Abstract
Simple SummaryIn this study, we detected Kudoa hexapunctata in Pacific bluefin tuna (Thunnus orientalis) individuals that did not show any gross pathology lesions. Giemsa staining was used to identify clearer lesions than haematoxylin and eosin (H&E) staining that is used in general histological analysis. K. hexapunctata was separated through molecular biological methods, other than haematolocial and histological analysis. Individuals infected with K. hexapunctata showed relatively low haemoglobin (Hb) and haematocrit (Ht) values, and histological analysis revealed clear pseudocysts in the abdominal and dorsal muscles.The consumption of fish and shellfish worldwide is steadily increasing, and tuna is a particularly valuable fish species. However, infection caused by Kudoa spp. is causing problems in many fish including the Pacific bluefin tuna (Thunnus orientalis), and there is much controversy about the association of these infections with foodborne disease. In this study, using haematological and histological analyses of the blood and internal organs (liver, spleen, kidney, heart, stomach, intestine, gill, and muscle) of Pacific bluefin tuna cultured in South Korea, infection with Myxosporea was first identified, and molecular biological analysis was conducted. In this study, Kudoa hexapunctata was finally identified. The Pacific bluefin tunas analysed in this study did not show any gross pathology lesions, such as visible cysts and/or myoliquefaction, of infection with this species. The histological analytical results can provide guidelines for the identification of K. hexapunctata. In the case of K. hexapunctata-induced infection, unlike other countries, such as Japan, there have been no reports in South Korea, and this study is the first to detect K. hexapunctata infection in Pacific bluefin tuna cultured in South Korea. The correlation between K. hexapunctata and food poisoning is not yet clear, however, it is thought that continuous observation of its infection is necessary.
Highlights
Because fish and shellfish products have exhibited nutritive benefits and because of the increasing demand for healthy food, the consumption of fish and shellfish products is increasing annually [1,2].Among fish, tuna has a very high commercial value in many countries [3]
Of Pacific bluefin tunas and haematological results arethe presented in theFive other tuna samples withvalues an average of 15.02 g/dL
The Pacific bluefin tuna (Thunnus orientalis) used in this study did not shown any common gross pathology lesions, such as white or yellow cysts or myoliquefaction in the abdominal and/or dorsal muscle, that have been seen in olive flounder (Paralichthys olivaceus) infected by Kudoa septempunctata [20]
Summary
Tuna has a very high commercial value in many countries [3]. Parasitic diseases in fish can cause foodborne diseases in humans, according to the literature, which indicates that Kudoa septempunctata is a potential threat to human health [4,5,6]. Of interest, are K. septempunctata in olive flounder (Paralichthys olivaceus), K. hexapunctata in tuna, and their possible. Animals 2020, 10, 1705 implication in causing foodborne diseases [4,5,6]. Japanese patients exhibiting clinical diarrhoea had eaten tuna in which Kudoa hexapunctata was detected [7]. According to Suzuki et al [7], K. hexapunctata is likely to be one of the causes of foodborne disease; there is still no clear evidence. Ohnishi et al [9] said that
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