A Japanese team of scientists are now announcing that they are close to completing genome sequencing of the Bluefin tuna. Once they have reached this goal, their next project will be to use their knowledge to create a tuna breeding program for a new type of tuna specially designed for aquacultures.

The wild tuna populations have become severely depleted due to overfishing and the WWF has warned that the Atlantic Bluefin tuna will be eradicated within three years unless radical measures are taken to safeguard remaining specimens.

“We have already completed two computer sequencing runs and have around 60 per cent of the tuna genome,” says Dr. Kazumasa Ikuta, director of research at the Yokohama-based Fisheries Research Agency. “We expect to have the entire sequence in the next couple of months. We plan to use the sequence to establish a breeding programme for bluefin tuna as most aquaculture farmers presently use wild juveniles. We want to establish a complete aquaculture system that will produce fish that have good strength, are resistant to disease, grow quickly and taste delicious.”

The genome sequencing is the result of the collaborative efforts of scientists from Japan’s Fisheries Research Agency, Kyushu University, and The University of Tokyo.

Japanese eel (Anguilla japonica) larvae have amazing buoyancy compared to other oceanic plankton, and the reason may be a type of gelatinous goo contained within the body.

When researchers from the University of Tokyo measured the specific gravity of Japanese eel larvae, they found it to be as low as 1.019, rising to 1.043 – showing the larvae to be potentially lighter than seawater itself. (Sea water has an average specific gravity of 1.024.)

When they checked other marine creatures for comparison, such as juvenile jellyfish and the sea snail Hydromyles, their specific gravity turned out range from 1.020 to 1.425. Of 26 plankton creatures tested, the Japanese eel larva was the lightest.

The food consumed by Japanese eel larvae and many other planktons tend to be found in the greatest abundance really close to the water’s surface where there is plenty of light. The low specific gravity may therefore increase the survival rate of Japanese eels by making it easier for them to find a lot of things to eat.

So, why does the Japanese eel float so well? According the Japanese study, the answer may rest in gelatinous goo – or more specifically in a matrix of transparent gelatinous glycosamino-glycans. Controlled by osmoregulation through the chloride cells that cover the body of a Japanese eel larva, this marvellous adaptation makes it possible for the larva to stay close to the surface. Researchers have also suggested that it might help the larva to stay away from predators.

For more information, see the paper: Tsukamoto K, Yamada Y, Okamura A, Kaneko T, Tanaka H, Miller MJ, Horie N, Mikawa N, Utoh, T and S Tanaka (2009) – Positive buoyancy in eel leptocephali: an adaptation for life in the ocean surface layer. Marine Biology, vol. 156, no. 5. pp. 835-846.

New research has revealed that the tapetail, bignose and whalefish are in fact all the same fish.

For decades, three different names have been used for three very different looking underwater creatures: the Tapetail, the Bignose and the Whalefish. A team of seven scientists*, including Smithsonian curator Dr Dave Johnson, has now discovered that these three fishes are in fact part of the same family.

After studying the body structures of the tapetails (Mirapinnidae), bignose fish (Megalomycteridae) and whalefish (Cetomimidae) and taking advantage of modern DNA-analysis, the team realized that the three are actually the larvae, male and female, respectively, of a single fish family – Cetomimidae (also known as Flabby whalefish).

“This is an incredibly significant and exciting finding,” says Johnson. “For decades scientists have wondered why all tapetails were sexually immature, all bignose fishes were males and all whalefishes were females and had no known larval stages. The answer to part of that question was right under our noses all along—the specimens of tapetails and bignose fishes that were used to describe their original families included transitional forms—we just needed to study them more carefully.”

If you wish to find out more, the article “Deep-sea mystery solved: astonishing larval transformations and extreme sexual dimorphism unite three fish families” has been published in the journal Biology Letters by the Royal Society, London.

http://publishing.royalsociety.org/

http://journals.royalsociety.org/content/g06648352k5m1562/

* The seven scientists behind the discovery are:

G.David Johnson, Division of Fishes, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA

John R. Paxton, Ichthyology, Australian Museum, Sydney, New South Wales 2010, Australia

Tracey T. Sutton, Virginia Institute of Marine Science, Gloucester Point, VA 23062, USA

Takashi P. Satoh, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Tetsuya Sado, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

Mutsumi Nishida, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Masaki Miya, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

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.