Infections by Kudoa ciliatae (Myxozoa: Myxosporea) in Indo-Pacific whiting Sillago spp.

Infections by Kudoa ciliatae Lom, Rohde & Dykova, 1992 were detected in 141 (32%) of 444 Indo-Pacific whiting Sillago spp, caught in Moreton Bay, Australia. The parasite was detected in the type host, S. ciliata (in 14% of 73 fish), and from 2 new hosts, S, maculata (46% of 264) and S. analis (9% of 107). Prevalence of infection in S. maculata was greatest in autumn (100%) and lowest in spring (10%), the seasonal differences being positively correlated to host size (more prevalent in larger fish caught in autumn). Intensity of infection ranged from 1 to 45 cysts per fish (mean 7.6) and the cysts measured up to 2.5 mm in length. Most cysts were located on the serosal surface of the intestinal tract extending into the circular smooth muscle layer. The majority were found in the distal third of the intestine, often in groups of 2 to 5 cysts. Parasites were also found for the first time in the pyloric caeca, intestinal mesentery and liver. Calcified cysts were occasionally detected in S, ciliata and S, analis

Deconstructing dams and disease: predictions for salmon disease risk following Klamath River dam removals

The health of fish populations and the river systems they inhabit have broad ecological, cultural, recreational, and economic relevance. This is exemplified by the iconic anadromous salmonid fishes native to the West Coast of North America. Salmon populations have been constrained since the mid nineteenth century by dam construction and water reallocation. In the Klamath River (Oregon and California, USA), a series of dams built in the early-mid 20th century cut the basin in two and blocked anadromous fish access to more than 600 river kilometers. This dramatic loss of habitat, coupled with infectious diseases and resulting epizootics, have impacted the wellbeing of these salmonid populations. In 2023-2024, the Klamath River will undergo the largest river restoration project in US history. Removal of the four lowermost dams will cause profound physical changes to the river, including flow, water temperature, and channel geomorphology. The dam removals will reconnect the lower and upper portions of the basin, and provide fish passage after a century of segregation. Reestablishment of upstream and downstream fish movements will also alter the occupancy and abundance of the salmonid hosts and their pathogens. The increased habitat availability and longer migration routes will increase duration of pathogen exposure and potential impacts on juvenile survival and adult pre-spawn mortality. However, restoration of more natural flow and sediment regimes will decrease overall fish disease risk by disrupting complex parasite life cycles. To better understand these multifarious, competing factors, we review the salmonid species in the Klamath River, and provide an overview of their historical pathogen challenges and associated diseases and use this as a framework to predict the effects of dam removals on disease dynamics. Our review and predictions are a synthesis of expertise from tribal biologists, fish health specialists and fish biologists, many of whom have lived and worked on the Klamath River for decades. We conclude with recommendations for expansion of current pathogen monitoring and research efforts to measure changes in host-pathogen dynamics basin-wide

Ultrastructure and small-subunit ribosomal DNA sequence of Henneguya lesteri n. sp (Myxosporea), a parasite of sand whiting Sillago analis (Sillaginidae) from the coast of Queensland, Australia

Henneguya lesteri n. sp, (Myxosporea) is described from sand whiting, Sillago analis, from the southern Queensland coast of Australia. H. lesteri displays a preference for the pseudobranchs and is typically positioned along the afferent blood vessels, displacing the adjoining lamellae and disrupting their normal array, The plasmodia appeared as whitish-hyaline, elliptical cysts (mean dimensions 230 x 410 mum) attached to the oral mucosa lining of the hyoid arch on the inner surface of the operculum. Infections of the gills were also found, in which the plasmodia were spherical, averaged 240 x 240 mum in size and were located on the inner hemibranch margin. The parasites lodged in the gill filament crypts and generated a mild hyperplastic response of the branchial epithelium, In histological sections, the plasmodium wall and adjoining ectoplasm appeared as a finely granulated, weakly eosinophilic layer, Ultrastructurally, this section of the host-parasite interface contained an intricate complex of pinocytotic channels. H. lesteri is polysporic, disporoblastic and pansporoblast forming. Sporogenesis is asynchronous, with the earliest developmental stages aligned predominantly along the plasmodium periphery, and maturing sporoblasts and spores toward the center. Ultrastructural details of sporoblast and spore development are in agreement with previously described myxosporeans. The mature spore is drop-shaped, length (mean) 9.1 mum, width 4.7 mum, thickness 2.5 mum, and comprises 2 polar capsules positioned closely together, a binucleated sporoplasm and a caudal process of 12.6 mum. The polar capsules are elongated, 3.2 x 1.6 mum, with 4 turns of the polar filament. Mean length of the everted filament is 23.2 mum, Few studies have analyzed the 18S gene-of marine Myxosporea. In fact, H. lesteri is the first marine species of Henneguya to be characterized at the molecular level: we determined 1966 bp of the small-subunit (18S) rDNA, The results indicated that differences between this and the hitherto studied freshwater Henneguya species are greater than differences among the freshwater Henneguya species

Parasite fauna of Australian marine oligochaetes

Volume: 46Start Page: 555End Page: 57

New data on Thelohanellus nikolskii Achmerov, 1955 (Myxosporea, Myxobolidae) a parasite of the common carp (Cyprinus carpio, L.): The actinospore stage, intrapiscine tissue preference and molecular sequence

Thelohanellus nikolskii, Achmerov, 1955 is a well-known myxozoan parasite of the common carp (Cyprinus carpio L.). Infection regularly manifests in numerous macroscopic cysts on the fins of two to three month-old pond-cultured carp fingerlings in July and August. However, a Thelohanellus infection is also common on the scales of two to three year-old common carp in ponds and natural waters in May and June. Based on myxospore morphology and tissue specificity, infection at both sites seems to be caused by the same species, namely T. nikolskii. This presumption was tested with molecular biological methods: SSU rDNA sequences of myxospores from fins of fingerlings and scales of older common carp were analysed and compared with each other and with related species available in GenBank. Sequence data revealed that the spores from the fins and scales represent the same species, T. nikolskii. Our study revealed a dichotomy in both infection site and time in T. nikolskii-infections: the fins of young carp are infected in Summer and Autumn, whereas the scales of older carp are infected in Spring. Myxosporean development of the species is well studied, little is known, however about the actinosporean stage of T. nikolskii. A previous experimental study suggests that aurantiactinomyxon actinospores of this species develop in Tubifex tubifex, Müller, 1774. The description included spore morphology but no genetic sequence data (Székely et al., 1998). We examined >9000 oligochaetes from Lake Balaton and Kis-Balaton Water Reservoire searching for the intraoligochaete developmental stage of myxozoans. Five oligochaete species were examined, Isochaetides michaelseni Lastochin, 1936, Branchiura sowerbyi Beddard, 1892, Nais sp., Müller, 1774, Dero sp. Müller, 1774 and Aelosoma sp. Ehrenberg, 1828. Morphometrics and SSU rDNA sequences were obtained for the released actinospores. Among them, from a single Nais sp., the sequence of an aurantiactinomyxon isolate corresponded to the myxospore sequences of T. nikolskii

Density of the Waterborne Parasite Ceratomyxa shasta and Its Biological Effects on Salmon

The myxozoan parasite Ceratomyxa shasta is a significant pathogen of juvenile salmonids in the Pacific Northwest of North America and is limiting recovery of Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon populations in the Klamath River. We conducted a 5-year monitoring program that comprised concurrent sentinel fish exposures and water sampling across 212 river kilometers of the Klamath River. We used percent mortality and degree-days to death to measure disease severity in fish. We analyzed water samples using quantitative PCR and Sanger sequencing, to determine total parasite density and relative abundance of C. shasta genotypes, which differ in their pathogenicity to salmonids. We detected the parasite throughout the study zone, but parasite density and genetic composition fluctuated spatially and temporally. Chinook and coho mortality increased with density of their specific parasite genotype, but mortality-density thresholds and time to death differed. A lethality threshold of 40% mortality was reached with 10 spores liter(⁻¹) for Chinook but only 5 spores liter(⁻¹) for coho. Parasite density did not affect degree-days to death for Chinook but was negatively correlated for coho, and there was wider variation among coho individuals. These differences likely reflect the different life histories and genetic heterogeneity of the salmon populations. Direct quantification of the density of host-specific parasite genotypes in water samples offers a management tool for predicting host population-level impacts.Keywords: Klamath River-basin, Infective stage, Rainbow trout, Myxosporean parasite, Oncorhynchus-tshawytscha, Coho salmon, Temperature, Host, Myxozoa, Juvenile Chinook salmo

Klamath River Thermal Refuge Provides Juvenile Salmon Reduced Exposure to the Parasite <i>Ceratonova shasta</i>

<p>Salmon in the Klamath River of northern California contend with water temperatures that reach stressful and sometimes lethal levels during summer, forcing them to seek thermal refuge at coolwater tributary junctions. During migration, these fish also encounter a range of pathogens that affect their survival. A significant myxozoan parasite, <i>Ceratonova shasta</i>, causes enteronecrosis in salmon, and this disease increases in severity as temperature and parasite dose increase. In complementary laboratory and field studies, we examined how the use of a thermal refuge (an area at least 2°C colder than the main stem) affects progression of enteronecrosis in juvenile Chinook Salmon <i>Oncorhynchus tshawytscha</i> and Coho Salmon <i>O. kisutch</i>. We compared fish use, water temperature, and <i>C. shasta</i> concentration in a refuge at the Beaver Creek–Klamath River confluence during the summer in 2008 and 2010. Salmonid numbers ranged from 190 to 2,125, and temperatures were 2–8°C cooler than in the main stem. In June and July of 2008, parasite levels in the refuge were lower than in the main stem, where they exceeded 100 spores/L. In 2010, main-stem parasite levels did not exceed 10 spores/L, and levels in the refuge were lower in June. In the laboratory, we compared the effect of fluctuating and constant temperature treatments on mortality rates of Chinook Salmon and Coho Salmon exposed to <i>C. shasta</i>. Under most experimental conditions, fluctuating temperature, within the range experienced by fish using thermal refuges (15.5–21°C), had no significant effect on disease progression compared with a constant midrange temperature (18.5°C) with equivalent degree-day accumulation. We propose that in the Klamath River thermal refuges can function as disease refuges from enteronecrosis by (1) providing areas of decreased <i>C. shasta</i> exposure and/or (2) alleviating disease effects as a result of relatively lower water temperatures. The trend of increasing water temperatures suggests that juvenile salmon will rely even more on these critical habitats in the future.</p> <p>Received October 9, 2015; accepted February 25, 2016 Published online June 22, 2016</p