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

Observational findings Phase 1Between October 2011 and February 2012, catches of banana prawns were observed andinformation on the external signs of health was recorded from a range of sites by FisheriesQueensland observers, as well as during targeted banana prawn surveys.During October 2011, observers noted the small number of banana prawns caught (sixprawns) while aboard a boat fishing for scallops in the Harbour were all in good health.Trawl sampling in Gladstone Harbour in November 2011 caught 85 banana prawns with asingle prawn infected by a parasitic isopod located under the carapace and one prawnshowing signs of minor shell erosion. The remaining 83 prawns were observed to beexternally normal.A further four prawns were collected from the Gladstone Fish Markets. These prawns werecaught on 11 November 2011 in an area opposite Auckland Point Wharf and provided toFisheries Queensland by a local seafood wholesaler. A preliminary examination of one ofthem revealed a large parasitic isopod under the carapace. These prawns were provided toBiosecurity Queensland for further testing.In December 2011, two banana prawns were caught in the trawl sampling in GladstoneHarbour. These prawns were in good condition. In the Fitzroy River, 173 banana prawnswere caught and all observed to be in good condition.During February 2012, Fisheries Queensland observers working aboard commercial fishingboats noted that of the 25 kg of banana prawns caught in the Gladstone Harbour, twoprawns were infected with the gill isopod, while catches in the Fitzroy River (56 kg) andBundaberg (4 kg) were all observed to be in good health.While the above results refer specifically to banana prawns, a number of other prawn specieswere caught during sampling with samples provided to Biosecurity Queensland for furthertesting. Other species included eastern king, endeavour, rainbow and tiger prawns. Based onthe same methods applied in the assessment of banana prawns, no signs of ill health wereobserved in these other species.Laboratory testing Phase 1Prawns showed evidence of shell erosion due to Vibrio spp. A number of prawns includingbanana, eastern king and tiger showed evidence of endoparasite infection by immaturestages of tapeworm and gregarines. These parasites are normal in wild prawn populationsand would not have had a significant impact on the health of prawns (Owen, 1983; Owen &Rothlisberg, 1985). As noted in the field observations, the isopod observed under thecarapace was identified as a bopyrid isopod and is also common in wild prawn populations.Tails of four healthy looking prawns and three prawns with visible abnormalities caused bybopyrid isopods from Gladstone Harbour were tested for chemical residues. Organicstesting found no detectable levels of any chemical. Metal testing showed some differencesbetween the samples, however without replication or any samples from a reference site,meaningful interpretation of this data is not possible.Please refer to www.qld.gov.au/gladstoneharbour for a complete description of the pathologyresults, and the chemical residue test results.63