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

Mullet and other finfishUnlike barramundi, there did not appear to be a single symptom that characterised what wasobserved in other fish including mullet in Gladstone. Symptoms observed included loss ofscales, small red pin point wounds, red colouration of fins and body areas, and increasedlevels of parasites.One catch of queenfish in Phase 1 had a high frequency of fish with a high intensityinfestation of Lepeophtheirus spinifer (sea lice). From the total catch of queenfish, 41 of the46 fish had sea lice. This is the same catch of queenfish that was examined by Matt Landosand presented in his report.In Phase 1, in addition to this catch, a total of 56 queenfish were observed in Gladstone. Ofthese fish, two fish were reported as showing no external signs of ill health, but parasiteswere not recorded as either being present or absent. Of the remaining fish, 13 were recordedas having no external visual parasites. The only time that parasites were recorded onqueenfish in Phase 1 in Gladstone was this particular catch.In Phase 2, of the 23 queenfish examined from the Gladstone region, only eight hadectoparasites. For the reference sites, 26 out of the 36 queenfish from Bundaberg examinedhad ectoparasites, while two of the 12 queenfish from the Fitzroy River had parasites.It appears from the sampling conducted by Fisheries Queensland over an extended period oftime that the percentage of queenfish with parasites is not unusual (64% in Gladstonecompared with 58% in the reference sites). It appears that the school of queenfish caught onthe Spoil Ground was unusual in both the percentage of fish infected with parasites and thelevel of parasitism. If high frequency and high intensity of parasitism was a continuing issuein Gladstone, Phase 2 sampling would have continued to show high levels of ectoparasiteson queenfish. This did not occur.It appears that the ecosystem in 2011 was different from periods before and after thereported fish health events.The introduction of a large number of barramundi and other fish into the system would havecaused a significant imbalance in the Gladstone Harbour in 2011. These large predatorswould have reduced the number of small fish and other prey items impacting on the foodsupply of other fish species. In addition, the lower salinity and turbidity caused by theflooding would have increased the stress on the ecosystem throughout Gladstone Harbour.The fact that the Phase 2 survey of fish health in Gladstone in 2012 did not find a continuingproblem in any of the candidate fish species supports the hypothesis that the observedissues were caused by a unique set of circumstances that occurred in 2011. This isconsistent with a stressed ecosystem resulting from the freshwater influx, turbidity caused bythe flooding and a large biomass of predators.SharksSkin redness and areas of detached scales associated with parasitic infection were observedon a number of shark species caught during the sampling program from Gladstone and thereference sites. It is unknown whether the numbers of parasites observed on sharks duringthis program are abnormal. However, it is evident that these parasites and associatedpathology are not unique to Gladstone. Severe skin redness was observed as a post-mortemeffect, and this is also not unique to Gladstone.75