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

Phase 1 (August 2011–February 2012)Both commercial catch records as well as field observations confirmed there was anabnormally large population of barramundi in the Boyne River, with many of these fish beingexceptionally large. Recreational fishers indicated that the increased population ofbarramundi had been present since the flooding event in early 2011, with fish showing signsof damage but also recovery at first. During winter, when the water temperature was reportedto be as low as 18.1 o C, anecdotal evidence suggested deteriorating health in the barramundifrom the Boyne River including swollen, opaque eyes and ulcerated areas on the skin. Theinvestigation found that the fish were suffering from skin lesions and parasitic infestation(monogeneans on the body surface), conditions not previously documented from fish in awild environment, but are often recorded from fish held in heavily stocked aquaculturesystems.Other finfish species were observed with a range of generally mild skin conditions, includnglocalised skin inflammation, scale loss, skin erosion and redness. A fungal infection thatcauses skin lesions (Epizootic Ulcerative Syndrome (EUS) or ‘red-spot’ disease) wasidentified in two fish, both of which were outside of Gladstone Harbour. EUS was excludedas a potential cause of the lesions seen in Gladstone Harbour. No bacterial, parasitic orfungal pathogens were found that could explain the skin conditions.Phase 2 (April 2012–September 2012)BarramundiThe barramundi from the Boyne River caught in April 2012 were observed to have highprevalence of skin lesions thought to be caused by physical trauma, while fish captured inSeptember 2012 were observed with lesions that were healing. Infestations of themongenean parasite identified in Phase 1 were not observed during the Phase 2 structuredsampling.Based on weight-length relationships, mesentery fat assessment and livermelanomacrophage centres, barramundi sampled from Gladstone Harbour sites were in poornutritional condition compared with those from the reference sites. There were somebarramundi caught during sampling with relatively high levels of mesentery fat, indicatingexcessive intake of food. These fish tended to be found in the Boyne River and had lesionstypical of physical trauma caused by fish passing over a spillway, suggesting that theyprobably originated from Lake Awoonga.Chemical residue analysis of barramundi livers showed that fish collected from GladstoneHarbour had significantly higher concentrations of iron and cadmium during April 2012, andhigher arsenic and zinc levels than the reference sites in June/July 2012 (P ≤ 0.05).Comparison of concentrations of metals in barramundi livers with toxicological effects dataindicated that the concentrations in the barramundi liver were of no concern. In addition,there were no significant differences in these metal concentrations between fish with andwithout visible abnormalities.Other speciesSpecies other than barramundi were generally observed to be in good condition. Someabnormalities were observed in other species (e.g. shell lesions in mud crabs), howeveranalysis of the data indicated there was no evidence that these conditions were moreprevalent in fish or crustaceans from Gladstone Harbour when compared to those from thereference sites, or when compared with historical data.6