Comment »Posted on Saturday 10 January 2009 at 5:21 pm by Jacob Aron
In Biology

As a precursor to tomorrow’s weekly roundup, may I present three stories about our aquatic friends:

Live shark dissection

It’s not often you get to see the insides of a shark – and I’m not talking about being eaten! Earlier this week, the Auckland Museum in New Zealand held a live dissection of a great white shark. Marine scientists preformed the necropsy in front of 4,000 visitors to the museum, whilst a further 10,000 watched online.

During the dissection marine specialist Tom Trnski of the Auckland Museum and Clinton Duffy, a shark expert from the New Zealand Department of Conservation, discovered a fishing hook (line still attached!) inside the female shark’s stomach. No doubt that particular fisherman would be glad to have the shark be the one that got away!

Dr Trnski, speaking to Times Online, was “astounded” at the level of public interest:

“It’s quite interesting being a scientist and doing something that we consider fairly routine and not that exciting, to then catch the imagination of the people in New Zealand, Australia and internationally, we were all really astounded by the attention,” he said.

You can watch a short clip in the Times article linked above, or the whole dissection on the museum’s website. I must admit to not watching the whole thing – I’m a bit squeamish!

Fish have a three second memory? Not so fast

Fish are commonly believed to have three second memory, explaining why they will happily swim around in circles for hours on end. Not so, say scientists at the Israeli Technion Institute of Technology in Haifa, who discovered that they can remember for at least five months.

They spent a month training young fish to associate their feeding time with a certain sound, and then released them into the wild. When the sound was repeated five months later the fish returned, presumably expecting grub to be up.

The research could allow fish to be farmed in the wild, by training them whilst young and then summoning them at a later date to be caught for consumption.

“Four-eyes” uses a mirror to see

A fish which appears to have four eyes has been discovered to be the only vertebrate to use a mirror to produce an image. Known as Dolichopteryx longipes or the brownsnout spookfish, it actually only has two eyes, which are both split into two parts.

Spooky.
Spooky.

One part of the eye looks upwards and uses a lens to focus light from the sun, in much the same way as a human eye. Stranger though is the downward facing part of the eye, the mirrored surface of which collects light from the deep ocean and focuses it on the retina. It is thought that mirrors are more efficient than lenses in low-light, because a lens absorbs light as it passes through.

Professor Julian Partridge of the University of Bristol discovered the tiny mirrored plates, thought to be made of guanine crystals:

“In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes — how to make an image — using a mirror,”

“It’s an extraordinary animal. It is absolutely unique for a vertebrate. With mirrors it can make a very bright, high-contrast image.”


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