The sustainable utilisation of the African clawed frog, Xenopus laevis (Daudin)

Abstract

English: The African Clawed Frog, Xenopus laevis has been used extensively in medical and scientific research. For almost a full century this pipid frog has been exported around the world by thousands. The present study is an attempt to investigate how to manage this important resource of X. laevis that will allow this species to remain a commercially viable resource. The approach in this study was as follows: 1. Market research concerning the use of X laevis to various end-users, conducted locally and overseas, indicated that the oocytes of X. laevis is used to study the molecular aspects of development In South Africa X laevis is in high demand as bait for angling, but lacks a regular organised supply. The use of X laevis in teaching at South African universities has declined over the last decade. The sale of X. laevis as pets is limited and is mostly confined to the United States. 2. The tadpoles of X laevis collected throughout the Free State province and together with specimens from the Southern African Frog Atlas Project collection were staged to determi ne their development and measured. A size-stage graph was obtained that can be used to compare the development of X laevis from other rainfall regions or even captive-raised tadpoles to their natural development in the Free State. 3. Mark and recapture studies were performed on wild X. laevis populations in and around Bloemfontein to investigate their population dynamics Factors that determine the size of a population are: size of the habitat and permanency of the water habitat (semi-permanent or permanent). Regulation of population size by predatory birds becomes significant in semi-permanent habitats when water level is low. It can be concluded that uncontrolled harvesting from natural X laevis sources can easily cause a marked reduction in population size. Experiments on tadpoles and sub-adults were conducted to determine the optimum procedures for rearing X laevis in captivity The volume of water available to tadpoles beyond a density of two tadpoles per litre has an inhibitory effect on development. Factors that further effect tadpole growth rate are: type of enclosure, temperature of environment and tadpole diet. The best growth for sub-adult frogs was obtained by feeding with either Sinking Frog Food (a commercial brand of frog pellets), liver or pet's mince. 5. X. laevis were maintained in captivity for Il months and parasite infections and abundance monitored. The cestode, Cephalochlamys namaquensis was the only parasite to experience a reduction in infection levels, while the only parasite to experience an increase in both prevalence and mean intensity was the mite, Xenopacarus africamts. 6. Various commercial anthelmintics were tested for the elimination of parasites of X. laevis. The delivery technique proved to be as important as the choice of drug itself. The use of drugs to eliminate parasites in X laevis is an effective and affordable method to control parasite infections. 7. It was concluded that to exploit X laevis as a commercial resource on a sustainable basis, efforts should be made to culture the frog following optimum breeding and rearing procedures. The collection method used for frogs from natural sources has to allow for the continued productivity of these populations

Afrikaans: Geen ander dier het ooit tevore die mediese en wetenskaplike navorsing gedien soos die gewone platanna, Xenopus laevis nie. Vir bykans 'n eeu word hierdie padda al uitgevoer na alle dele van die wereld toe. Die doel van hierdie studie is orn die optimale prosedure vir die benutting van X. laevis te ondersoek ten einde te verseker dat die spesie 'n kommersiële hulpbron bly. Die studie is soos volg benader: I. rviarknavorsing oor die benutting van X laevis deur verskeie verbruikers in Suid- Afrika sowel as in die buiteland is gedoen. Die mees veelseggende benutting van x: laevis is die gebruik van die oosiere om die molekulêre aspekte van ontwikkeling te bestudeer. Daar is "n groot aanvraag na x: laevis as aas vir die hengelbebdryf in Suid-Afrika, maar "n georganiseerde verskaffingstelsel ontbreek. Die gebruik van X laevis in onderrig aan Suid-Afrikaanse universireire het in die afgelope dekade afgeneem. Die verkoop van x: laevis as troeteldiere is beperk tot die Verenigde State van Amerika. 2. x: laevis paddavisse wat oor die hele Vrystaat versamel is, tesame met eksemplare uit die Suider Afrika Padda Atlas Projek se versameling, is gemeet en die ontwikkelingstadiums bepaal. 'n Grootte-stadiumgrafiek is opgestel wat gebruik kan word om die ontwikkeling van x: laevis afkomstig van ander reënvalstreke of selfs van paddavisse wat in aanhouding geteel is, te vergelyk met die natuurlike ontwikkeling van paddavisse in die Vrystaat. 3. Merk-en-hervangsstudies is op natuurlike x: laevis populasies van die Bloemfontein area uitgevoer om hul populasiedinamika te bestudeer. Van die faktore wat die grootte van 'n populasie bepaal, is die grootte en standhoudendheid van die habitat. Die regulering van populasiegrootte deur predatoriese voëls is veral wesenlik wanneer die watervlak laag is. Die gevolgtrekking is gemaak dat onbeheerde versameling van X. laevis vanuit natuurlike bronne maklik 'n afname in die populasiegrootte kan veroorsaak. 4. Ten einde die optimale prosedure vir die grootmaak van X. laevis in aanhouding le bepaal is eksperimente op paddavisse en onvolwasse paddas uitgevoer. Die beskikbare watervolume het 'n inhiberende effek op paddavisontwikkeling indien die digtheid van twee paddavisse per liter oorskry word. Verdere faktore wat die groeitempo van paddavisse beïnvloed, is die tipe beskutting, teruperatuur en dieet. Kommersiële padda pille, lewer en troeteldiermaalvleis het die beste groei in onvolwasse paddas gelewer. 5. Parasietgeïnfekteerde X. laevis is vir II maande aangehou terwyl die infeksievlakke en oorlewing gemonitor is. AI die parasiete het in hul gashere oorleef vir die volle duur van die eksperiment. Die platwurm, Cephalochlamys natnaquensis is die enigste parasiet wat 'n afname in infeksievlakke getoon het, terwyl die ImT. Xenopacarus africanus die enigste parasiet is wat toegeneem het in beide persentasievoorkoms en gemiddelde intensiteit. 6. Verskeie kommersiële teenwurmmiddels is getoets VIr hul effektiwiteit teen die parasiete van X. laevis. Dit wil voorkom of die behandelingstegniek en tipe middel ewe belangrik is. Die gebruik van teenwurmmiddels is 'n redelik effektiewe en bekostigbare metode om parasietinfeksies te behandel. 7. Daar is tot die gevolgtrekking gekom dat daar by die teel en grootmaak van X laevis die optimale prosedure gevolg moet word orn te verseker dat hierdie padda . n volhoubare kommersiële hulpbron bly. Verder moet die versamelingsmetode van die paddas vanuit natuurlike bronne van so aard wees dat dit die voortbestaan van die die betrokke populasies kan verseker.