A NSW Government website

Freshwater aquaculture

Silver perch

'Winter disease' or 'winter saprolegniosis' is a disease of silver perch which can be responsible for mass mortality events in grow-out ponds. The causative agent of winter disease is a water-borne fungus, Saprolegnia parasitica, and most outbreaks commence at water temperatures below 16°C. Detection can be difficult in characteristically turbid ponds, however heavily-infected fish often swim slowly near the surface of the water (Landos et al., 2007).

  • Winter disease in farmed silver perch (Bidyanus bidyanus) in NSW non-technical summary
  • Diagnosis, treatment & prevention of the diseases of the Silver Perch (PDF, 1730.88 KB)
  • Development of a Health Management Strategy of the Silver Perch Aquaculture Industry


NSW Department of Primary Industries (NSW DPI) has imposed tight restrictions on the culture of barramundi in NSW because of concern about the potential to introduce barramundi nervous necrosis virus (BNNV), also known as barramundi nodavirus, which could affect a number of species native to NSW.

The Protocol for Health Certification of Barramundi Fingerlings for aquaculture, prior to entry into NSW has a number of provisions to reduce the risk of introducing this disease into NSW and ensure farmers receive good quality, healthy stock. These include sterilisation of effluent, as well as a specific import protocol for the importation of barramundi fingerlings from out-of-state, which involves testing fingerlings for BNNV and other diseases.

Likewise, live barramundi cannot be imported live into NSW for other purposes, such as the ornamental fish or food trades, without a specific permit and health certification (see information on importation of live fish).


Poor hygiene is the most common cause of bacterial disease in trout hatcheries, where disease can spread rapidly if not identified and treated. Like other species, trout are more vulnerable to disease if stressed. Temperature stress (above 19°C) can be a problem in NSW, as well as overcrowding and low oxygen. Common parasites include Ichthyophthirius ('Ich' or 'whitespot') and Trichodina, both protozoans.

Trout are also affected by Epizootic Haematopoietic Necrosis (EHN) virus, which can be carried by introduced redfin perch and can have devastating impacts on some native species including threatened Macquarie perch.

Other species