Salvatore Mele

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.

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.

Metazoan parasites on the gills of the skipjack tuna Katsuwonus pelamis (Osteichthyes: Scombridae) from the Alboran Sea (western Mediterranean Sea)

The gills of 31 skipjack tuna Katsuwonus pelamis (L.) caught in the Alboran Sea (western Mediterranean Sea) were examined for metazoan parasites, and the gills of 4 specimens from the Balearic Sea (also western Mediterranean Sea) were analysed for comparative purposes. Nine -species of parasites were found, including 8 didymozoid trematodes (Atalostrophion cf. bio-varium, Didymocylindrus filiformis, Didymocylindrus simplex, Didymocystis reniformis, Didymoproblema fusiforme, Didymozoon longicolle, Koellikeria sp. and Lobatozoum multisacculatum) and 1 caligid copepod (Caligus bonito). Koellikeria sp. and L. multisacculatum were not recorded in the Balearic Sea. Most of the parasites (79.2% of all specimens) were didymozoids. Didymozoon longicolle was the dominant species; A. cf. biovarium, D. simplex, D. fusiforme and L. multisacculatum are reported from the Mediterranean Sea for the first time. No correlation was found between the intensity of infection of any parasite species and host size or sex. Most of the parasites, particularly didymozoids, showed a high site-specificity. Significant differences were found between the parasite assemblages of K. pelamis from the Alboran Sea and from the Atlantic Ocean. D. fusiforme, D. longicolle and L. multisacculatum are suggested as potential tags to follow skipjack tuna migrations between the Atlantic Ocean and Mediterranean Sea.

Parasites of the head of Scomber colias (Osteichthyes: Scombridae) from the western Mediterranean Sea

The metazoan parasite assemblage of the head of 30 specimens of the Atlantic chub mackerel (Scomber colias) from the western Mediterranean Sea was analysed. Eight species of parasites were found, four mazocraeid monogeneans: Grubea cochlear (prevalence = 10%), Kuhnia scombercolias (59%), K. scombri (52%), Pseudokuhnia minor (86%); three didymozoid trematodes: Nematobothrium cf. faciale (21%), N. filiforme (41%), N. scombri (7%); and one laerneopodid copepod: Clavelissa scombri (7%). Results were compared with previously published data from 14 localities of the eastern Mediterranean Sea and the Atlantic Ocean, using non-parametric univariate and multivariate analyses, and the whole parasite fauna of S. colias was compared with that of the congeners (S. australasicus, S. japonicus and S. scombrus). Parasites showed to reflect the biogeographical and phylogenetic history of host. From a methodological point of view, the use of both non-parametric univariate and multivariate techniques proved to be effective tools to detect dissimilarities between parasite assemblages.

Metazoan parasites in the head region of the bullet tuna Auxis rochei (Osteichthyes: Scombridae) from the western Mediterranean Sea.

The head region of 72 bullet tuna Auxis rochei from the western Mediterranean Sea (south-east Spain and the Strait of Gibraltar) was examined for parasites. Seven metazoan species were found in the fish from south-east Spain: three monogeneans, two trematodes and two copepods, whereas only three species were isolated in the fish from the Strait of Gibraltar. A comparison of the levels of infection of the parasites according to fish size in south-east Spain showed that the prevalence of Didymozoon auxis and the mean abundance of Allopseudaxine macrova were higher in the larger hosts (range of fork length = 38-44 cm) than in the smaller ones (33-37 cm). A comparison of the parasite infections according to geographical region showed that the mean abundances of Nematobothriinae gen. sp. and Caligus bonito were higher in fish from south-east Spain than in those from the Strait of Gibraltar. A comparison of the parasite fauna of A. rochei from the Mediterranean Sea with the published data on Auxis spp. from the Atlantic, Indian and Pacific Oceans revealed the closest similarity between the Mediterranean A. rochei and the Atlantic A. thazard.

Diagnostic accuracy of the light microscope method to detect the eggs of Cardicola spp. in the gill filaments of the bluefin tuna.

Trematode blood flukes of the genus Cardicola are potentially lethal in bluefin tuna cultures. The present study proposed a new method to detect aporocotylid eggs in tuna gills. Aporocotylid eggs were detected by analysing a pair of gill filaments of five transversal areas of the eight holobranches of one hundred Atlantic bluefin tuna and observed with glycerol and a stereomicroscope with an oblique brightfield. Data were gathered according to holobranches, transversal areas and their combination. Eggs were uniformly distributed among the holobranches, but they had the highest prevalence in the second and fifth transversal areas, which is controversial with respect to previous studies of egg distribution. An abbreviated method called the T-two test, which had the highest sensitivity (96.8%), is proposed for the detection of Cardicola spp. infections instead of the analysis all the holobranches. The T-two test limits the time and cost of the egg parasite screening analysis. The analyses of ten samples could be sufficient to detect the presence of parasites in farmed bluefin tuna; fish from the wild are expected to be less infected and more samples (45) would therefore be necessary.