Bull. Eur. Ass.Fish Pathol. 6 (3),76, 1986 FURUNCULOSISIN SEA-REAREDATLANTIC SALMON, Salmosalar L. COLONIZATION OF THE GILL EPITHELIUM By D.W. BRUNo Furunculosis is caused bY a Gram- furunculosisoutbreak in Atlantic salmon, negative, non-motile bacterium, Salmosalar rearedin a seacage. 38 Aeromonas sslmonicida, traditionally In 1985this laboratorydiagnosed farmed affectingfish in freshwater (Richardsand outbreaks of furunculosis in 20 Roberts, 1978), although pure cultures salmonidsin Scotland,an increaseof have been obtained from a strictly marine and 23 on thoseconfirmed during the two period species, the sable fish, AnoPloPoma precedingyears. During this 9090 outbreaksoccurred in seawater, fimbria (Evelyn, 1971).The pathology of of these as an furunculosis is typical of a haemorrhagic thus highlighting furunculosis water caged septicaemia and is well described in increasingproblem for sea case rainbow trout, Salmo goirdneri and fish in Scotland.Diagnosis in each of ,4. brown trout, Solmo trutta in fresh water followed the isolation and culture (TSA). (Klontz, Yasutake and Ross, 1966; solmonicidqon tryptic soy agar bY light Fergusonand McCarthy, 1978;McCarthy This was suPPorted on buffered and Roberts, 1980).Darkening in colour, microscopicialobservations sections. lethargy, fin congestion, furuncle formalin fixed and stainedtissue five moribund development and slight exophthalmos During October 1985 2.0 and may be recorded. Internally tissueshave Atlantic salmonweighing between a sea cage beennoted as soft, friable and congested 2.5Kg were removedfrom (McCarthy and Roberts 1980). Necrosis farm. The water temperaturewas lloC, reduced,and a few of reticulin sheathcells, mucosalsurfaces feedingresponses were recorded. An and kidney tubules is common and mortalities had been taken from the accompaniedby proliferation of bacterial inoculumwas asceptically and streakedonto colonies in the spleen, heart, liver and kidney,liver and spleen at22"C for 48 hours' kidney (McCarthy and Roberts' 1980). TSA andincubated a buffered formal Transmission through stock Tissueswere fixed in stained bY movementsand inter-year class transfer saline and sections (H&E) and within farms are identified as primary haematoxylin and eosin fluorescentantibody meansof spreadingthe pathogen(Munro' Gram. An indirect conductedon adjacent 1982),however little is known about the test (FAT) was werecovered precise route bY which fish become sectionsas follows;sections salmonicidaantiserum infectedwith .4. salmonicida. with a rabbit A' phosphatebuffered saline This communication refers to diluted lOx in in severalchanges colonization of the gill epithelium by ,4. for l0 minutes,washed with a similarly salmonicido in a naturally occurring of buffer and covered Bull. Eur. Ass. Fish Pathol. 6 (3), 77, 1986 diluted fluorescein labelled sheep anti- pathology has been reported in seawater rabbit immunoglobulin, also for l0 in other salmonids. In the amago, minutes. (Oncorhynchus rhodurus) in salt water Gross post-mortemexamination of the initial gill epithelial lesions led to lamellar moribund Atlantic salmon revealed thrombosis (Mjazaki and Kubota, 1975) petechiation in the body cavity. The and the extensionof the infection to the spleenwas enlarged and the liver pale. heart, liver, spleenand kidney. Ferguson Histologically in the kidney there was and McCarthy (1978) observed small haemorrhagingbetween the tubules with colonies on the lamellae of naturally scatteredmicro-bacterial colonies in the infected captive brown trout where the haemopoietictissue. Tubular endothelial cellular reaction was minimal. However ql cells were sloughed into the lumen. The Klontz et (1966) and Thorpe and spleen was congestedand the ellipsoids Roberts (1972) found no significant mostly destroyedby coloniesof bacteria. lesions of the gills of experimentally Bacterial colonies occurred between the infected rainbow trout and naturally hepatic cords and were surrounded by infectedbrown trout. In the presentstudy necrotic and dying host cells. The all the fish were suffering a systemic ventricle and atrium contained bacterial infection thus the source of the bacteria colonies, but there were no apparent colonizing the gill surface may have been lesions. There was sloughing of the of internal or externalorigin. However in intestinal mucosa. The pancreas and a recent casea colony of A. salmonicida caecawere normal. On the gills, bacterial was only located on the secondary gill colonieswere recordedon the surfaceand filaments of a post-smolt. McCarthy at the base of the secondary lamellae (1971) has speculatedthat entry of this wheresome necrosis of the epitheliumand pathogen into the host may result from pyknosis of the interlamellar cells was abrasion of the lateral integument or via noted (Fig. l). An increasein eosinophilic the gastrointestinaltract. However, the granular cells occurred in the central exactroute is not known. Growth of large filamentsand some of the gill epithelium colonieson the gill surface, such as those had been stripped (Fig. l). Specific described,could provide a ready meansof fluorescencewas recordedby the bacteria entry for A. solmonicida and represent a on the gills and by those in the other primary site of infection. tissuesto the FAT test confirming the identity asA. salmonicida(Fie.2). A pure was obtained on TSA from culture Summary visceralorgans. Colonization and multiplication by Aeromonas This is the first report of colonization salmonicida, the causativeagent of furunculosis, on gill reared in sea the gill filaments of farmed Atlantic th: epithelium of Atlantic salmon of water is reported. lt is proposed that this route can salmon by A. solmonicids in sea water. provide a site for primary infection by l. The pathologyof furunculosisin Atlantic salmonicida. reared in sea water is similar to salmon Acknowledgements that described in fresh water' The author would like to thank Dr A.E. Ellis for Furunculosis and an associated gill supplyingthe antisera. ", Bull. Eur. Ass. Fish Pathol. 6 (3), 78, 1986 References McCarthy, D.H. and Roberts, R."I. (1980). Furun- Evelyn, T.P.T. (1971). An aberrant strain of the culosis of fish-the present state of our know- bacterial fish pathogen Aeromonos solmontctaa ledge. ln Advances in Aquatic Microbiology isolated from a marine host' the sablefish/z4no- oI Volume 2, (ed. M.R. Droop and H.W. Jannasch) plopoma fimbria), and from two specles pp. 293-341. Academic Press, London' culiureA Pacific salmon. J. Fish Res' Board Miyazaki, T. and Kuboto, S'S' (1975)' Histopath- Can. 28, 1629-1634. ological studies on furunculosis in amago' Fish Ferguson,H.W. and McCarthy, D.H' (1978)'Histo- Path. 9, 213-218. of furunculosisin brown trout Sa/zo nathology A.L.S. (1982).Furunculosis-an old prob- tutta L. J. Fish Dis. I' 165-174' Munro, lem facing a new industry, Proc. Roy' Soc' Crischkowsky,R.S. (1981).Furunculosis' In Alaskan Edinb.8lB, r77-184. Wildlife Diseases(ed. R.A. Dieterich),pp' 383- Richards, R.H. and Roberts, R'-/. (1978). The 395. Universityof Alaska, Fairbanks' Alaska' bacteriologyof teleosts.ln Fish Pathology (ed' Ktontz, C.W., Yosutake, lV.T. and Ross, A'J' R.J. Roberts). pp' 183-204, Bailliere Tindall: Bacterial diseasesof the salmonidaein trS6el. London. ih. *.rt".n United States: Pathogenesis of Ross,A.J. and Smith, C'A. (1974).Effect of tem- fumnculosisin rainbow trout' Am' J Vet' Res' perature on tlre survival of Aeromonas lique- 27. 1455-1460. Aeromonas salmonicida, Chondrococcus Mccarthy, D.H. \191':'). Some ecological aspects faciens, colum naris and Pseudom o nas f lu o rescens' P t og' of the bacterial fish pathogen-'Ae/'otnona; (ed' Fish-Cult. 36, 5l-52' salrnonicido. ln Aquatic Microbiology Thorpe, J.E. and Roberts, R.J. (1972) An F.A. Skinner and J.M. Skewan), Society for airomonad epidemic in the brown tto:ul (Salmo Applied Bacteriology No 6, pp' 299-324' trutta L.) J. Fish Biol. 4' 441-451. AcadernicPress, London' Author's address: DepartmentofAgriculture&FisheriesforScotland,MarineLaboratory,VictoriaRoad,Torry' AberdeenAB9 8DB' Scotland' Bull. Eur. Ass.Fish Pathol. 6 (3),79, 1986 WStS:w$$,liIW:1:I! [,ocirti<rnt:tl tlerorrronas saltrtortit'idaon the gill lamellae of a naturally infected Atlantic salnrcrrr,Solttro sulur reared in salt $ater, (H&E, x360). Iti-g.2: Location of Aeromonos salmonicida by an indirect fluorescentantibody technique, (x570)..