Farming Barramundi

Husbandry & Health Status

Disease is generally not a problem providing good husbandry techniques are employed. Some diseases that have been encountered in Australia are described below (see also Makaira, 1999):

• In 1989, a small picorna-like virus infection of the brain and retina caused mortalities in 15-, 17- and 18- day-old larvae from a hatchery in North Queensland (Glazebrook et al., 1990). The pathogen responsible has since been identified as a piscine nodavirus and the disease has been named 'viral nervous necrosis' (VNN). The clinical signs of this disease include uncoordinated darting, corkscrew swimming, pale colouration, anorexia and wasting (Munday & Nakai, 1997). The disease can be controlled in hatcheries by not recycling culture water, chemical disinfection of influent water and larval tanks between batches, and reduction of larval stocking densities to not more than 15 larvae per litre (preferably less than 10/L) (Anonymous, 1995).
• Lymphocystis disease has been seen in marine cage cultured barramundi.
• Diseases caused by bacteria are the most frequently observed cause of mortalities in barramundi aquaculture.
• Due to lower stocking rates and a less intensive system, diseases common to tank reared fish have not been seen, to date, on extensively reared barramundi.
• Columnaris disease which causes fin and tail rot, is caused by long filamentous bacteria in the group Flexibacter and is mainly seen on fingerlings when sudden changes in water temperatures are experienced. Both freshwater and sea cage-reared barramundi are affected. Fin and tail rot is also associated with poor water quality, poor nutrition, overstocking and/or handling trauma. Reducing stocking densities and improvements in farm management are effective in preventing its re-occurrence (Anderson & Thomas, 1995).
• Bacterial infections of internal organs and deep skin ulcers following skin damage also occur in fresh water-reared barramundi. In fresh water, the disease is called Bacterial Haemorrhagic Septicaemia and has similar clinical symptoms to salt water vibriosis (Anderson & Thomas, 1995).
• White spot disease, the parasitic disease of skin and gills caused by the protozoan Cryptocaryon irritans, has been a major consideration in barramundi broodstock maintenance. White spot can be effectively controlled by salinity changes. If salinity changes are not possible (i.e. in freshwater culture), white spot can be treated by daily administration of copper sulphate at 0.5 parts per million (ppm) as a long term water bath (Schipp, 1996).
• The major predators of fish in ponds are birds, particularly cormorants. Control of predatory birds is difficult: various methods are discussed by Merrick & Lambert (1991). Dragonfly larvae prey on larval barramundi less than about 18 mm TL in fresh water ponds.