rattail

Where they come from

Kumba dentoni is a deep-sea rattail (a grenadier) from the eastern Atlantic, showing up on muddy continental slopes off West Africa and nearby regions. Think 400-1,500+ meters down, cold, dark, and high pressure. Everything about their body plan screams slow, energy-saving cruising over soft bottoms.

Setting up their tank

If you are in an institutional setup and have access to the right gear, here is what has actually worked for deep-sea rattails in chilled systems.

• Temperature: 4-8 C, stable. You need a serious chiller and redundancy. Swings of more than 0.5 C in a day can stress them.
• Salinity: 34-35 ppt (1.025-1.026 specific gravity). Keep it steady.
• Lighting: ultra-dim. Red spectrum for viewing works well. Black out sides and back to cut reflections.
• Footprint: long, open runs with a soft-turn corner or rounded ends. They cruise more than they dart.
• Substrate: fine, dark sand or a sand-silt mix. Bare-bottom can work if you black it out and keep the room dark.
• Rocks/structure: low mounds or large PVC sections to break sightlines, but keep most of the floor open.
• Flow and oxygen: cool water holds oxygen, but they still want high dissolved O2 near saturation. Use strong aeration and a skimmer, with a broad, laminar current along the bottom.
• Filtration: oversize everything. Nitrification is slower at low temp. Big biofilter volume, high contact time, and a protein skimmer rated way above the tank size.
• Lid: tight and non-reflective. Spooks can lead to head strikes.

What to feed them

They are slow, methodical predators and scavengers. Forget flakes and pellets. Offer soft, marine-origin foods in small, frequent portions.

• Chopped marine fish, squid, and prawn.
• Mysis and enriched krill for smaller individuals.
• Gel-bound seafood mixes can help reduce mess at cold temps.

Feed with tongs or a target-feeding tube near the bottom so the food does not blow away. Two to three modest feeds per week is usually fine at 4-8 C. Pull leftovers within a few minutes; organics linger longer in cold water and will overwhelm your biofilter.

How they behave and who they get along with

Expect a calm, cruising fish that holds a gentle angle over the bottom and investigates slowly. They spook from sudden light or movement and will ping glass if startled.

• Tankmates: safest is none. If you must, only other large, very calm, deep-cold species collected in the same way. No active swimmers or bright, diurnal fish.
• Territory: they do not stake out tight territories, but they need uninterrupted space to move.
• Activity: crepuscular to nocturnal under dim light. Daytime, they often hold in open water just off the bottom.

Breeding tips

There are no credible captive breeding reports for Kumba dentoni. Macrourids are deep-sea broadcast spawners with pelagic eggs and larvae at depths and temperatures we cannot replicate outside specialized research facilities. Treat all specimens as wild-caught and non-breedable in captivity.

Common problems to watch for

• Decompression injury: gas bubbles under skin, exophthalmia, swim bladder issues. Prevention is the only fix; most cases are fatal.
• Thermal stress: pacing, rapid gilling, loss of equilibrium if temps creep above 10 C.
• Low oxygen: surface gulping or hanging in high-flow zones. Increase aeration and flow immediately.
• Head and lateral line abrasions: from glass strikes during spooks. Dim the room, black out reflections, and use rounded corners or foam bump guards.
• Ammonia and nitrite at low temp: biofilters are sluggish in the cold. Pre-cycle at operating temperature with heavy seeding, and test often.
• Feeding refusal: too bright, too much flow, or food presented too high in the water column. Switch to target feeding near the bottom in dim light.