Thenet, Delphine Julie (2006) Validation of molecular markers and host specificity as identification tools for species determination of Diplozoidae (Monogenea: Oligonchoinea) on British freshwater fish. (MSc(R) thesis), Kingston University, .

Abstract

Diplozoid monogeneans are common freshwater fish parasites which parasitize the gills of cyprinid fish. Identification of diplozoids was previously carried out using morphometric comparison of attachment clamps and central hooks by light microscopy, but this method may now be considered to be unreliable. Problems with identification have led to uncertainty about the diversity and distribution of diplozoid monogeneans in Britain and the extent of their host specificity. This study aimed to identify British species by molecular characterisation and determine the extent of host-specificity in identified diplozoid monogenean species. The identification of specimens in British freshwater fish was carried out by amplifying the Internal Transcribed Spacer 2 (ITS-2) region by Polymerase Chain Reaction (PCR). The amplification of this region of the genome was processed using primers targeting the conserved regions of the ribosomal DNA (5.8S and 28S) flanking the ITS-2. Samples from ‘Abramis brama’ (L.) (bream), ‘Blicca bjoerkna’ (L.) (silver bream), ‘Cyprinus carpio’ (L.) (carp), ‘Carassius carassius’ (L.) (crucian carp), ‘Gobio gobio’ (L.) (gudgeon), ‘Rutilus rutilus’ (L.) (roach), ‘Scardinius erythrophthalmus’ (L.) (rudd) and ‘R. rutilus’ x ‘A. brama’ hybrids were processed for identification. Three genotypes were identified: ‘Eudiplozoon nipponicum’, Goto, 1891, ‘Diplozoon homoion’, Bychowsky & Nagibina, 1959 and ‘Diplozoon paradoxum’ Nordmann, 1832. The study demonstrates that host specificity cannot be used as a marker of identification. ‘Diplozoon homoion’ was found in all hosts tested and ‘D. paradoxum’ and ‘E. nipponicum’ were present in both ‘A. brama’ and ‘C. carpio’. A new host record for ‘E. nipponicum’ on ‘A. brama’ has been found in this study. Accurate identification of British diplozoid species is necessary for the purposes of monitoring fish parasites by regulatory agencies. There is little intraspecific variation between British and Japanese ITS-2.

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