Expedition Sheds Light on Rare Deep-Sea Fish Species

Researchers from The University of Western Australia undertaking deepwater ocean trawls of the Peru-Chile trench off South America are believed to have discovered three new fish species.

The work is part of ongoing research into vision in deep-sea fishesby Winthrop Professor Shaun Collin of UWA’s Oceans Institute and the School of Animal Biology, who was recently appointed to the Western Australian Technology and Industry Advisory Council,and his UWA colleagues Carolyn Kerr and PhD student Fanny de Busserolles.

The main purpose of the expedition was to study mesopelagic fish (midwater fish that live at depths of more than 100 metres), and how they detect and use bioluminescence (self generated light) to survive at these depths.

Working with teams of scientists from the United Kingdom, the United States, Japan, Germany and other parts of Australia, 20 trawls were undertaken at depths ranging from 100 metres to 1700 metres.

The trawls used a special net – the Midwater Trawl Net (Tucker Trawl) – developed and constructed by the Harbor Branch Oceanographic Institute in Florida and the University of Queensland under the Australian Research Council’s Deep Australia research grant in which Professor Collin is a Chief Investigator.

“It is suspected that at least three new fish species may have been discovered but this awaits verification by the experts on board from the Australian and Victorian museums,” Professor Collin said.

Professor Collin and Ms de Busserolles are particularly interested in how lanternfishes (or myctophids) travel big distances vertically each day from the relatively stable – but lightless – conditions at 1000 metres below the surface, to the upper water layers that are sunlight-dependent.  Typically, the pineal organ in the brain controls the diurnal (daytime) activity patterns of most animals, including humans.

“But how do these deep-sea fishes manage to migrate upwards nearly 1000 metres every night to feed in the nutrient rich upper water layers when there is little or no sunlight to signal night and day?” said Professor Collin.

“We’re interested in what the function of the pineal is in the deep sea and whether these image-forming eyes also play a role in setting their circadian (daily) rhythms.”

As depth increases, the selection pressures to retain image-forming eyes is large and although many species have risen to the challenge and possess large specialised eyes, others appear to have become degenerate or at least so small as to render them inefficient.

The seemingly degenerate eyes may take the form of small, aspheric globes or simply patches of light sensitive tissue over the head.  However, very little is known about the extent of visual loss experienced by these small eyes and patches of photo-receptive tissue and the environmental pressures (or signals) that initiate their loss of visual function.

“This research will potentially identify the barely essential neural elements that a simple visual system needs to operate,” Professor Collin said.

“It is the first time that such a wide array of different methods has been applied as an integrative approach for the investigation of sensory systems in deep-sea fish.”

The research is part of a large integrated study of the evolution and development of light detection in both shallow water and deep-sea organisms funded by UWA, the Australian Research Council, Deep Ocean Australia and the German Science Foundation.