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Pathogenicity Studies with the Fungi Aphanomyces invadans , Achlya bisexualis , and Phialemonium dimorphosporum : Induction of Skin Ulcers in Striped Mullet
Author(s) -
Sosa Emilio R.,
Landsberg Jan H.,
Kiryu Yasunari,
Stephenson Christy M.,
Cody Theresa T.,
Dukeman Angela K.,
Wolfe Heather P.,
Vandersea Mark W.,
Litaker R. Wayne
Publication year - 2007
Publication title -
journal of aquatic animal health
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 52
eISSN - 1548-8667
pISSN - 0899-7659
DOI - 10.1577/h06-013.1
Subject(s) - mullet , biology , saprolegnia , oomycete , mugil , zoospore , fishery , microbiology and biotechnology , fish <actinopterygii> , spore , pathogen
Based on isolations from naturally infected fish in Florida, we investigated the role of the fungi Aphanomyces invadans , Achlya bisexualis , and Phialemonium dimorphosporum in the etiology of ulcerative mycosis (UM) in striped mullet Mugil cephalus . We injected healthy striped mullet subcutaneously with secondary zoospores of four oomycete isolates: two concentrations (50 and 115 zoospores/mL) of SJR (an endemic isolate of Aphanomyces invadans in American shad Alosa sapidissima from the St. Johns River); two concentrations each of CAL (25 and 65 zoospores/mL) and ACH (1,400 and 2,000 zoospores/mL; endemic isolates of Aphanomyces invadans and Achlya bisexualis , respectively, in striped mullet from the Caloosahatchee River); and two concentrations of the ascomycete culture MTZ (2,500 and 3,500 zoospores/mL; endemic isolate of P. dimorphosporum from whirligig mullet M. gyrans in the Matanzas Inlet). All fish injected with either concentration of SJR developed granulomatous ulcers after 8 d and died within 21 d. Eighty percent (8/10) of fish injected with the high dose of CAL developed ulcers after 13 d and died within 28 d, but only 30% (3/10) of fish injected with the low dose of CAL developed ulcers. Four of the ulcerated fish died within 28 d, and the remaining fish were terminated after 32 d. Fish injected with zoospores of Aphanomyces invadans developed ulcers that were grossly and histologically similar to those observed in naturally infected striped mullet with UM from several estuaries or rivers in Florida. These hemorrhagic skin ulcers were characterized by myonecrosis and the presence of mycotic granulomas. None of the fish injected with ACH, MTZ, or sterile water developed ulcers. This study fulfilled Koch's postulates and demonstrated that ulcers could be experimentally induced in striped mullet after exposure via injection to secondary zoospores of an endemic Florida strain of Aphanomyces invadans .