Davies, A.J.

Smit, N.J.

Van As, J.G.

English

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Bull. Eur. Ass. Fish Pathol., 20(3) 2000, 116A Trypanosome From Silver Catfish (Schilbeintermedius) in the Okavango Delta,  BotswanaN. J. Smit, A. J. Davies* and J. G. Van AsDepartment of Zoology and Entomology, Faculty of Natural Sciences, University of the Orange FreeState, Bloemfontein 9300, South Africa.  *School of Life Sciences, Faculty of Science, Kingston Univer-sity, Surrey, UK KT1 2EE.AbstractOf 48 freshwater fishes captured in the panhandle region of the Okavango Delta, Botswana, in1999, only one, the silver catfish , was found to contain a blood parasite. When this trypanosomewas compared with existing records of trypanosomes from the freshwater fishes of tropical andsouthern Africa it was found to most closely resemble Trypanosoma mukasai. Firm identificationof the parasite requires collection of further material from the same source. As far as the authorsare aware, this is the first record of a fish trypanosome from the Okavango Delta and the firstreport of such a parasite from silver catfish.IntroductionBaker (1960), in his paper on thetrypanosomes and dactylosomes of freshwa-ter fish in East Africa, summarised the litera-ture available on trypanosomes infectingfreshwater fish of tropical and southern Af-rica.  Baker (1960, 1961) concluded that ofthose trypanosomes described, there wereprobably only three valid species from Afri-can freshwater fish: Trypanosoma toddi Bouet,1909, Trypanosoma mukasai Hoare, 1932, andTrypanosoma tobeyi Dias, 1952.  Later, Paperna(1996) reported that a species resemblingTrypanosoma mugilicola Becker and Overstreet,1979, existed in the Mugilidae of the lagoonsand rivers of southern Africa.Recently, we were able to examine bloodsmears taken from several species of freshwa-ter fishes captured in the Okavango Delta,Botswana. We report on a trypanosome dis-covered in one of these fishes.Material and MethodsFishes (n = 49) of 12 species in six families,were collected with gill nets stretched acrossdeep lagoons in the panhandle region of theOkavango Delta in June and July, 1999. Fishcaptured by this method were maintained intanks of aerated fresh water until examina-tion, when they were anaesthetised with ben-zocaine.  They were then measured and iden-tified using Skelton (1996).  Heart bloodsmears were taken, fixed in absolute metha-nol, stained with phosphate-buffered Giemsa(pH 6.8) and screened for blood parasites. Anyparasite observed was measured with an eye-piece graticule and stage micrometer, accord-ing to the recommendations of Lom andDykova (1992), and photographed with aZeiss Axoskop 20 photomicroscope.ResultsThe identity, number and length of fishes cap-tured in gill nets are recorded in Table 1. TheyBull. Eur. Ass. Fish Pathol., 20(3) 2000,  117included: tigerfish Hydrocynus vittatusCastelnau, 1861 and silver robber Micralestesacutidens (Peters, 1852) (Characidae); bandedtilapia Tilapia sparrmanii Smith, 1840, thinfacelargemouth Serranochromis angusticeps(Boulenger, 1907), purpleface largemouthSerranochromis macrocephalus (Boulenger,1899), and nembwe Serranochromis robustus(Ghnther, 1864) (Cichlidae); African pikeHepsetus odoe (Bloch, 1794) (Hepsetidae); spot-ted squeaker Synodontis nigromaculatusBoulenger, 1905 and bubblebarb squeakerSyndontis thamalakanensis Fowler, 1935(Mochokidae);   western bottlenose Mormyruslacerda Castelnau, 1861 and bulldogMarcusenius macrolepidotus (Peters, 1852)(Mormyridae); and silver catfish Schilbe inter-medius Rhppell, 1832 (Schilbeidae).Only one species of fish, the silver catfish(Schilbe intermedius), captured in the Deltashowed a blood parasite (Table 1) and this wasa single specimen of a large trypanosomeshown in Fig. 1. The measurements of thistrypanosome are recorded in Table 2.  In theGiemsa-stained blood film, the body of thetrypanosome stained deep blue, though itsfree flagellum, arising from the pointed ante-rior end of the body, was poorly stained.  Theundulating membrane was difficult to discernFigure 1.  Giemsa stained blood film from S.intermedius with trypanosome.  Note its pointedanterior with poorly stained free flagellum (F),nucleus within the deeply stained body, and bluntposterior with rounded kinetoplast. Bar scale = 5µmseicepshsiF .oN DS±htgnelnaeM mmni)egnar( )%(ecnelaverPsutattivsunycordyH 6 8.844 ± )045-503(2.57 )0(6/0sneditucasetselarciM 01 1.75 ± )36-35(3.3 )0(01/0iinamrrapsaipaliT 2 5.731 ± )041-531(5.2 )0(2/0specitsugnasimorhconarreS 1 022 )0(1/0sulahpecorcamsimorhconarreS 1 032 )0(1/0sutsuborsimorhconarreS 3 503 ± )033-082(52 )0(3/0eodosutespeH 1 562 )0(1/0sutalucamorginsitnodonyS 3 402 ± )742-081(4.03 )0(3/0sisnenakalamahtsitnodnyS 1 091 )0(1/0adrecalsurymroM 1 583 )0(1/0sutodipelorcamsuinesucraM 8 6.881 ± )722-071(5.81 )0(8/0suidemretnieblihcS 21 3.312 ± )072-08(2.64 )3.8(21/1latoT 94 )0.2(94/1Table 1. Identity, number and length (mm) of fishes captured in the Okavango Delta, and prevalence ofblood parasites in these fishes.Bull. Eur. Ass. Fish Pathol., 20(3) 2000, 118along some regions of its length, because ofits close proximity to the intensely stainedbody of the trypanosome. The kinetoplast wasprominent and rounded, lying close to theblunt posterior end of the body. The nucleus,which was rounded, stained pink withGiemsa and lay closer to the anterior end ofthe trypanosome than its posterior extremity(Table 2).DiscussionHoare (1932) described T.mukasai fromHaplochromis serranus, Haplochromis cinereusand Haplochromis humilior (Cichlidae) collectedfrom Victoria Nyanza, Uganda. Subsequently,Baker (1960) measured 17 specimens ofHoare’s trypanosome and he noted that thelarger specimens his own trypanosomes fromTilapia and other genera of fishes (Labeo,Bagrus, Mormyrus and Astatoreochromis) inLake Victoria and Lake George, East Africa,closely resembled T.mukasai, except in flagel-lar length. Baker (1960) concluded that hislarge trypanosomes were also T.mukasai andthat the smaller trypanosomes, which hefound in the same fishes, were different formsof the same species.Although we have only one specimen of ourmaterial to compare with others,  the generalmorphology of our trypanosome, its totalbody length (35.4 µm), distance from the pos-terior to kinetoplast (1.2 µm), nucleus length(4.1 µm), body width (4.0 µm) and freeflagellum length (9.2 µm) are all similar tothose of T. mukasai quoted by Baker (1960).Futhermore, the nucleus of our trypanosome,even allowing for measurement from the cen-tre of the nucleus, rather than its anterior edge(as in Baker’s measurements), lies nearer tothe anterior end, as in many examples of Bak-er’s material.Baker (1960) considered that T.mukasai did notdiffer greatly from Bouet’s (1909) T.toddi, ex-cept in having a shorter free flagellum and anucleus slightly, on average, in front of themid-point of the body.  Since our trypanosomehas a flagellar length about equal to that of T.mukasai and a nucleus which is positionedfairly well forward, it resembles T. mukasaimore than T. toddi. Trypanosoma toddi and Dias’ (1952) T. tobeyiappear to differ only in nuclear position (seeBaker, 1960), the nucleus lying more anteriorin T.tobeyi. Baker (1960) considered that T.tobeyi might eventually prove to be a syno-nym of the T. mukasai.The only other trypanosome named from Af-rica is one resembling T. mugilicola (seePaperna, 1996). However, one feature of thistrypanosome is striking. The nucleus of T.mugilicola is only about 6.6µm from the ante-rior end of the body (Becker and Overstreet,tnemerusaeM htgnel )mµ(roiretnaotsuelcundim 1.41roiretsopotsuelcundim 3.12tsalpotenikotsuelcundim 1.02tsalpotenikotroiretsop 2.1htgnelsuelcun 1.4htdiwydob 0.4mullegalfeerffohtgnel 2.9htgnelydoblatot 4.53mullegalfeerfgnidulcnihtgnelllarevo 6.44Table 2. Measurements of Trypanosoma sp. from S.intermediusBull. Eur. Ass. Fish Pathol., 20(3) 2000,  1191979). This characteristic immediately sepa-rates T. mugilicola from T. mukasai because inmost specimens of the latter the nucleus isroughly twice this distance from the anteriorend. Eiras et al. (1995), as a result of their stud-ies in Brazil, suggested that T. mugilicola mightbe synonomous with Trypanosoma froesi Lima,1976.The identity of our trypanosome from theOkavango Delta is difficult to place, since itis based on one specimen. In the absence ofadequate material, we consider that it mostclosely resembles T. mukasai, but we will re-view this opinion should further specimensbe located. As far as we are aware, this is thefirst record of a fish trypanosome from theOkavango Delta region of Botswana and thefirst report of such a parasite from the silvercatfish, Schilbe intermedius.AcknowledgementsThis work forms part of the Okavango FishParasite Research Project sponsored byDebswana Diamond Company and LandRover South Africa. One of us (N.J.S.) waspartly funded by the Canon Collins Educa-tional Trust for Southern Africa.Author’s FootnoteTrypanosoma mukasai has been reported re-cently from African Tilapia nilotica and Clariaslazera, but not from the Okavango (Negm-Eldin M. M & Davies, R.W (1999). Simultane-ous transmission of Trypanosoma mukasai,Babesiosoma mariae and Cyrilia nili to fish bythe leech Batracobdelloides tricarinata. DeutscheTieräztl. Wochenschr. 106, 526-527.)ReferencesBaker, J. R. (1960). Trypanosomes anddactylosomes from the blood of fresh-waterfish in East Africa. Parasitology 50, 515-526.Baker, J.R. (1961). Trypanosomes of Africanfreshwater-fish: an addendum. Parasitology51,263.Becker, C.D. and Overstreet, R.M. (1979). Hae-matozoa of marine fishes from the northernGulf of Mexico. J. Fish Dis. 2, 469-479.Bouet, G. (1909). Sur quelques trypanosomesdes vertébrés à sang froid de L’AfriqueOccidental Française. C.R. Soc. Biol. 66, 609-611.Dias, J.A.T.S. (1952).  Uma nova espécie detripanosoma, parasita do  Clarias gariepinus(Burchell, 1822), peixe africano de água doce.An. Inst. Med. Trop. Lisboa 9, 167-179.Eiras, J.C., Ranzani-Paiva, M.J.T. and Davies,A.J. (1995). Observations on Haemogregarinamugili (Apicomplexa) and Trypanosoma froesi(Sarcomastigophora) from the blood of Mugilplatanus Gunther, 1880 (Pisces: Mugilidae) inBrazil. Res. Rev. Parasit. 55, 173-176.Hoare, C.A. (1932). On protozoal blood para-sites collected in Uganda. With an account ofthe life cycle of the crocodile haemogregarine.Parasitology 24, 210-224.Lom, J. and Dyková, I. (1992). Protozoan para-sites of fishes. In: Developments in Aquacutureand Fisheries Science, 26. Elsevier, Amsterdam-London-New York-Tokyo.Paperna, I. (1996). Parasites, infections and dis-eases of fishes in Africa – an update. CIFA Tech-nical Paper 31, pp. 1 – 220.Skelton, P. (1993) A complete guide to the freshwater fishes of Southern Africa. SouthernBook Publishers (pty) Ltd, Halfway House.

A trypanosome from silver catfish, 'Schilbe intermedius' in the Okavango delta, Botswana

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