Tubeshoulder

Where they come from

Tubeshoulders (Mentodus mesalirus) are one of those deepwater oddballs that look like they swam out of a nature documentary. They come from dim, offshore marine zones where the light is low, the water is stable, and food shows up in pulses.

That background matters, because a lot of the struggle in captivity is basically: bright tank, busy fish, and food that does not match what their instincts are tuned for.

Setting up their tank

Think calm, dim, and predictable. I have had the best luck keeping them in a species or quiet community tank with subdued lighting and lots of broken sight lines. They do not like feeling exposed.

Give them caves, overhangs, and vertical structure so they can hang back and watch. They are not a fish that wants to be out front all day under LEDs.

• Tank size: bigger is better, not because they are hyperactive, but because stability and space to avoid tankmates helps a lot (75+ gallons is a nice starting point).
• Lighting: keep it subdued, use shaded areas, and consider a longer ramp-up/ramp-down schedule.
• Flow: moderate and not blasting their favorite hideouts. Think gentle current they can sit in and out of.
• Rockwork: plenty of crevices and a few deeper caves. Leave open water lanes so food can drift past them.
• Filtration: strong biofiltration and aggressive skimming help, since you will likely feed meaty foods and want clean water.

What to feed them

Food is the whole game with tubeshoulders. They are not usually eager pellet pigs on day one. The ones I have kept did best with small, meaty items offered consistently, and I treated the first few weeks like a rehab program.

Start with foods that trigger a response: enriched live or freshly thawed items with movement in the flow. Once they are taking those confidently, you can transition toward frozen staples and maybe pellets, but do not rush it.

• Good starters: live blackworms (if you can source safely), enriched live brine, small live shrimp, or very fresh thawed mysis presented in current.
• Staples once settled: mysis, finely chopped shrimp, chopped clam, squid, krill pieces (not too much), and quality marine frozen blends.
• Enrichment: soak in a vitamin/HUFA supplement a few times a week. Deepwater fish often look better long-term with this.
• Feeding rhythm: small portions 2-4 times a day beats one big dump. They are built for frequent opportunities, not binges.
• Technique: use a feeding tube or turkey baster to place food near their zone without spooking them.

How they behave and who they get along with

They are more watcher than brawler. Mine spent a lot of time hovering near structure and darting out for food. They are not typically aggressive, but they are easily bullied or outcompeted.

Tankmate choice is mostly about avoiding stress and food competition. Fast, pushy eaters will make your tubeshoulder disappear into the rocks and slowly lose weight.

• Good tankmates: calm, non-nippy fish that do not race the tank at feeding time (think smaller, peaceful marine fish with similar temperament).
• Avoid: aggressive dottybacks, big wrasses, most triggers, boisterous tangs that dominate feeding, and anything that likes to pick at shy fish.
• Also avoid: fin nippers and fish that constantly cruise the rockwork looking for someone to bother.
• Grouping: I would not attempt multiples unless you have a large tank and a backup plan. Shy fish plus shipping stress plus hierarchy can go sideways fast.

Breeding tips

Breeding tubeshoulders in home aquariums is basically in the "nice dream" category. Like a lot of deepwater marine species, their spawning cues and larval requirements are not something most of us can replicate casually.

If you ever see courtship behavior, the best you can do is keep the environment stable, keep them well-fed, and avoid big changes. Document it, because observations on this kind of fish are genuinely useful.

Common problems to watch for

Most issues show up as slow declines rather than dramatic crashes. You want to get in the habit of watching body shape and feeding response, not just whether it is alive.

• Starvation/weight loss: sunken belly, pinched head profile, less interest in food. This is the big one.
• Shipping damage and delayed mortality: deepwater fish can arrive rough. Watch for heavy breathing, inability to hold position, and refusal to feed.
• Stress from light and traffic: constant hiding, darting, or staying plastered in one corner all day.
• Outcompeted at meals: it may eat at first, then stop once tankmates learn the routine.
• Parasites: flashing, excess mucus, or persistent rapid breathing. Quarantine is your friend if you can manage it for a sensitive fish.
• Bacterial issues from injuries: frayed fins, red marks, cloudy patches after a rough introduction or bullying.