With the drastic decline of eastern oyster Crassostrea virginica populations in the Chesapeake Bay due to over-fishing, diseases and habitat destruction, there is interest in Maryland and Virginia in utilizing the non-native oyster species Crassostrea ariakensis for aquaculture, fishery resource enhancement, and ecological restoration. The International Council for the Exploration of the Sea (ICES) recommends that non-native species be examined for ecological, genetic and disease relationships in the native range prior to a deliberate introduction to a new region. Therefore, a pathogen survey of C. ariakensis and other sympatric oyster species was conducted on samples collected in the PR China, Japan and Korea using molecular diagnostics and histopathology. Molecular assays focused on 2 types of pathogens: protistan parasites in the genus Perkinsus and herpesviruses, both with known impacts on commercially important molluscan species around the world, including Asia. PCR amplification and DNA sequence data from the internal transcribed spacer region of the rRNA gene complex revealed the presence of 2 Perkinsus species not currently found in USA waters: P. olseni and an undescribed species. In addition, 3 genetic strains of molluscan herpesviruses were detected in oysters from several potential C. ariakensis broodstock acquisition sites in Asia. Viral gametocytic hypertrophy, Chlamydia-like organisms, a Steinhausia-like microsporidian, Perkinsus sp., Nematopsis sp., ciliates, and cestodes were also detected by histopathology.
This chapter gives an overview on the morphology, host range, life cycle, impact on oyster production, diagnosis, histopathology, physiopathology and control and prevention (selective breeding) of Perkinsus marinus and Haplosporidium nelsoni.
A host-parasite relationship was observed, for the first time, between a piscicolid leech and a species of amphibious goby (Scartelaos tenuis) from an intertidal mud flat in southern Iran. Morphological and molecular investigations assign the leech to Zeylanicobdella arugamensis. Of the 3 endemic and sympatric mudskipper species living in the Persian Gulf (S. tenuis, Boleophthalmus dussumieri, and Periophthalmus waltoni), leeches were only found on S. tenuis (prevalence and mean intensity = 71.4% and 2.3 +/- 2.5, respectively), which is also the most-aquatic mudskipper species. Scartelaos tenuis is not the largest species, but more leeches (> or =4 leeches/host) were found on larger specimens (>12 cm standard length [SL]). Nonetheless, in aquaria, leeches also attached on P. waltoni. This suggests either an ecological partitioning of host-parasite complexes, determined by host habitat selection, or leech limited-resistance to air exposure, or both.
Two species of Trypanosoma, three species of Haemogregarina and one species of Haemohormidium were found in 69 fishes belonging to 28 species. Trypanosoma mackerrasi, sp, nov., from Hemiscyllium ocellatum, measures 125 �m long by 18 �m wide, has no free flagellum, and has the kinetoplast located 37% of the body length from the posterior end. Trypanosoma taeniurae, sp. nov., from Taeniura lymma measures 55 �m long by 4 �m wide and has a free flagellum 9 �m long. Haemogregarina hemiscyllii was found in H. ocellatum, H. tetraodontis parasitised Diodon hystrix, and H. bigemina was found in Ecsenius bicolor. A species of Haemohorrnidium was found in Pomacentrus melanochir, but it could not be identified with certainty.
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