Robust assfish

Where they come from

Robust assfish (Bassozetus robustus) are deep-sea cusk-eels. Think slope and abyss edges, cold, dark water, and high pressure. They are not reef fish that wandered into the hobby - they are purpose-built for the deep.

Setting up their tank

If you are serious about this species, build the system around cold water and stability, not aesthetics. You are basically setting up a chilled marine predator tank with low light and a calm flow pattern.

• Temperature: cold. Aim roughly 39-50F (4-10C) depending on collection depth and what the specimen actually tolerates. A chiller is non-negotiable.
• Salinity: normal marine range (around 1.024-1.026), and keep it steady.
• Oxygen: pack it in. Cold water holds more O2, but these fish still appreciate big gas exchange and no stagnant corners.
• Lighting: dim. Give them a shaded zone and do not blast them with reef LEDs.
• Flow: gentle to moderate with dead spots eliminated. They are not built for surfing in a gyre.
• Aquascape: soft sand or fine rubble, plus caves and overhangs. Big PVC elbows hidden behind rock work also work great.
• Filtration: oversize it. These are meaty-food fish and the waste adds up fast.

Tank size depends on the individual and how it behaves, but do not cram it into a nano. Give it room to stretch out and turn without scraping its face on rock. More water volume also buys you stability when you are feeding heavy.

What to feed them

These are carnivores that expect animal-based foods. If you can get them eating reliably, you are halfway there. The other half is not fouling the water with leftovers.

• Good staples: thawed marine shrimp, chopped squid, strips of fish flesh from reputable sources, scallop, and quality frozen carnivore blends.
• Occasional treats: live or freshly killed marine crustaceans if you can source them safely (avoid introducing hitchhikers and pathogens).
• Feeding style: target feed with tongs or a feeding stick near their shelter. They often prefer food delivered to them rather than chasing it.
• Schedule: smaller meals 2-3 times a week usually beats daily dumping. Watch body condition and adjust.

If yours is shy, feed after lights down with minimal room traffic. I have also used a small dish on the sand for messy foods so you can pull leftovers easily.

How they behave and who they get along with

Expect a low-key, sit-and-wait predator vibe. A lot of the time they are tucked into a cave with just the head out, then they come alive when food hits the water.

• Temperament: generally not a brawler, but anything bite-sized is food.
• Tankmates: choose cold-water species with similar temp needs and a calm nature.
• Avoid: fast, nippy fish and anything that will harass it in its shelter. Also avoid small fish and shrimp you want to keep.
• Best setup: species tank or a quiet cold-water community with roomy hiding places.

Breeding tips

Breeding Bassozetus robustus in home aquaria is basically in the "not happening" category. Deep-sea fishes often have spawning triggers tied to pressure, seasonal cues, and huge ranges that we cannot recreate. If you ever see courtship behavior, log it and share it, because that would be genuinely useful info.

Common problems to watch for

• Heat stress: the big one. Even "cool" reef temps can be too warm long-term. Watch for heavy breathing, lethargy, and refusal to feed.
• Shipping/collection damage: deep-sea fish can come in rough. Look for jaw issues, buoyancy weirdness, abrasions, and cloudy eyes.
• Ammonia spikes from meaty feeding: easy to do in a new or undersized system. Test often, especially early on.
• Bacterial infections from injuries: these fish like to wedge into tight spots and can scrape themselves. Keep shelters smooth and openings roomy.
• Starvation by shyness: they can lose weight if tankmates steal food or if feeding happens in bright light.