sciencetech-blog

comments

It is said that there are plenty more fish in the sea, but the popular maxim no longer holds true as fish are said to be on the road to extinction.

Reports in 2010 found that over-fishing and pollution is depleting the world's fish stocks, and now a team of scientists claims to have discovered how.

They state that 90 per cent of fish larvae are biologically doomed to die just days after hatching, because of the viscosity, or 'stickiness' of the water in which they are born.

On the verge of extinction? A team of scientists have found that 90 per cent of fish larvae (pictured) are biologically doomed to die just days after hatching because pollution makes the water they're born into viscous, and this slows them down when looking for food

And this stickiness is increased by pollution.

A scarcity of fish spells disaster for over a billion people around the world who are dependent on fish for their main source of protein.

The study, by Roi Holzman and Victor China of the Department of Zoology at Tel Aviv University, follows the 2010 report by the United Nations Environment Program.

The research, which was conducted at the Inter-University Institute for Marine Sciences in Eilat, and published in PNAS, suggests that 'hydrodynamic starvation,' or the physical inability to feed due to environmental incompatibility, is the reason so many fish larvae perish.

Nearly all fish species reproduce externally – releasing and abandoning their sperm and eggs into the water. The fertilised eggs hatch within a couple of days and the larvae must feed themselves.

They had previously fed on a yolk sac – a membrane joined to an embryo to provide early nourishment in the form of yolk – but once hatched, the vast majority die.

'We thought, something is going on during this period, in which the proportional number of larvae dying is greatest,' Dr Holzman said.

'Our goal was to pinpoint the mechanism causing them to die.

Disaster looming: A scarcity of fish spells disaster for over a billion people around the world who are dependent on fish for their main source of protein. A major report in 2010 blamed pollution levels and overfishing for the state of affairs. A fisherman casting his net in a lake in southern India is pictured

'We saw that even under the best controlled conditions, 70 per cent of fish larvae were dying within the two weeks known as the 'critical period,' when the larvae detach from the yolk sac and open their mouths to feed,' said Dr. Holzman.

Dr Holzman said that using their understanding of the mechanism that kills off fish larvae, could help 'find a solution to the looming fish crisis in the world'. A school of larval fish is pictured

Over two years, the researchers observed fish larvae at three significant points in their development - at eight, 13 and 23-days-old, or the beginning, middle, and end of that 'critical period'.

They found that the 'stickiness' or the viscosity of the surrounding ocean water was hampering the larvae's attempts to feed.

Polluted seawater is typically more viscous than clean water, and cooler water is slightly gloopier than warmer bodies of water.

'All that determines the larvae's feeding ability is viscosity - not age, not development – only their interaction with the surrounding water, Dr Holzman explained.

'Because the water molecules around you have weak electrical bonds, only a thin layer sticks to your skin - a mere millimetre thick. If you're a large organism, you hardly feel it.

'But if you're a three-millimetre-sized larva, dragging a millimetre of water across your body will prevent you from propelling forward to feed.

'So really, it's all about larval size and its ability to grow fast and escape the size where it feels the water as viscous fluid.'

The researchers found that in less viscous water, the larvae improved their feeding ability and in theory, this water would increase their survival rate.

'We conclude that hydrodynamic starvation is the reason for their dying,' Dr. Holzman said.

'Imagine eating soup with a fork – that's what it's like for these larvae. They're not developed enough at the critical point to adopt the constrained feeding strategy of adult-sized, better-developed fish.'

Dr Holzman said that by using their understanding of the mechanism that kills off the majority of the world's fish larvae, it could help 'find a solution to the looming fish crisis in the world.'

Armed with this knowledge of the larvae's biological flaw, the researchers are currently patenting a solution to maintain higher survival rates among fish larvae populations.