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

provided another environmental stress. Under these conditions, Neobenedenia populationswere able to multiply, resulting in the symptoms observed.The outbreak of Neobenedenia infection in Hinchinbrook cage culture resulted in the loss ofan estimated 200 000 fish. All sick, dying and dead fish were removed from the cages anddisposed of on land. Wild sick barramundi in Gladstone were not removed as would occur inan aquaculture operation, but remained in Gladstone waters. Although low numbers ofbarramundi were reported to have died in the second half of 2011, it is believed that most ofthe infected fish survived.Given the severity and high frequency of health conditions observed in barramundi inOctober 2011, the fish in Gladstone Harbour and adjacent waterways would have showedsigns of poor health for an extended period of time. This is what was observed for theremaining samples taken in 2011 by Fisheries Queensland. In 2012, Fisheries Queenslandobserved fish recovering from the loss of significant areas of scales (Figures 11 and 12).As the water temperature increased, the Neobenedenia infection resolved in the populationof barramundi in the Gladstone area. Barramundi from Gladstone Harbour and adjacentwaterways sampled by Fisheries Queensland after October 2011 and reported by Landos(2012) were not identified as being infected with Neobenedenia.Although more barramundi entered the Boyne after the Awoonga Dam spillway overtoppedagain in late January to early April 2012, it is thought that the number of barramundi that mayhave entered the system was less than during the flooding event of 2010-2011.Neobenedenia are not expected to cause further issues in wild barramundi in the area undernormal environmental conditions.Laboratory findings Phase 2NecropsyNecropsy examination of barramundi in both trips one and two found a significant associationbetween field allocated disease status and liver abnormalities (P < 0.05) (Appendix B).Those fish that were allocated as diseased in the field (based on externally visible signs)were almost four times more likely to have liver form abnormalities than externally normalfish. It is not clear from this data whether the liver abnormalities are a consequence of theskin trauma or whether they are linked to another common factor, such as water quality ordiet.Field-based disease assessment was higher in fish from Gladstone than the reference sites.This was driven by the greater proportion of lesions in barramundi from the Boyne River inparticular. Interestingly, observed liver abnormalities in fish from the Boyne River were onlysignificantly higher than reference sites during Trip 2, despite significantly higher prevalenceof lesions in both trips. In Trip 2 only, skin condition, fin abnormalities and parasites weresignificantly higher in Gladstone barramundi than reference sites (P =