The potential of parasite transfer to an alternative host during short periods of cohabitation was explored. The work described in this paper suggests that either the field sampling process itself or the subsequent transportation of multiple fish species in the same container, may affect the correct allocation of parasites to hosts, and the diagnosis, management and control of gyrodactylosis in a variety of fish. Gyrodactylus infected specimens of three-spine sticklebacks Gasterosteus aculeatus, minnows Phoxinus phoxinus and stone loach Barbatula barbatula from one Scottish river were cohabited with one another in small volumes of water for 3 h. The study found that a small number of Gyrodactylus spp. transfer to atypical hosts. This study indicates that personnel involved in fish disease surveillance programmes should be aware of the possible consequences, in terms of inter-host transfer, of transporting multiple species in the same transport vessel. Diagnosticians should be aware of the facts that fish may act as temporary/paratenic hosts and that the apparent gyrodactylid fauna present following transport may not reflect that encountered under normal circumstances.
Cultured Ryukyu ayu Plecoglossus altivelis ryukyuensis was found to be infected with a microsporidian parasite on Amami Oshima Island in January 2009. The parasite formed numerous cysts on the visceral organs and skin of the diseased fish. High temperature seemed to suppress the development of the parasite; in 2009 and 2010, the disease occurred in the 0-year fish from April to August, and afterwards the prevalence decreased dramatically in September and October. These characteristics well resembled glugeosis in ayu P. altivelis altivelis in other areas of Japan. This parasite seems to be indigenous to Amami Oshima Island, because it was detected in the museum specimens of wild Ryukyu ayu caught in 1991. Average dimensions of spores from Ryukyu ayu were slightly shorter and wider than those of Glugea plecoglossi, but the ranges of the measurements were overlapped. From the above characteristics and molecular analysis of SSU rRNA, it was concluded that the present microsporidian was included genus Glugea, but the specific identity remained to be clarified.
Infection of a blood fluke, possibly Cardicola sp. (Digenea: Aporocotylidae), in reared Atlantic bluefin tuna Thunnus thynnus was investigated. Parasitological analyses included visual examination of the heart for the presence of adult fluke and stereomicroscopic and histopathological analyses of the gill to assess the presence of lesions caused by parasite eggs. No adult flukes were found in the hearts. Some of the gills exhibited small white to yellow foci involving single filaments. Blood fluke eggs were found in gill tissue sections of 29.6% of sampled tuna. A slight inflammatory response was observed around most of these eggs, while occasionally individual eggs were encapsulated by a granulomatous reaction. Despite the absence of remarkable pathological effects in the infected tuna, blood flukes combined with other agents may cause major problem.
We examined the prevalence of Flavobacterium psychrophilum infection in wild ayu Plecoglossus altivelis in four rivers in Miyagi Prefecture that have not been artificially stocked with juvenile ayu. The isolation rates of F. psychrophilum from apparently healthy ayu ranged from 58 to 100% (mean 89%). The majority of isolates were classified into the A/S genotype. All of the examined isolates were highly virulentto juvenile ayu. Our results suggested that bacterial cold water disease was present in wild ayu populations, even in rivers without a history of ayu stocking.
In this pilot study, juvenile rainbow trout were experimentally challenged with the microsporidian Loma salmonae to determine the effects of immunostimulation with β-1,3/1,6 glucan administered in the feed at 200 mg/kg of feed, and immunosuppression with dexamethasone at 300 mg/kg of feed when these were administered in the early stages of infection. Six weeks after oral exposure to Loma spores, control fish developed a mean of 34.8 spore filled xenomas per gill arch; those which had received β glucan had significantly fewer xenomas (23.6) whereas those receiving dexamethasone had significantly more (43.0). Paradoxically, when fish received both β glucan and dexamethasone in any of three temporal combinations, xenoma numbers were significantly higher (51.0-65.1) even when compared to fish receiving only dexamethasone.