Abstract
Myxosporean parasites of the genus Kudoa are fish parasites of great economic importance, as some species can affect the fish fillet quality by producing macroscopic cysts or generating post mortem myoliquefaction, commonly referred to as ‘soft flesh’. Kudoa mirabilis is a ‘soft flesh’-inducing species originally described based on morphology in the musculature of Trichiurus lepturus from the Indian Ocean. An integrative morphological and genetic characterization of K. mirabilis from the type host caught off the coast of Tanzania is here provided. The spores were stellate with four unequal polar capsules, showing similarities to Kudoa thyrsites. For comparative and validation purpose, K. mirabilis was compared morphologically and genetically with K. thyrsites reference isolates, including new obtained samples from the type host Thyrsites atun caught in the SE Atlantic Ocean. Morphological analyses of spores revealed key diagnostic characters clearly distinguishing the two Kudoa species. Phylogenetic analyses based on SSU and LSU rRNA genes demonstrated that K. mirabilis is a distinct and valid species, representing a sister group to a K. thyrsites subclade that comprises several isolates from Japan and one single isolate from South Africa. This finding raises questions about the true diversity likely hidden in the K. thyrsites complex.
Highlights
Myxosporeans (Cnidaria, Myxozoa) are microscopic endoparasites commonly found in marine and freshwater fish [1,2,3]
The genus Kudoa Meglitsch, 1947 currently consists of around 100 nominal species described from a wide range of fish host species and geographical areas [1,4,5,6]
First signs of abnormally soft and liquefied texture were observed at 36 h of cool storage, in three out of 69 T. lepturus
Summary
Myxosporeans (Cnidaria, Myxozoa) are microscopic endoparasites commonly found in marine and freshwater fish [1,2,3]. The muscle degradation, commonly known as ‘soft flesh’, may irreversibly reduce the quality of the fish fillet and the marketability of the fish product, resulting in economic losses to the seafood industry, as well as loss of consumer confidence [1,4,12] Many Kudoa species have been associated with ‘soft flesh’ in commercially valuable wild and cultured marine fish. One of the most conspicuous ‘soft flesh’-inducing species is Kudoa thyrsites (Gilchrist, 1924), which infects many marine fish species worldwide including Atlantic mackerel (Scomber scombrus) and mahi-mahi (Coryphaena hippurus), as well as Atlantic salmon (Salmo salar) and olive flounder (Paralichthys olivaceus) in mariculture [5,12]. Other ‘soft flesh’-inducing Kudoa species found to infect from economically important fishes include Kudoa musculoliquefaciens (Matsumoto, 1954) in swordfish (Xiphias gladius), Kudoa paniformis Kabata and Whitaker, 1981, in Pacific hake (Merluccius productus) and Kudoa rosenbuschi (Gelormini, 1943) infecting Argentine hake (Merluccius hubbsi) [5,12]
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