Morphological characterisation and identification of four species of Cardicola Short, 1953 (Trematoda: Aporocotylidae) infecting the Atlantic bluefin tuna Thunnus thynnus (L.) in the Mediterranean Sea

Abstract

Blood flukes of the genus Cardicola Short, 1953 are considered the most potentially pathogenic parasites in bluefin tuna cultures. Morphological study and genetic analyses of the ribosomal internal transcribed spacer ITS-2 and the mitochondrial cytochrome c oxidase 1 (cox1) gene fragments revealed the occurrence of four aporocotylid species (C. forsteri Cribb, Daintith & Munday, 2000, C. orientalis Ogawa, Tanaka, Sugihara & Takami, 2010, C. opisthorchis Ogawa, Ishimaru, Shirakashi, Takami & Grabner, 2011 and Cardicola sp.) in 421 Thunnus thynnus (L.) from the Western Mediterranean (274 fished from the wild and 147 from sea-cages). Cardicola opisthorchis was the most abundant species, with higher prevalence in the cage-reared fish than in those fished in the wild (21 vs 6%, p < 0.05). Adults of three species were recovered: C. forsteri from both gills and heart, C. opisthorchis from heart and C. orientalis from gills. The secondary gill lamellae were profusely infected by eggs of C. orientalis. A fourth species was found in four tunas, based on the molecular analyses of eggs apparently indistinguishable in size and shape from the eggs of C. orientalis. The findings provided evidence that infections with Cardicola spp. differed in relation to locality, host origin (wild vs cage-reared) and site of infection. It is necessary to estimate the possible different pathogenic effects of each species of Cardicola in order to take appropriate control measures.

Molecular and morphological identification of Cardicola (Trematoda: Aporocotylidae) eggs in hatchery-reared and migratory Atlantic bluefin tuna ( Thunnus thynnus L.)

“…Our results show that C. forsteri extrauterine eggs in the gills have a fusiform shape with a mean length and mean width of 80.14 and 24.25 µm, respectively. Additionally, as reported byPalacios-Abella et al (2015) …”

“…For egg detection within filaments we used the protocol described by Palacios-Abella et al (2015). For this purpose, 6 gill filaments of cultured ABT and 10 gill filaments of fattened ABT were removed and thoroughly washed with distilled water to remove excess blood.…”

“…This has been demonstrated for pathologies associated with trematodes belonging to genus Cardicola, parasites infecting the blood system of fishes, considered the most dangerous pathogens in tuna farms from Japan and Australia (Colquitt et al, 2001;Ishimaru et al, 2013;Shirakashi et al, 2012a). Cardicola adults are located in the heart and branchial vessels (Cribb et al, 2000;Ogawa et al, 2010;Palacios-Abella et al, 2015) and eggs get trapped in the gill capillaries, where they hamper circulation, interfere with gas exchange and cause physical damage to the gills . Up to four different Cardicola species, C. opisthorchis, C. orientalis, C. forsteri and Cardicola sp., have been recently reported in wild ABT caught in the Western Mediterranean and in specimen fattened along Mediterranean coast (Palacios-Abella et al, 2015).…”

“…Cardicola adults are located in the heart and branchial vessels (Cribb et al, 2000;Ogawa et al, 2010;Palacios-Abella et al, 2015) and eggs get trapped in the gill capillaries, where they hamper circulation, interfere with gas exchange and cause physical damage to the gills . Up to four different Cardicola species, C. opisthorchis, C. orientalis, C. forsteri and Cardicola sp., have been recently reported in wild ABT caught in the Western Mediterranean and in specimen fattened along Mediterranean coast (Palacios-Abella et al, 2015). In association with the increase in tuna farming and culturing of juveniles, parasitic infections have increased in frequency becoming a significant issue, particularly among juveniles (Ogawa et al, 2010(Ogawa et al, , 2011Shirakashi et al 2012a).…”

“…clearly provides a better estimate of the species composition of Cardicola in the gills of ABT than the screening of gill filaments Palacios-Abella et al (2015). reported the presence of adult blood flukes of C. opisthorchis and C. forsteri in wild and fattened ABT although they failed to find eggs in the gill arteries probably due to the thickness of the afferent side of the filament in the large tuna examined.…”