build the aquascape for a fish that wants ceilings and cracks. Lots of small caves, overhangs, and tight gaps between rock pieces. Flat stones and vertical faces are great because they like to attach and hover in place.

Use a lid. Clingfish are not classic jumpers, but deepwater fish can do weird panic darts, and you will hate losing one to a tiny gap. Also, keep intakes guarded - they can and will plaster themselves to a strainer.

What to feed them

In the wild they pick at tiny crustaceans and whatever drifts close. In a tank, you will be living the small-meaty-food lifestyle. They are not grazers and they are not going to convert to flakes like a clownfish.

• Best staples: enriched mysis (small pieces), finely chopped shrimp, calanus, copepods, amphipods if you can culture them.
• Good variety: finely chopped clam/scallop, roe, krill shaved small (sparingly), live foods during acclimation (live pods, small live shrimp).
• Avoid: big chunks they cannot mouth, and fatty "junk" feeding that clouds water in a cold system.

Target feeding helps a lot. Use a pipette or small baster and gently place food in the flow near their perch. Once they learn the routine, they will scoot a few inches and snap at passing bits. If you just broadcast, most of it ends up in rockwork and you end up chasing nutrients.

How they behave and who they get along with

They are quirky and pretty chill. Most of the time you will see a little face and fins, and then it is glued to a rock like a decorative lump. They do not "play" in the water column. They perch, creep, and ambush.

Tankmates are the biggest headache. You need fish that can handle the same cold temps and that will not outcompete them at feeding time.

• Good direction: small, calm coldwater species that ignore the bottom and are not food hogs.
• Risky: anything that pecks at benthic animals, anything aggressive, and anything that will steal every bite before the clingfish gets a chance.
• Also risky: big crabs and large predatory shrimp. A clingfish glued to a rock looks like an easy target in the wrong tank.

They can be kept singly. Pairs might work if you have enough hidey-holes and you introduce them thoughtfully, but do not assume two will automatically get along in a small footprint. I would rather see one well-fed fish than two that bicker and both fade.

Breeding tips

Breeding is not common in hobby tanks, mostly because deepwater clingfishes are finicky and people do not keep groups long-term in stable chilled setups. That said, clingfishes generally lay adhesive eggs in a protected spot, and the male often guards them in many species.

• If you want a shot: keep a bonded pair or small group in a mature cold system with lots of tight caves and flat undersides for egg placement.
• Feed heavy with varied meaty foods and pods for conditioning.
• Keep disturbance low around their favorite cave. They like privacy.

Common problems to watch for

Most issues I have seen (or helped others troubleshoot) come from three things: too warm, not eating enough, or oxygen problems.

• Temperature creep: summer room temps push the tank up and the fish slowly declines. Watch your actual daily highs, not just the controller setpoint.
• Starvation by stealth: fish hides more, gets thinner behind the head, and stops reacting to the baster. Usually caused by competition, stress, or food being too big.
• Low oxygen: coldwater systems can still have O2 issues if flow is poor or the surface is covered. Heavy feeding plus rockwork can create dead pockets.
• Shipping stress and decompression: deepwater fish can arrive rough even when they look "fine" in the bag. Go slow and keep lights low the first week.
• Intake and powerhead accidents: they stick to stuff. Use guards and avoid uncovered high-suction intakes.

If you are ever unsure whether it is eating, look for a slightly rounded belly after feeding and steady body weight over a couple weeks. These fish can go from "seems ok" to noticeably thin faster than you expect, especially if your tankmates are pigs.