Sharpnose sevengill shark

Where they come from

Sharpnose sevengills are deepwater cowsharks. They cruise continental slopes in temperate and tropical oceans, usually a few hundred meters down and sometimes past 1,000 m. Think cold, dim, and quiet. They come up higher in the water column at night to hunt small fish and squid, then drop back into the dark. That deepwater background is the main reason they are so tricky in captivity.

Setting up their tank

I kept mine in a chilled, round system and would not do it any other way. They pace and nose into corners if you give them rectangles. Round or oval is the move.

• Footprint and volume: minimum 25,000-30,000 L (6,500-8,000 gal) for a juvenile/subadult. 50,000 L+ is better. Aim for a 4-6 m diameter round tank, 1-1.5 m deep.
• Shape and surfaces: round tank or an oval raceway with rounded ends. No sharp corners. Smooth walls and a soft sand bottom (rounded aragonite). Skip live rock piles.
• Temperature: 8-14 C (46-57 F). They stress fast above 16 C. Use redundant titanium chillers and avoid swings bigger than 1 C per day.
• Oxygen and flow: high oxygen, gentle laminar current. Big protein skimmer, degassing, and an oxygen cone or fine diffusers. Keep microbubbles out of the display.
• Water quality: SG 1.025-1.026, pH 8.0-8.3, zero ammonia/nitrite, nitrate under ~25 mg/L. Stable beats perfect.
• Lighting: very dim. They hate bright white light. I use dim red for viewing at night.
• Lids and safety: tight cover and secure overflows. They are stronger than they look.

Filtration needs to be outsized. Think big wet-dry or moving bed biofilter, serious mechanical prefiltration, and a skimmer you would normally put on a full reef system. Plan for backup power, alarms, and spares for every pump that matters.

What to feed them

They are squid-and-fish specialists. Mine took food on a stick after a week of lights-down nights and patience.

• Staples: squid and cuttlefish strips, sand eels/lancefish, smelt, mackerel chunks. Rotate items.
• Supplements: soak foods in a marine vitamin mix (with B1/thiamine), plus HUFA (Selcon-type). Add iodine periodically to avoid goiter.
• Avoid: exclusively oily baitfish (thiaminase issues) and freshwater feeder fish. Cooked foods are a no.
• Frequency and amount: juveniles 2-3 small feeds per week; adults 1-2. Roughly 1-2% body weight per week, adjust to body condition.
• Technique: long acrylic feeding stick or tongs. Present just in front of the snout and let them take it cleanly. No tug-of-war.

How they behave and who they get along with

Sharpnose sevengills are mostly nocturnal cruisers. They are calm until they are not, and bright light or tight spaces make them frantic. Mine settled once the room stayed dim and the current was steady.

• Temperament: shy, light-sensitive, and very bump-prone. They nose walls if stressed.
• Tankmates: I do not recommend any. Anything small is food. Other large sharks or rays will stress them or get harassed.
• Activity: more active at night. Expect laps around the perimeter with pauses on the bottom if the current is mild.
• Human interaction: keep it minimal. They feed better and injure less with less traffic in the room.

Breeding tips

Realistically out of reach in private setups. They are aplacental viviparous (livebearers) with decent litter sizes, and they need massive space, seasonal cues, and multiple compatible adults. Even public aquariums rarely attempt it. If you ever ended up with a gravid female from the wild, dim light, very low stress, and excellent water are all you can offer.

Common problems to watch for

• Capture/decompression damage: exophthalmia, gas under the skin, odd buoyancy. Survival is poor if collected too fast from depth. Buy only from sources that decompress deepwater sharks properly.
• Rostrum abrasions: from glass-charging or hard decor. Round the layout, dim the room, and pad any intake grates.
• Heat stress: panting, frantic pacing, refusals to feed above 16 C. You need more chiller, not more air stones.
• Feeding strikes: often lighting or temperature related. Try squid at night with red light. Keep the room quiet for a week.
• Parasites and meds: copepods on gills/fins and flukes happen. Sharks are copper-sensitive; do not dose copper. Work with a vet for safe treatments.
• Ammonia and microbubbles: both burn gills. Keep NH3 near zero and stop bubbles from the sump reaching the display.
• Vitamin deficiencies: thiamine deficiency causes twitching or loss of coordination. Rotate diet and use vitamin soaks.
• Stray voltage: sharks feel it. Use GFCI and a titanium ground probe.