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

ConclusionsIn 2011, a wide range of fish species in Gladstone were reported with health issuessupporting the hypothesis that the Gladstone Harbour ecosystem as a whole was understress. Barramundi provided the clearest and most consistent evidence for the cause of illhealth. In the other species, there appeared to be a range of observed symptoms. Anecdotalreports were received of increased levels of rust spot disease in mud crabs, firstcharacterised by Andersen and Norton (2001).An investigation began in September 2011 to determine the cause of the reported issues andspecifically to address public concern regarding the potential impact of industrial activityincluding dredging in Gladstone Harbour. The investigation, conducted by DAFF, was part ofa whole-of-government response.BarramundiIn September 2011, an external parasitic fluke Neobenedenia sp, was identified inbarramundi from the Gladstone Harbour. Neobenedenia was identified as the cause of theobserved eye problems and contributed to a number of the observed skin conditions inbarramundi.This parasite has previously been found in Queensland waters in the Hinchinbrook Channelbetween Hinchinbrook Island and mainland Queensland where barramundi are in highdensities (Deveney, et al, 2001), and had resulted in the loss of approximately 200 000cultured fish.An additional factor was the significant number of barramundi (estimated 30 000) washed outof the Awoonga Dam in the flooding during 2010/11. Many of these fish would have receivedphysical damage as a result of being washed over the spillway. This damage was reportedby recreational fishes as physical damage and was documented in necropsies of barramundiundertaken by a veterinarian with specialist skills in fish and aquatic animals in 2012 after asecond overtopping of Awoonga Dam. The fish showed damage to the jaw and head andusually presented with unilateral injuries to scales that appeared like a grazing along thebody.In the winter of 2011, the population of barramundi in the Boyne River was under extremestress. The densities of these large predatory barramundi in the Boyne River were at higherlevels than the system could naturally sustain, resulting in fish in poor condition and lowergrowth rates (Sawynok, et al, 2013). Their immune systems were further stressed by lowwinter water temperatures, resulting in an environment where the natural population of theparasite Neobenedenia could rapidly proliferate, and in turn resulting in observed eyeproblems and increases in fish exhibiting skin conditions (e.g. redness, loss of individualscales).As the water temperature increased, and the densities of barramundi were reduced byfishing (130 t of barra were caught by commercial fishers in the third quarter of 2011), theremaining barramundi became healthier. In 2012 and in 2013, other than barramundishowing relatively minor physical damage, no significant health issues have been reportedfor barramundi caught in the Gladstone region.These results are consistent with flooding and the significant number of barramundi beingwashed into the Boyne River. If the cause of the fish ill health continued beyond 2011, thehealth of the fish would not be improving and Neobenedenia infections would have beenseen in September 2012.74