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

in particular bull sharks, have been observed outside Gladstone both during this survey andduring routine observer trips, it is known that this skin condition is not unique to Gladstone.Furthermore, the degree of redness increases post mortem. It is thought that capturemethods and handling practises of sharks influence the degree of redness exhibited, butfurther work is needed to quantify this effect.The parasitic monogenean, Dermophthirius maccallumi, identified during the program isknown to cause symptoms similar to those observed on many sharks sampled during theprogram, and may also indirectly be the cause of many of the scratch marks around theaffected areas if sharks are ’flashing’ or rubbing themselves on hard substrates in an attemptto rid themselves of the irritation. Given there have been no previous studies onDermophthirius maccallumi on wild sharks that quantify a normal parasite load, it is difficult todetermine whether the number of parasites observed on sharks during this program areabnormal. What is known is that the presence of these parasites and the associated skinlesions are not unique to the Gladstone area.Laboratory findings Phase 2NecropsyA total of 12 sharks were received for laboratory testing, all during April. Only four of thesewere from Gladstone Harbour (three from Calliope River and one from Hamilton Point),seven were caught in the Fitzroy River and one from Bundaberg. The sharks from GladstoneHarbour, particularly the three from the Calliope River, had higher skin condition ratings thanother sharks, although as discussed above this redness was not apparent on capture. It ispossible that subtle differences in handling, such as net mesh size, soak time and time spentin transit, could have influenced this post-mortem skin redness, but particularly with such lownumbers it is not possible to draw any conclusions from these observations.No significant abnormalities were observed internally in any of the sharks during necropsy.HistopathologyLiver, skin and gills from 10 sharks were assessed histologically, including the only four thatwere caught from Gladstone Harbour, five from the Fitzroy River and one from Bundaberg.Common pathology indicators for each tissue were rated from zero to three to allowquantitative comparison to be made. There were no significant abnormalities observed inshark tissues, and there were no significant differences between fish from Gladstone and thereference sites for any tissues. Microscopic examination of skin tissue identified mildinflammation and bleeding in one shark from Bundaberg, mild inflammation in a shark fromHamilton Point, and mild bleeding and degeneration of skin tissue in a shark from theCalliope River. No causal agent was identified for the observed skin redness.Samples collected for chemical residue testing were archived for future testing if required.Banana prawnsThe monitoring program collected information on prawn size, presence and severity ofobserved signs of ill health, as well as commercial catch information supplied by fishers viacommercial logbooks. Samples were collected and provided to Biosecurity Queensland forfurther testing.Sampling sites for banana prawns during Phase 1 and Phase 2 included Gladstone Harbourand waters offshore of Bundaberg and the Fitzroy River (reference sites).60