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

Barramundi found in freshwater impoundments generally have high fat levels. WithinGladstone Harbour, high levels of mesentery fat appeared to be an indicator of fish that hadrecently passed over the Awoonga Dam spillway. All five fish from Lake Awoonga hadgreater than 50% mesentery fat. Of the fish examined from the Boyne River, those with highmesentery fat tended to also have lesions. In total, 19 of the 20 fish with lesions in the BoyneRiver had greater than 50% mesentery fat. Of the remaining 16 fish from the Boyne Riverwith no observed lesions, only one had greater than 50% mesentery fat. Elsewhere inGladstone Harbour, 43 of the 49 barramundi examined had no observable mesentery fat(see Figure 14). The proportion of fish with notable mesentery fat decreased across all sitesbetween April and June/July 2012. In both reference sites, barramundi had relatively highlevels of mesentery fat, which did not appear to be related to lesion scores.Mesentary fat levelsNone 50% caecum covered 100% caecum coveredNumber of Fish20181614121086420L0 L0 L1 L0 L2 L0 L2 L0 L1 L2 L3 L4 L0 L2 L3 L4LakeAwoongaCalliopeRiverHamilton Point Rodds Bay lower Boyne River upper Boyne RiverSite and Lesion ScoreFigure 14. Levels of mesentery fat in barramundi from Gladstone sites, according to their lesion scores asrecorded during necropsy.HistopathologyDue to technical difficulties, there were some samples of barramundi that were not able to beproperly evaluated for the analysis of skin, so the skin histology data could not be included inthe statistical analysis. All other values were combined to allow comparison of cumulativescore as a very crude measure of overall health for each fish. Liver lipid scores were alsocategorised in this way, but were not tallied with other scores because liver storagevacuolation is not an abnormality.Due to the variation in time taken to transport barramundi specimens to the lab and toperform necropsies, there were varying levels of post-mortem degeneration in the tissues.Pathologists were provided with time between capture and necropsy for each specimen toenable estimation of this effect, and quantified only the abnormalities deemed not attributableto post-mortem degeneration.The barramundi from Lake Awoonga had the lowest score for gill hyperplasia, gill parasites,muscle lesions and cumulative score. All five fish from Lake Awoonga were rated moderatefor liver lipid, which is consistent with necropsy findings of relatively high condition factor,mesentery fat and hepato-somatic index in these fish. The differences between fresh andsalt water fish are expected, given the substantial difference between habitats.Gill hyperplasia was significantly higher in barramundi from the reference sites compared toGladstone in April 2012 sampling. There were no significant differences between sites in theJune/July sampling trip. Gill hyperplasia is an abnormal increase in the cell numbers and canbe a sensitive indicator of water-borne irritants. The sensitivity of this analysis in barramundi35