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

obvious abnormalities were included to ensure that health conditions not apparent byexternal observation alone could be detected during further laboratory investigations.Statistical analysis was performed to determine significant relationships and trends in thefield and necropsy data, histopathology data and chemical residue data (Appendices B, Cand D respectively).Field observations by Fisheries Queensland: Fish were observed upon capture andassessed visually for external signs of ill health. Data collected included an assessment ofskin discolouration, eye condition, lesions and presence of ecto-parasites. For the purposeof this data collection, skin lesions were distinguished from skin discoloration by observablesigns other than colour change, such as missing scales, ulceration or bleeding (seeAppendix A).Prawns were assessed visually for signs of ill health including shell erosion/lesions and thepresence of parasites. Crabs were assessed for shell abnormalities. Shell lesions weregraded according to the methods described by Andersen (2001).Fish collected using trawl methods (prawns, herring, grinner, Australian threadfin) werenecropsied while onboard the vessel by a veterinarian, and tissue samples were collected forfurther histopathology investigations and residue testing.Laboratory observations by Biosecurity Queensland: Fish were assessed visually forsigns of ill health once received in the lab by a veterinarian. Data collected included, but wasnot limited to, an assessment of skin discolouration, eye condition, lesions and presence ofecto-parasites. Observations of internal organs were made during necropsy, and tissuesamples were collected for further histopathology investigations and residue testing.Crabs were assessed for external shell abnormalities once received in the lab by an aquaticveterinary officer. Shell lesions were graded and location on the carapace recordedaccording to the methods described by Andersen (2003). Further observations were made ofinternal organs during necropsy and, in order to allow a statistical comparison of the fish fromdifferent sites, discrete categories were assigned to capture these observations based onAdams et al. (1993). Chemical residue test results were interpreted by the Department ofScience, Innovation Technology, Innovation and the Arts. For a detailed description of thesampling methods, refer to Appendix A.Histopathology and chemical residue testingA subset of individuals were selected for histopathology examination and chemical residuetesting (Table 1).For barramundi, gills, liver and skin (with muscle) were chosen for microscopic investigation,due to their known sensitivity as indicators of environmental stress. Specifically, thefollowing abnormalities were rated from zero to three to enable quantitative comparisonbetween sites and time points: gill hyperplasia; gill parasites; liver melanomacrophagecentres; skin lesions; and muscle lesions.Barramundi gills and liver were used for chemical residue testing, as they were deemed themost likely tissues to show evidence of short to medium term exposure to contamination.Since there were no significant findings in organic testing of barramundi tissues during Phase1, only metals were tested in Phase 2.19