It seems a bit unfair calling this a “rat-tail” fish when it clearly just has a thin, tapering tail. But naming its home after Hades certainly isn’t.

Get ready to gasp at some big numbers, because the 300-or so rat-tail species love big “0”s, and not just for their huge eyes or gaping mouths.

Leagues of their own

To start with, the rat-tail is the most abundant deep-sea fish, although sometimes it isn’t even that deep. Some, like the critically endangered bluntnose (Coryphaenoides rupestris), flicker about as shallow as 180m (590 ft) down in the “sunlight zone”. And on the other end of the scale, we have Coryphaenoides yaquinae, which has been found at staggering depths of 7,000m (22,965 ft) or more in the pitch-black “hadal zone” of the Mariana Trench.

If you don’t think permanent darkness at 1°C (33°F) is that terrible, wait until you hear the next big number. Atmospheric pressure is 1,100 times greater than at sea level, which according to researcher Mackenzie Gerringer, would feel like “a large elephant standing on your thumb”. You know, if you weren’t instantly and horribly crushed.

Speaking of extra weight, the rat-tail fish has a protective layer of heavy scales, hence its other moniker “grenadier”. Is this to fend off some horrifying, unseen deep-sea predator? Well, not as far as we know, because in many cases the rat-tail is at the top of the food chain.

But it looks so innocent!

Scavenger hunt

At the same depths as the abyssal spiderfish, there’s not a lot of light, warmth, or food going on, so it’s a case of munching tiny decapods, other small fish, and whatever bounty happens to float down from the surface. The higher up you go, the more predators, so light can be a double-edged sword. But the rat-tail can wield it just as well.

Down with the darkness

Like our firefly friends it has photophores – light-producing organs – but instead of mixing a cocktail of molecules and enzymes to make light, it uses bacteria, specifically Photobacterium phosphoreum. The javelinfish (Coelorinchus australis), for example, uses this to light up its belly and reduce its silhouette for any nasties swimming overhead. Even the biggest species, the giant rat-tail (Albatrossia pectoralis), has enemies, and this can land it in hot water for another reason.

The enemy of my enemy is…also my enemy. Dammit.

Charitably known as a “deep-sea trash fish”, the giant rat-tail was probably already annoyed at being a victim of bycatch for its enemy, the tastier sablefish, and almost always dies while being dredged up. While rat-tails can fling out as many as 100,000 eggs, bycatch may be a concern in future because they reproduce slowly. Why? Here comes another amazing number.

A rat-tail is for life, not just for Christmas

Some of the giant rat-tails caught were as old as 56. Not days, months, or in “fish years”. Human years. And they’re not even the oldest. That award goes to the Pacific rat-tail (Coryphaenoides acrolepis), which can reach an astounding 73. So it’s no surprise that some species don’t reach sexual maturity until 20. This, coupled with its apparently delicious taste, is one of the reasons the bluntnose is critically endangered. Well, they’re related to cod after all.

Most rat-tails are still at impressive numbers, but I quite like feeling my jaw drop at every little fact about them. Let’s hope it stays the only reason they leave our mouths hanging open.


Latin: Family name Macrouridae; there are up to 300 species

What? Deep-sea fish with a big head and large eyes tapering into a thin, rat-like tail

Where? Pretty much worldwide, and depending on species, from depths of 180m / 590ft to an incredible 7,000m / 22,965 ft!

How big? Usually 30-60cm /1-2 ft long, but the smallest is about 10cm / 3.9 inches long, the largest up to 1.4 m / 4.5 ft long.

Endangered? The bluntnose rat-tail is Critically Endangered due to over-fishing and a slow reproductive rate. A small handful are considered Data Deficient, otherwise the rat-tail is still considered one of the most abundant types of deep-sea fish.

Probable motto: All these awesome things about me, and you focus on my tail?

They sound cool! Do they need my help at all?

Despite the bluntnose’s critical situation, there don’t seem to be any specific conservation drives for rat-tails, but the Marine Fish Conservation Network, based in the US, is working towards sustainable fishing and helping rebuild fish populations. Conservation International also has an ocean drive (see what I did there?).

Just to prove I’m not fibbing:

Albatrossia pectoralis (Gilbert, 1892)”. No date.

Coelorinchus australis  (Richardson, 1839)”. No date.

Editors of Encyclopaedia Britannica. No date. “Grenadier“.

Fish, Rattail“. No date. The Marine Life Database.

Herring, P.J. et al. 2001. “Bioluminescence“. Encyclopaedia of Ocean Sciences.

Interactive Oceans. No date. “Bony fish“. University of Washington.

Jamieson, A.J. et al. 2008.”Liparid and macrourid fishes of the hadal zone: in situ observations of activity and feeding behaviourProceedings of the Royal Society B 276(1569).

Linley, Thomas D. et al. 2016. “Fishes of the hadal zone including new species, in situ observations and depth records of Liparidae“. Deep Sea Research Part I: Oceanographic Research Papers 114:99-110.

O’Connell, Sanijda. 2009. “What lurks in the depths of the ocean?The Telegraph.

Rattail Fish – Lepidorhynchus denticulatus“. 2016. The Sir Peter Blake Trust.

Rosen, Yereth. 2013. “New protections are on the way for deep-sea ‘trash fish’”. Anchorage Daily News.

Scripps Institution of Oceanography. 2006. “Deep-sea Fish Populations Boom Over The Last 15 Years, New Scripps Study Shows“. ScienceDaily.

Featured image credit: “Rattail fish – Submarine ride 2540 feet” by Mark Yokoyama