Gladstone Fish Health Investigation 2011 - 2012 - Western Basin ...

Figure 6. Eye condition observed in barramundi at each site sampled during Phase 1 of fish healthinvestigations, September 2011 – February 2012. Note, (n) refers to the total number of fish examined ateach site.Laboratory findings Phase 1The majority of the barramundi submitted for necropsy, including fish submitted prior to 16September 2011, showed eye lesions ranging in severity from inflammation to ruptured eyes.Severe skin lesions and abnormalities including generalised redness were also observed.Copepods (small crustaceans) were found on the gills of some barramundi in lowabundance. Copepods are not considered to be a serious pathogen at the observed level ofabundance.A number of barramundi showed a high number and intensity of melanomacrophage centres(MMCs) in organs (e.g. liver, spleen and kidney). An increase in MMCs is a commonhistopathological indicator of a range of factors or stressors including poor water quality,starvation, disease or ageing. The general function of MMCs is the focalisation, destruction,detoxification and recycling of internal and external materials. An increase in MMCs isgenerally likely to be the result of these catabolic physiological processes in the fish,commonly a negative nutritional balance (Agius & Roberts, 1981)There was no detectable sediment in the gills of the barramundi samples except for twosubmissions—see P11-76883 (Boyne River) and P11-76885 (Hamilton Point) in reports onwww.qld.gov.au/gladstoneharbourParasitic flatworm infection – Pathological examination of barramundi by BiosecurityQueensland identified a parasitic flatworm (Neobenedenia sp.) as the most likely causativeagent of the eye abnormality in the barramundi. Bacteria were excluded as the cause of thelesions. Flatworms can cause eye injuries by way of feeding and attachment over the surfaceof the cornea. In eyes that are cloudy, eroded, inflamed, swollen or where there is evidenceof haemorrhage, vision is likely to be reduced. In severe cases where the eye has beenruptured, this will cause blindness.The parasite moves over the surface area of the eye and the skin of the entire fish. A numberof barramundi showed hyperaemic (reddened) areas on the skin surface, which is consistentwith skin damage caused by the parasite feeding on mucous and skin cells on the skinsurface. This has been the first report of a significant outbreak of Neobenedenia sp. in wildbarramundi.Skin lesions and abnormalities – The causes of the deep, ulcerative lesions in barramundicollected in the early stages of the investigation from Gladstone Harbour were not able to bedetermined. Specific histopathology testing showed that Epizootic Ulcerative Syndrome(EUS), which is caused by a fungus, was not present in the samples collected fromGladstone Harbour, therefore EUS has been ruled out as the cause of these lesions. Onlytwo cases of EUS were found in testing: a barramundi taken in September 2011, which wascollected from Port Alma (at the mouth of the Fitzroy River), and in a whiting from theBundaberg region.Chemical residue testing – Barramundi samples were taken from five locations ─ PortAlma, Lake Awoonga and Fitzroy River (reference sites), and China Bay and Boyne River(Gladstone Harbour sites). Testing was conducted on the gill, liver and muscles of each ofthe fish or pooled fish samples.28