| dc.description.abstract | Diplostomum species metacercariae, are trematodes that pose economic threat to aquaculture globally. Despite their diversity, species identification is difficult owing to their striking morphological similarities. Poor knowledge of diplostomid diversity in fish species coupled with inadequate data from larval parasites in snails represent an obstacle in creation of link sequences to formal description of Diplostomum species. In addition,' effect of the eye fluke Diplostomum on fish growth is not clear because most studies have been conducted in the natural systems where biotic and abiotic factors are uncontrolled. This study aimed to determine the occurrence of Diplostomum parasites in cultured Oreochromis niloticus L., establish the genetic relatedness to other reported Diplostomum parasites, determine the effect on growth and finally to determine prevalence of the infection in intermediate snail vectors at three fish farms in Kibos area. A cross sectional study design was adopted in three fish farms namely Lake Basin Fry Production Centre and two privately owned fish farms (Dr. Mzungu's and Auji fish farms) in Kibos area. Three fish ponds were selected per fish farm using a computer random number generator technique to increase chances of establishing diversity of Diplostomum parasites among the fish. Sixty-four fish were sampled in each pond. The sampling of fish was conducted every three weeks for a period of three months (December 2011 - February 2012). Diplostomum parasites were detected in fish eyes using microscopy to ascertain parasitic indices, genetic discrimination of Diplostomum species was assessed using sequences of the internal transcribed spacer region (ITS1-5.8S-ITS2) and 18S ribosomal genes in 23 diplostornoids, while effect of the parasite on fish was determined using the length - weight relationship formula. A minimum of 100 snails were sampled from the selected ponds using a scoop net and identified based on shell morphology, and screened for Diplostomum infection based on cercariae morphology and behaviour. 52.3% of the fish were positive of Diplostomum parasites. Parasite abundance increased with fish size and later declined in larger fish> 15 em No significant relationship was observed between parasite abundance and fish condition factor in all the study sites (P = 0.516, P = 0.565, P = 0.357 respectively). Phylogenetic analyses ofITS rDNA gene dataset in the metacercariae revealed close relationship to Diplostomum mashonense and D. baeri. Molecular identification using 18S rDNA sequences revealed close relationship to D. compactum, D. phoxini and D. spathaceum. Distribution of vector snails indicated presence of Lymnea, Biomphalaria, Bulinus and Cerratophalus snail species, however; Diplostomum larval communities were reported only in Biomphalaria sp. at a prevalence rate of 21.7%. Presence of metacercariae in fish eyes reared in all the farms together with the high abundance of Biomphalaria sp. shedding cercariae in all the sampled ponds confirmed positive transmission cycle of Diplostomum parasites in Kibos fish farms. Genetic analyses depicted significance of unrecognized genetic diversity. Internal transcribed spacer and 18S rDNA successfully differentiated species of Diplostomum genera suggesting that ribosomal markers are effective genetic markers for inter-species phylogenetic analysis and should be employed in future for identification of diplostomoidea. Diplostomiasis control interventions within fish farms in Kibos area need to prioritize thorough screening of fingerlings from hatcheries before restocking activities in any farm Secondly, snails should be controlled around pond areas by clearing vegetation within the vicinity of.the ponds. | en_US |
