Pathology of ulcerative mycosis in Atlantic menhaden

The pathology of ulcerative mycosls In naturally affected Atlantlc menhaden BrevoorOa tyrannus 1s described. Ulcerative mycosis is a deep g~anulolnatous dermatopath) (aused by in tec t~on wlth oomycete fungl. The response to this fungal infection was similar to that described for other granulomatous dlseases The posteroventral poltion of the bot1.i was most frequently aftected wlth 67 % of all les~ons observed in this area Lesions appeared to begin as small, focal infections on or near the skln surface which rapidly enlarged and often evtended Into adjacent vlscera In man\ fish, this necrotic mass of tlssue was sloughed, l eav~ng a crater-shaped u l c e ~ Only fish 1~1th small ulcers had dn\ evidence of healing, suggesting that t h ~ s d~sease may cause hlgh mortalit~es In affected populations INTRODUCTION purpose of this artlcle is to provide a detailed description of the ontogeny of 1 M lesions from naturally Ulcerative mycosis (UM) is a recclntly described deraffected menhaden so that it can be differentiated matological dlsease that affects a number of important from other dermatopathies affecting menhaden. estuarine fishes along the Atlantic coast of the United States. I t first became a serious problem in about 1984 when Atlantic niclnhaden Brevoort~a tyrannus were MATERIALS AND METHODS observed with deep necrotic ulcers in several estuarine systems in North Carolina, including those Atlantic menhaden with skin lesions were collected of Pamlico and Albemarle Sounds (Noga & Dykstra primarily from pound nets set on the Pamlico River 1986). Other species were soon observed with UM from July 1984 through July 1986. Fish were also (Noga & Dykstra 19861, and lesions resembling Uh4 obtained from trawl samples collected by the Division were soon reported to occur on fish from Chesapeake of Marine Fisheries and local fishermen in the Bay (Hargis 1985) and the St Johns River estuary in Albemarle Sound, Pamlico h v e r , Neuse River, and Florida (Grier & Quintero 1987). Since its appearance New River (N Carolina, USA). 4 yr ago, UM has continued to cause repeated disease All fish were alive at the time of capture and were outbreaks in these estuarine systems. Its continued necropsied on site. Gross appearance and size of the presence has prompted increasing concern about the lesions were recorded. For light microscopy, tissues impact of the disease on the productivity of the were fixed in either 10 "/o neutral-buffered formalin or estuarine fisheries. In Bouin's fluid. Slun, gills, stomach, intestine, panUlcerative inycosis is a granulomatous disease creas, liver, spleen, heart, muscle, and brain were associated with infection by oomycete fungi. examined. All sections were embedded In paraffin and Aphanomyces has been most commonly cultured from stained with hematoxylin and eosin (H & E). Selected UM lesions, but Saproleynia has also been isolated tissues were also stained with Gomoll methenamine (Dykstra et al. 1986). More than one species in these silver (GMS), periodic acid Schiff (PAS), Giemsa (G) , genera is probably involved. In our initial description Brown and Brenn Gram's stain (B & B), MacCollumof the disease, we provided preliminary information Goodpasture Gram's stain (MG), Fite-Faraco acid-fast on the pathology of UM (Noga & Dykstra 1986). The stain (FF) or Mallory's trichrome stain (T). O Inter-Research/Printed In F R. Germany 190 Dis. aquat. Org. 4 : 189-197, 1988 For electron microscopy, tissues were fixed in McDowell's and Trump's fixative (McDowell & Trump 1976), post-fixed in 1 O/O O s 0 4 in 0.1 M phosphate buffer, pH 7.2, dehydrated through a graded alcohol series, passed through acetone, and embedded in Spurr's resin. Sections were cut, stained with methanolic uranyl acetate and lead citrate, and examined with a transmission electron microscope. Lesion size and location were also recorded on a randomly selected group of menhaden obtained by trawhng in the Pamllco k v e r in order to document the site of the infection on various parts of the body. Lesion size and area were calculated by measuring the widest and narrowest part of each lesion. Location was then recorded on a figure that subdivided the fish into 5 zones (Ej.g. i j. Anaivr~licdi i d l l d ~ r ~ a ~ ks irlcluded the opercular border, the lateral line, and arbitrarily defined distances between various fins. The presence of UM was confirmed using skin scrapings; we considered the presence of aseptate hyphae to be diagnostic.