A UK-Japan team equipped with remote-operated landers has now managed to film a shoal of Pseudoliparis amblystomopsis fish at a depth of 7.7 km (4.8 mi) in the Japan Trench, where the oceanic Pacific plate subducts beneath the continental Eurasian plate.

The deepest record for any fish – over 8 km / 5 mi – is held by the species Abyssobrotula galatheae, but this fish was never filmed or observed while it was alive; it was dredged from the bottom of the Puerto Rico Trench and already dead when it reached the surface.

The Pseudoliparis amblystomopsis film shows the fish darting around in the dark, scooping up shrimps. The shoal consists of no less than 17 specimens, with the largest ones being around 30 cm (12 in) in length.

It was an honour to see these fish“, says Dr Alan Jamieson, Research Fellow at the University of Aberdeen, Scotland. “No-one has ever seen fish alive at these depths before – you just never know what you are going to see when you get down there.

The filming took place as a part of the Hadeep project; a collaboration between the Oceanlab at the University of Aberdeen and the Ocean Research Institute at the University of Tokyo. The aim of the project, which is funded by the Nippon Foundation and the Natural Environment Research Council, is to find out more about life in the very deepest parts of the world’s oceans.

Just like the unfortunate Abyssobrotula galatheae, deep sea fishes tend to be in a sad state when researchers examine them at the surface and this is one of the reasons why a film is such great news for anyone interested in learning more about what’s going on at these vast depts.

According to Professor Monty Priede, also from the University of Aberdeen, the team was surprised by the fish’s behaviour. “We certainly thought, deep down, fish would be relatively inactive, saving energy as much as possible, and so on,” says Priede. “But when you see the video, the fish are rushing around, feeding accurately, snapping at prey coming past.

Oceanographers normally divide the deep sea into three different depth zones:

  • The Bathyal, which is located between 1,000 and 3,000 m (3,000 and 10,000 ft)
  • The Abyss, which is located between 3,000 and 6,000 m (10,000 and 20,000 ft)
  • The Hadal, which is located between 6,000 and 11,000 m (20,000 and 36,000 ft)

The Hadeep project has been looking at the creatures inhabiting the Hadal zone, which consists of comparatively narrow trenches in the wide abyss. In this environment there is no light and the pressure is immense. The food supply is also very limited, since photosynthesising organisms can not survive and most other creatures stay away as well. The animals living in the Hadal zone must therefore rely on food sinking down to them from more fruitful waters above.

In order to cope with pressure, Hadal dwellers display numerous physiological modifications, primarily at the molecular level. They have also developed various ways of dealing with the constant night and Pseudoliparis amblystomopsis is for instance equipped with vibration receptors on its snout which comes in handy when the fish navigates through the darkness and searches for food.

Dr Alan Jamieson now hopes that the Japan-UK team will find more fish during their next expedition down into the Haldal zone, which is planned to take place in March 2009 and aims to venture as far down as 9,000 m (30,000 ft).”Nobody has really been able to look at these depths before – I think we will see some fish living much deeper,” says Jamieson, whose deep-sea blog from the expedition can be found at Planet Earth Online.

You can also read more about this story over at deep sea news, a great blog if you want to keep up to date on deep sea discoveries.