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

Areas of detached scales associated with parasitic infection were observed on a number ofshark species caught during the sampling program from Gladstone Harbour 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 during necropsy,however this was not apparent in freshly caught sharks; redness developed in the hours afterdeath. This post-mortem redness was not unique to Gladstone.Large numbers of prawns and fish were caught on trawlers both in Gladstone Harbour andthe reference sites, with no significant redness or other abnormalities observed.No significant abnormalities were identified from the sampling and necropsy examination ofpelagic species.Histopathology investigation indicated that gill, liver and skin tissue of grinner, and the gill,hepatopancreas and muscle tissue of mud crabs was similar in Gladstone samples toreference sites. Some bleeding and swelling was observed in shark skin from both Gladstoneand reference sites.Chemical residue testing of crabs from both Gladstone and reference sites found asignificant association between aluminium and selenium concentrations, and shell lesions.Given that concentrations of metals in mud crab hepatopancreas were similar to historicaldata from sites across the east coast of Queensland, any effect of these metals on shelllesions is unlikely to be unique to Gladstone. The available data also indicated that the suiteof organic chemicals tested did not contribute to crab disease.Chemical residue testing of muscle tissue from grinner showed no significant differencebetween Gladstone and reference sites.ConclusionsIt is obvious from all the reports that something happened to aquatic life in GladstoneHarbour in 2011. The findings provided in this study indicate that the fish health in GladstoneHarbour had returned to a more normal situation in 2012. Other than the physical damage orrecovery from physical damage, this study found the sampled fish in a health status similar tothat observed in the Bundaberg and Fitzroy reference sites.All industrial activities in Gladstone that were operating in Gladstone in 2011 have continuedto operate, including dredging. The only factor different in 2011 compared to previous yearswas the significant rainfall, the subsequent flooding and the introduction of a significantbiomass of fish from Lake Awoonga. Flooding has also occurred in 2012 and 2013.However, other than continuing reports of barramundi showing physical damage as the resultof being washed over the Awoonga spillway in these flooding events, reports of anyreoccurence of sick fish have not been received by DAFF.The most likely cause of the abnormalities observed during this investigation is the suddenintroduction of barramundi and other fish from Lake Awoonga during December 2010 to early2011. Although barramundi are naturally able to move between fresh and salt waterenvironments, it appears that these fish were overcrowded and unable to feed normally afterthey were suddenly re-located from Lake Awoonga into the Boyne River. The stresspreceded parasitic infestation during the colder winter water temperatures in 2011. TheNeobenedenia infestation subsided as the water temperature increased and fish densityreduced, as shown by improving fish health in late 2011 and 2012.7