Abstract
Galaxias maculatus (Jenyns, 1842) is a widespread freshwater fish and an important component of the economically important whitebait fisheries across the Southern Hemisphere. We report a new myxosporean parasite (Cnidaria: Myxozoa) infecting the kidney of G. maculatus from northwestern Patagonia (Argentina). Ortholinea lauquen sp. nov. was characterized using myxospore morphology, morphometrics and small subunit rDNA (ssrDNA) sequence data. Our ssrDNA phylogenetic analyses showed that O. lauquen sp. nov. is a member of the oligochaete-freshwater urinary tract clade and basal to a clade containing 4 different spore morphotypes (Chloromyxum, Myxidium, Zschokkella, Hoferellus). We explored host-parasite relationships at the macro- and microscale by analyzing the distribution, tissue tropism and pathology of O. lauquen sp. nov. Prevalence was relatively low (7%) by microscopy, but PCR detection revealed hidden levels of infection (49%), with the highest detection in lakes Morenito and Moreno (63-90%, Río Negro Province). The only locality negative by both microscopy and PCR was the Caleufu River (Neuquén Province), suggesting differences in fish life history traits (landlocked vs. potamodromous) or preference of the putative obligate invertebrate host for lentic habitats. O. lauquen sp. nov. sporulates in the renal tubules and occasionally in the glomerular space. The plasmodia frequently occluded the tubule lumina, and cellular necrosis and disintegration of the epithelium were observed. O. lauquen sp. nov. could represent a potential threat to G. maculatus culture under intensive farming conditions.
Highlights
Galaxias maculatus (Jenyns, 1842) (Osmeriformes: Galaxiidae; known as inanga by the Maori or puyen chico in Spanish) is one of the most naturally widely distributed freshwater fish (Berra et al 1996)
G. maculatus is one of the species regarded as whitebait and is an important component of this commercial and recreational fishery as food fish in New Zealand and Chile (David et al 2014, Froese & Pauly 2018, Gomon & Bray 2019)
Myxozoans are a widespread group of parasitic cnidarians that have complex life cycles which alternate between an intermediate host and a definitive host (Eszterbauer et al 2015)
Summary
Galaxias maculatus (Jenyns, 1842) (Osmeriformes: Galaxiidae; known as inanga by the Maori or puyen chico in Spanish) is one of the most naturally widely distributed freshwater fish (Berra et al 1996). Myxozoans are a widespread group of parasitic cnidarians that have complex life cycles which alternate between an intermediate host (vertebrates, mainly fish) and a definitive host (annelid or bryozoan) (Eszterbauer et al 2015) These spore-forming parasites are responsible for diseases that can cause significant impacts on fish health in both wild populations and aquaculture and affect commercial fisheries (Dyková & Lom 1982, Molnár et al 1989, Hedrick et al 1993, Whipps 2011). The known species form a polyphyletic group scattered through the oligochaete−freshwater urinary tract clade of myxozoans (Fiala 2006, Rangel et al 2014, 2017, Holzer et al 2018) This heterogeneous clade contains at least 7 different genera with very different spore morphologies. Few data exist on the host−parasite interaction of members of the genus Ortholinea in the urinary system of their hosts
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