It ’ s not a problem if you ’ re a deep water snailfish – the deepest fish in the ocean – and can lord it over the other hadal organisms , says Becky Hitchin
BECKYHITCHIN
Under pressure ?
It ’ s not a problem if you ’ re a deep water snailfish – the deepest fish in the ocean – and can lord it over the other hadal organisms , says Becky Hitchin
In the news recently was an article about the deepest fish ever caught on camera . This was a snailfish of a genus Pseudoliparis , seen swimming at 8,336m in a trench off Japan .
The first amazing thing about this is that it was a snailfish ! We have two snailfish in UK waters , Liparis liparis and Liparis montaguii . These are small tadpole-shaped fish , related to the lumpsucker and with a similar rounded sucker created from merging of the pelvic fins . They have scaleless skin which is loose , soft and slimy , hence the name sea snails or snailfish , I guess . Both species are found all round Britain and Ireland , though they are more common in Scotland and Wales , and a great sight seen curled up on kelp during safety stops in the Scottish sea lochs . These sea snails are usually found in shallow water , but can live down to 150m .
The second amazing thing is that snailfish have the widest depth range of any marine fish family , with the deepest examples known from seven of the world ’ s deepest ocean trenches . Unlike most other fish families , they thrive in waters 8,000 + metres deep , where they are seen clustered together in groups and feeding on tiny crustaceans using suction from their mouths to gulp in their prey .
In these hadal depths – hadal meaning nearly the bottom of the ocean – the depth zone from 6 to 11 km ( 3.7 to 6.8 miles ) below sea level – snailfish live free from predators and are themselves the top predator in an invertebrate dominated ecosystem . The pressure at these depths is unimaginable , with one rather colourful description being that it would be like an elephant standing on your thumb .
The third amazing thing is that snailfish seem to live as deep as fish can go . Below 8,400 metres there are no fish . It ’ s equally cold and dark above 8,400m as below 8,400m . Other creatures live below that magic depth , such as hadal amphipods that are known to exist over 10,000m . But not fish .
“ Snailfish have the widest depth range of any marine fish family "
So why is this ? Well , no one really knows but recently there was a suggestion that the problem is pressure . Yes , that very small change between an elephant standing on your thumb at 8,336m and an elephant with an added moustache standing on your thumb at 8,400m .
Pressure eventually crushes everything , even the proteins that are the building blocks of us all . There is an idea posed by researchers that seems to explain both how the snailfish live at depth , and also why they can ’ t go deeper than 8,400m . This is a molecule called trimethylamine oxide ( TMAO ). Trimetha-what ? I hear you cry . TMAO is a chemical that produces the smell
PHOTO : KIRSTY ANDREWS
A common snailfish Liparis liparis in shallow UK waters we associate with fish and it also helps cells function normally under pressure .
At high pressures , water molecules can force their way into little nooks and crannies of protein structures , disrupting them and therefore the functions of the proteins , but TMAO acts to protect the proteins from these water molecules all around them . This helps the snailfish to keep working normally , even at huge depths . However , as fish get deeper in the water column , they need more and more TMAO to keep cells working and researchers think that maybe 8,400m is the depth at which this helping function breaks down and thus is the limit for fish life as we know it .
So next time you see a tiny curled up lump on a kelp frond , wave hello and wonder if it ’ s dreaming big dreams of deep oceans , world records and breaking one of the last barriers known to fishkind . �
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