The primary precursor to disease in wild populations is usually stress from physical or chemical factors such as lowered water temperature, rapid changes in salinity, chronic pollution or crowded conditions. In many cases the disease-causing parasites, viruses, microbes or fungi are present in low levels even in healthy populations, with environmental conditions or other stressors reducing the resistance to disease and making the fish susceptible to infection.

Australia is relatively free of many of the major fish diseases present overseas. Introduction of new diseases, for example via imported products, can lead to increased deaths in native species which have no exposure and hence little resistance to the new disease. For example, the much publicised death of millions of pilchards in coastal waters of southern Australia in May 1995 is thought to have been due to a newly introduced viral disease (see Whittington 1996 (www.int-res.com)).

Diseases in Abalone (Haliotis rubra)

Perkinsus (Perkinsus marinus, Perkinsus olseni)

From the early 1990s through to the early 2000s the protozoal parasite Perkinsus had a devastating effect on abalone stocks around Port Stephens, Terrigal, Sydney and Kiama. In some areas, it caused abalone numbers to drop to just 5% of their former populations. The major risk to abalone occurs when the infected animals are stressed or if the parasite is introduced into a new population. The Perkinsus parasite is not harmful to people. Since the mid 2000s there have been no reports of mortalities from Perkinsus and there has been some signs of recovery of abalone stocks especially in the southern part of the affected area and some areas have been reopened to limited commercial and recreational fishing.

To allow abalone stocks to further recover following outbreaks of Perkinsus, all recreational and commercial fishing for abalone remains banned between Port Stephens and Botany Bay until 30 June 2012. The closure starts at Tomaree Headland and is not inclusive of waters inside Port Stephens (eg. Shoal Bay is not closed but Fingal Bay is closed to abalone collecting). The closure then extends south to the southern entrance of Botany Bay and includes the waters of Botany Bay.  Limited commercial fishing is allowed between Botany Bay and Wreck Bay with recreational fishing also allowed on weekends and adjacent NSW public holidays. For more information see link below to formal closure notice. Heavy penalties apply for closure breaches. 

DPI will continue to monitor abalone stocks in the Port Stephens to Botany Bay area.

• Abalone closure – Port Stephens to Jervis Bay (37 kb, ) 
• Summary of Proceedings from the Perkinsus Workshop held at the Cronulla Fisheries Centre on 3 September 2003
• See Legislation – declared diseases and quarantine orders for details of the abalone fishing closure.

Abalone viral ganglioneuritis

Abalone viral ganglioneuritis (AVG) causes ganglioneuritis (inflammation of the nervous tissue, resulting in curling and paralysis of the foot and swelling of the mouth). AVG has caused devastating losses to the Victorian abalone industry and has also been detected in seafood processing facilities in Tasmania, most recently in November 2011. It has not been detected from any other State, though there is potential for it to spread.

• Abalone viral ganglioneuritis (AVG). The NSW Government has implemented a temporary suspension on imports of live abalone from Tasmania.
• Closure to help keep abalone disease out of NSW
• Information on AVG – Victorian Department of Primary Industries (www.dpi.vic.gov.au)
• Information on AVG – DPIPWE Tasmania (www.dpiw.tas.gov.au)
  

Diseases in Wild Fish

Red Spot Disease

Epizootic ulcerative syndrome (EUS) or 'red spot disease' is a disease that can affect many species of fish. Red spot disease is known to be endemic in a number of waterways in NSW. In 2008 reports of red spot disease were confirmed in the Darling River. In 2009 it was confirmed in Port Stephens and the Clarence River and reported from the Richmond, Manning, Macleay and Tweed Rivers. In 2011 it reported and confirmed in fish from Fullerton Cove in the Hunter River and Salt Creek on the Murray River.

2008 was a particularly bad year for EUS, with reports of ulcerated fish and confirmation of this disease in a number of estuaries including the Manning River in February, the Wisemans Ferry area of Hawkesbury River in March and in Myall Lakes in September. EUS was also reported from a number of mid-north coast NSW estuaries in 2008, including Macleay, Richmond, Clarence, Hastings and Wallamba Rivers. In addition to these coastal reports of red spot disease, fish sampled between Bourke and Brewarrina in the Darling River during May 2008 were also diagnosed with EUS.

EUS is caused by a fungus (Aphanomyces invadans) and shows as red lesions (sores) or deep ulcers Secondary bacterial infections are often also associated with red spot disease.

EUS is reasonably common in NSW coastal catchments and has been previously reported in many freshwater catchments and estuaries throughout Australia, including NSW, Queensland, Western Australia and the Northern Territory. Many fish species are known to be susceptible to the disease including bony bream, silver scat, sole, bream, mullet, whiting, dusky flathead, silver trevally, eels and catfish.

Previous outbreaks of EUS have been associated with acid water run-off, particularly after heavy rain following a prolonged a dry spell, as well as other factors such as prolonged cold temperatures, crowding, and conditions associated with drought.

Healthy fish with no sign of EUS can still be caught and consumed by recreational fishers and caught and sold by licensed commercial fishers.

SEVERELY ulcerated fish should:

• Not be eaten (on advice from the NSW Food Authority)
• Not be returned to the river or waterway
• Be euthanased by quickly removing the head (following immersion in ice slurry if possible)
• Be disposed of in landfill away from any waterway.

EUS Stages

Beginning of infection. Red spot lesions: Small area of reddening over single scale a ‘red-spot' (circled in red).

Moderately ulcerated fish: ‘Red-spot’ expands and deepens

Severely ulcerated fish: ulceration with loss of scales and skin, exposing underlying muscle.

DPI monitors the occurrence EUS, as well as other aquatic diseases. Please report any suspected occurrences of EUS to DPI by phone on 02 4916 3877 (recorded 24 hour service) or by e-mail to aquatic.pests@industry.nsw.gov.au

Bony Bream from the Darling River at Bourke showing EUS lesion (picture R. Reece).