13 February 1998

University of Queensland researchers are tackling a novel project to minimise chronic stress in fish held in captivity.

The interdisciplinary project centres on one of Australia's highly-prized tropical eating fishes, the coral trout, in a bid to boost captive live coral trout exports to south-east Asia, the world's largest fish market.

'Shipboard survival of coral trout destined for export is reasonably high, but we would like to improve on this,' Dr Mike Bennett said. 'Loss of product from the high value live fish market is a major cause of reduced profitability in the fishery.'

Dr Bennett, of the Anatomical Sciences Department; his wife, Dr Sue Bennett of the Parasitology Department; and University of Queensland anatomist Dr Adrian Bradley are involved in the coral trout project with researchers at James Cook University of North Queensland and Curtin University of Technology, Western Australia.

Researchers are also studying the potential to develop a fledgling coral trout aquaculture industry in Australia.

Dr Mike Bennett said coral trout (Plectropomus leopardus) retailed at up to $100 per live product in the live export trade. The same-sized mature fish in Australia sold at about $30 each to the fillet trade.

'This price disparity explains why many fishing fleets are being re-equipped from catching and filleting operations to catching and holding fish alive in aquaria to be returned to the mother ship, then sent to markets such as Hong Kong and China,' he said.

'Estimates place the live export market for Australian coral trout at about $3.5 million per year, plus the cost of capital investment and air freight.'

Dr Bennett said researchers were building a reference framework by developing ways to measure stress.

For scientists, minimising stress in fish does not entail esoteric mood music, muted lights, transcendental meditation, or Feng Shui tank placement. The scientific way entails precise measurement.

Enter PhD student Tracey Turner. Over two years she is developing and performing 15 different assays to complete the picture on stress conditions in wild and captive fish.

Ms Turner and senior researchers are using coral trout from fishing vessels to quantify the stress fish are under and the effects of catching and keeping them aboard.

One possible stress factor being studied is the effect on the fish of abrupt changes in water temperature. Thermal changes may occur during capture, handling and transportation of fish from the reef to the shore.

They are also sampling in the field, from Great Barrier Reef locations including the waters adjoining the University of Queensland's Heron Island Research Station.

In the past two years, in addition to studying coral trout, Dr Mike Bennett and Ms Turner have examined more than 200 fish comprising 30 different species to provide a framework for interpreting the physiological data from coral trout.

Dr Bennett said little had been written about the physiology of tropical marine fishes. Most literature on stress in captive fish targeted northern hemisphere salmonids (such as salmon and trout).

Coral trout have quirky reproductive behaviour. They are monandric protogynous hermaphrodites - a ponderous name meaning they changed sex from females to males during the course of their lives, a common strategy in coral reef groupers.

As line fishing invariably targeted large animals, it could inadvertently reduce the number of males. It is not known what triggers sex changes in coral trout, but it could be induced by social behaviour during spawning, which occurs around the new moon between September and November.

Over the past six years, Dr Sue Bennett has studied the ectoparasites of coral trout. Her expertise will be valuable in any future plans to develop coral trout as a potential aquaculture species in Australia.

Dr Bennett said commercial culture could provide an alternative to fishing as continuing demand placed increase pressure on natural populations. The Queensland Department of Primary Industries has identified a number of coastal sites in the State suitable for reef fish aquaculture. However, to date, no one has been successful in hatching and rearing coral trout to maturity.

She is examining whether parasites could become a problem in an aquaculture situation.

'In the wild, fish carry relatively low numbers of parasites, but in a reticulating sea water system such as used in aquaculture, these could multiply to epidemic proportions,' she said.

'We are observing the effects of an increase in parasite numbers on captive fish, such as susceptibility to disease, formation of external lesions, damage to gills, or stress-induced disruption of osmoregulation ability.

'On the reef, these parasites may be kept under control by cleaner wrasse that feed on them. We would like to observe the effects of keeping cleaner wrasse in recirculating systems with the coral trout.'

The project has attracted three-year, $272,000 Fisheries Research and Development Corporation funding plus support from the Seaworld Research and Rescue Foundation Inc.

For further information, contact Dr Mike Bennett, telephone 07 3365 2705/07 3365 2944, email: m.bennett@mailbox.uq.edu.au, Dr Sue Bennett, telephone 07 3365 5756, email: s.bennett@mailbox.uq.edu.au or Dr Adrian Bradley, telephone 07 3365 3386, email: a.bradley@mailbox.uq.edu.au