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

was somewhat reduced because post-mortem degeneration can mask subtle changes in gilltissue. This problem was much reduced in grinner and mud crab, because tissues were fixedimmediately following euthanasia of the specimens.Melanomacrophage centres (MMCs) are distinct clusters of cells containing pigment that areknown to increase in size or frequency during conditions of environmental stress or inresponse to starvation or disease (Agius and Roberts, 2003). Age is also known to have asimilar effect on MMCs, however this has been accounted for in our analysis using length asa proxy for age and adjusting the data as though all fish are the same length.Liver MMCs were rated significantly higher (P < 0.05) in barramundi from Gladstone than thereference sites during June/July 2012. They were similarly higher in Gladstone fish thanthose from reference sites caught during April, but the difference was not statisticallysignificant. The fish from Hamilton Point were rated highest for MMCs in both trip one andtwo. There was a significant relationship between MMC scores and mesentery fat (r = -0.57;P < 0.01). Barramundi with lower levels of mesentery fat tended to have higher MMC scores.Barramundi caught from Bundaberg had the lowest ratings for liver MMCs for both samplingtrips.The barramundi from Hamilton Point also had low levels of mesentery fat, low conditionfactor and low hepato-somatic index. This evidence combined suggests that normal feedingmay not have been occurring at the time of capture or in the recent past in the fish caughtfrom Hamilton Point.For further details and statistical analysis of histopathology findings, see Appendix C.Chemical residue testingThe detailed report outlining chemical residue analysis of barramundi and interpretation isfound in Appendix D. This section is a summary of the main findings. The measuredconcentrations of metals in barramundi gills from Gladstone Harbour were similar or lessthan those from the reference sites. The one exception was arsenic, which was twice aslarge in the Gladstone sites than the reference sites; however, this was not a statisticallysignificant difference (P > 0.05). There are no historical data for metals in barramundi liversand gills for similar Queensland estuarine and near-coastal sites available to compare withthe results from the current study.Analysis of barramundi livers showed that the mean measured concentrations of iron andcadmium in fish collected during the first sampling round were significantly (P ≤ 0.05) higherat some Gladstone sites compared to reference sites, and arsenic and zinc were significantlyhigher in Trip 2. The significantly higher levels of these metals were driven by results fromspecimens sampled at Hamilton Point. However, the small number of samples taken at eachsite and trip (n = 5) means that these results should be interpreted with caution. There wasno relationship between the concentrations of these metals and the external signs of health.Arsenic was regularly detected, and iron and zinc were occasionally detected in watersamples collected during the water quality monitoring conducted by the QueenslandGovernment. In contrast, cadmium was rarely detected during the Water Quality MonitoringProgram. The measurement of elevated concentrations of these metals does not necessarilyindicate a toxicological problem, but does indicate exposure to them.Comparison of concentrations of these metals in barramundi livers with toxicological effectsdata did not, overall, indicate that the concentrations in the barramundi liver were of concern.In addition, as there were no significant associations between these metals and observed36