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

parasites (monogeneans) on the body surrounding the affected areas. While this conditionwas most commonly observed on bull sharks, it was not restricted to this species.A report from an independent expert stated ”it is well established that fish infected bymonogeneans on the skin may ‘flash’ (i.e. rub affected parts of the body against substrate),presumably in an attempt by the host to remove the source of irritation” (Whittington andChisholm, 2008). It is possible that the clinical signs (e.g. skin redness and scratch marksobserved in sharks) could be caused indirectly by the parasites. These parasites occurnaturally, although normal parasite loads are not well documented, so it is not possible todetermine whether observed infections are abnormal.In December 2011, 29 sharks or rays were captured from several sites including the CalliopeRiver (1), the lower reaches of the Boyne River (3) and in Rodds Bay (25). Of these, 14 wereassessed as being healthy with no skin discolouration, 13 sharks showed discolouration on asmall area of the body, one was described as showing a large area of skin discolouration andone displayed skin discolouration over the majority of the body. No sharks or rays showedulcerative lesions.In January 2012, of the 50 sharks and rays captured, 12 were caught in the Fitzroy River (allbull sharks) while the remaining came from sites within Gladstone including the CalliopeRiver (7), Hamilton Point (1), the Spoil Ground (11) and Rodds Bay (19). All the sharks fromthe Fitzroy River had ecto-parasites and skin discolouration. Within the Gladstone sites,some of the black tip whaler, bull, lemon, milk and weasel sharks caught had skindiscolouration. Most of these sharks also had ecto-parasites.In February 2012, at sea observations were conducted on two net fishing operations for twoconsecutive nights. The fishing was conducted at Rodds Bay and at Colosseum (halfwaybetween Rodds Bay and the mouth of the Boyne River). Over the four nights, the fisherscaught 52 sharks and rays. Of the 21 bull sharks caught, 19 had ecto-parasites and skindiscolouration. Four of the other sharks and rays exhibited redness on the ventral surface.Laboratory testing Phase 1Tissue from a total of 21 sharks was examined microscopically during Phase 1, with 21bacteriology tests. Five necropsies were conducted on whole sharks.Shark species examined during Phase 1 included lemon shark, bull shark, pig eye shark,whitecheek shark, blacktip whaler shark, graceful whaler shark and narrow sawfish. Thesharks examined had scale pocket hyperaemia (pockets of reddening), dermal haemorrhage(bleeding of the skin) and epidermal necrosis (cell death). When sections were taken and theskin lesions were observed under a microscope, observations included congestion in theconnective tissue immediately below the epidermal basement membrane, occasionalhaemorrhage into the epidermis and/or skin surface, and a mild inflammatory cell infiltrationinto the outer layer of the dermis. No bacterial or fungal pathogens were found that couldexplain these skin conditions on the sharks.Monogenean parasites found on the skin of several bull sharks were identified asDermophthirius maccallumi from the family Microbothriidae. Similar parasites were found ongraceful whaler sharks and pig eye sharks. This genus is known to cause disease in captivesharks, including excess mucous production and ulcerated skin lesions. This disease canlead to secondary infection by bacteria or viruses, but has also been implicated in skinlesions, denticle loss and other clinical signs in wild sharks without co-infection by bacteria orviruses.57