Gill monogeneans of the chub mackerel, Scomber japonicus from Madeiran waters of the Atlantic Ocean, Portugal

Five species of monogeneans were recovered from the gill filaments of 181 chub mackerel, Scomber japonicus, from the Madeiran waters of the Atlantic Ocean, Portugal, during 2004/2005. The monogenean Pseudokuhnia minor showed the highest prevalence (98.68%) and a mean intensity of 28.23, followed by Kuhnia scombri (prevalence of 43.71% and mean intensity of 2.69) and K. scombercolias (prevalence of 39.1% and a mean intensity of 1.81). Kuhnia sprostonae and Grubea cochlear were rare, occurring in only one and five fish hosts respectively. No correlation between fish host length and mean intensity of infection with the three most abundant monogeneans was found. However, significant differences in prevalence and abundance were found in relation to date of sampling for P. minor, and all parasites were aggregated in their distribution.     

Kuhnia sprostonae Price, 1961 and K. scombercolias Nasir & Fuentes Zambrano, 1983 (Monogenea: Mazocraeidae) and their microhabitats on the gills of Scomber australasicus (Teleostei: Scombridae), and the geographical distribution of seven species of gill Monogenea of Scomber spp.

As a result of an extensive survey of monogeneans on the gills of scombrid fishes of the genus Scomber, especially S. australasicus in Australia, it has been shown that Kuhnia sprostonae as previously defined by Rohde & Watson is, in fact, two distinct species, namely K. sprostonae Price, 1961 and K. scombercolias Nasir & Fuentes Zambrano, 1983. K. sprostonae inhabits the pseudobranchs of Scomber scombrus in the North Sea, S. japonicus off Madeira and S. australasicus in Australian waters, and shows considerable variability in the lengths of the hamuli and the genital hooks. K. scombercolias occurs on the main gills of S. japonicus and S. australasicus in many regions of the Atlantic and Indo-Pacific. Other species of gill monogeneans on Scomber spp. are Kuhnia scombri, Pseudokuhnia minor, Grubea cochlear and G. australis. A damaged juvenile monogenean of unknown status was recovered only once in the Mediterranean. The geographical distribution of gill monogeneans of Scomber spp. is discussed.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of nine microsatellite loci from the chub mackerel, Scomber japonicus (Perciformes, Scombridae)

The stock abundance of the chub mackerel Scomber japonicus - a very important species for fisheries, particularly in Japan - in the Pacific Ocean off Japan has remained at a low level. For studying the population genetics of the chub mackerel, we isolated nine polymorphic microsatellite loci (12-31 alleles/locus; expected heterozygosity, 0.762-0.983) from this species. Cross-species amplification indicated that eight of the nine microsatellite loci in the blue mackerel S. australasicus were polymorphic and functional.     

Size differences in hamuli of Kuhnia scombri (Monogenea: Polyopisthocotylea) from different geographical areas not due to differences in host size

Hamuli of Kuhnia scombri from Scomber australasicus and S. japonicus from several localities in the Pacific Ocean show marked differences in length. Hamuli from large fish are slightly longer than those from small fish caught in the same geographical area (northern New Zealand). Differences correlated with host size are much less than those associated with geographical area and may be due to infections acquired in different localities. Taxonomic studies of Monogenea must take geographical variation and, to a lesser degree and in at least some species, effects of host size into consideration.     

What can metazoan parasites reveal about the taxonomy of Scomber japonicus Houttuyn in the coast of South America and Madeira Islands?

The metazoan parasites of four populations of the chub mackerel Scomber japonicus were analysed from two localities in the Atlantic Ocean (Madeira Islands, Portugal, and Rio de Janeiro, Brazil) and two localities in the Pacific Ocean (Callao, Peru, and Antofagasta, Chile), collected during 2002 and 2003. A total of 373 fish specimens were studied and 34 metazoan parasite species were obtained. Parasites identified from the populations of chub mackerel studied could be separated into three categories: parasites with a wide distribution, present in the Pacific and Atlantic, parasites proper of the Pacific Ocean and parasites proper of the Atlantic Ocean. The analyses of some highly specific parasites of the genus Scomber ( i.e. monogeneans of the genus Kuhnia and didymozoid digeneans) strongly suggest the need for a revision of the taxonomic status of chub mackerels from the Atlantic and Pacific coast of America. The results demonstrated the usefulness of parasites as adequate tools to clarify the taxonomic status of their hosts.     

Three species of copepods parasitic on the blue mackerel Scomber australasicus Cuvier (Actinopterygii: Perciformes: Scombridae) from southern Japan,with description of a new species Colobomatus itoui n. sp. (Cyclopoida: Philichthyidae)

Systematic Parasitology - The blue mackerel Scomber australasicus is one of the major commercial fishes consumed in southern Japan. Three species of parasitic copepods were collected from S....     

Microsatellite DNA markers for population-genetic studies of blue mackerel (Scomber australasicus) and cross-specific amplification in S. japonicus

Blue mackerel (Scomber australasicus) is targeted by large-scale purse-seiners in the western North Pacific, and its stock structure is still contentious. Herein, we described 10 polymorphic microsatellite loci for blue mackerel. The number of alleles among 32 individuals surveyed ranged from five to 27 (average of 16.2 alleles per locus). Departures from Hardy-Weinberg expectation were observed at two loci. Cross-specific amplification in the congener, S. japonicus, was successful, except for one locus, revealed to be diagnostic for these congeners. These microsatellite loci will be useful tools to address queries in population genetic structure, fishery management unit and taxonomic species status in the genus Scomber.     

Differential population structuring of two closely related fish species, the mackerel (Scomber scombrus) and the chub mackerel (Scomber japonicus), in the Mediterranean Sea

Population genetic structures of the mackerel (Scomber scombrus) and chub mackerel (Scomber japonicus) were studied in the Mediterranean Sea. Fragments of 272 bp (S. scomber) and 387 bp (S. japonicus) of the 5'-end of the mitochondrial control region were sequenced from spawning individuals collected off the coasts of Greece, Italy, Spain, and Portugal. High levels of mitochondrial control region haplotypic diversity (> 0.98) were found for both Scomber species. Nucleotide diversity was higher in the mackerel (0.022) than in the chub mackerel (0.017). Global F(ST) values were also higher and significant in the mackerel (0.024, P < 0.0001) as opposed to the chub mackerel (0.003, P > 0.05). Molecular variance analyses showed differential genetic structuring for these two closely related species. There is extensive gene flow between Mediterranean Sea and Atlantic Ocean populations of chub mackerel, which are organized into a larger panmictic unit. In contrast, Mediterranean Sea populations of mackerel show some degree of genetic differentiation and are structured along an east-west axis. The analysed eastern Mediterranean Sea mackerel populations (Greece, Italy) are clearly separated from that of the western Mediterranean Sea (Barcelona), which forms a panmictic unit with eastern Atlantic Ocean populations. The genetic structures of both species showed asymmetric migration patterns and indicated population expansion.     

Combined ribosomal DNA and morphological analysis of individual gyrodactylid monogeneans

A method is presented for the isolation and analysis of hamuli, marginal hooks, and bars from individual gyrodactylid monogeneans using scanning electron microscopy (SEM), while simultaneously processing parasites for rDNA analysis using the polymerase chain reaction (PCR). The haptors of ethanol-fixed gyrodactylids were protease digested to liberate hooks for SEM, whereas DNA extracted from the bodies was used for PCR. The method resulted in hooks and hamuli being prepared from more than 90% of Gyrodactylus turnbulli individuals, a significant improvement on previously published digestion-based SEM techniques. PCR on the same parasites was less successful, but sequence data were obtained from 50% of individuals. Amplification of rDNA internal-transcribed spacer regions from individual worms used for SEM gave PCR products consistent with those predicted from our previous sequence analysis. This method allows the correlation of morphology and DNA sequence from the same individual and can be applied to ethanol-fixed material, such as field collected and museum specimens.     

Origin and evolution of the hamuli in the monogeneans

The hypothesis of the origin and evolution of the hamuli in monogeneans is proposed. It is suggested that the hamuli originated as the adult attachment organs of protomonogeneans inhabited the gills of the first vertebrates. Primarily they were represented by two lateral pairs of large hooks disposed anterior to the larval haptor. The fundamental direction in the evolution of monogeneans was the concentration of all attachment structures on the growing haptor. It the course of this evolutionary process, the hamuli onchoblasts migrated to the haptor, in which they had reached the position in the hind part of the haptor. The neotenic evolution of the Dactylogyridea and Gyrodactyloidea resulted in the forming new hamuli pairs. The hooks of opposite sides of the haptor are joined in a single complex within each side by the transverse plates (bars). So the presence of 4 hamuli is plesiomorphy for all the monogeneans and the presence of the transverse bars and new hamuli pairs are apomorphy for the Dactylogyridea and Gyrodactyloidea, whose evolution was linked with that of the Teleostei. The origin of the new hamuli pairs and transverse bars in the Dactylogyridea and Gyrodactyloidea appears to be a convergence.     

Phylogenetic differentiation between Atlantic <Emphasis Type="Italic">Scomber colias</Emphasis> and Pacific <Emphasis Type="Italic">Scomber japonicus</Emphasis> based on nuclear DNA sequences

In the classical taxonomy, three Scomber species are distinguished: S. scombrus, S. australasicus, and S. japonicus. Yet, some fish taxonomists have recently recognized Scomber colias, inhabiting the Atlantic Ocean, as a separate species from S. japonicus, distributed in the Pacific Ocean. Such proposal was based on significant mitochondrial DNA divergence as well as great phenotypic variation among individuals from these two ocean basins. However, in the absence of nuclear DNA data this issue remains still controversial. In this study, a phylogenetic analysis of nuclear 5S rDNA sequences was performed. A total of 30 individuals of S. colias collected in the Atlantic and 34 specimens of S. japonicus from the Pacific were characterized. Moreover, nine individuals of Pacific S. australasicus and eight of Atlantic S. scombrus were included. Maximum likelihood, maximum parsimony, and neighbor-joining analyses revealed the presence of two well-supported distinct clades corresponding to S. colias and S. japonicus, respectively. Altogether, morphologic and genetic data are in agreement with the recognition of two different species, S. colias in the Atlantic, and S. japonicus in the Pacific.     

Morphology and geographical variation of Pseudokuhnia minor n.g., n.comb. (Monogenea: Polyopisthocotylea)

A new genus, Pseudokuhnia, is established for Kuhnia minor, family Mazocraeidae. It differs from Kuhnia in the presence of two dorso-lateral vaginae, supported by surface ridges; differently shaped large genital hooks, large hamuli and ovary; an opisthaptor which is ventral to and well separated from the body proper; and a rudimentary antero-supplementarium of the clamps. The Atlantic population of P. minor differs from the Pacific population mainly in the larger size of the hamuli and the smaller size of the large and small genital hooks.     

The occurrence and infection dynamics of Anisakis larvae in the black-scabbard fish,Aphanopus carbo,chub mackerel,Scomber japonicus,and oceanic horse mackerel,Trachurus picturatus from Madeira,Portugal

Larval stages of Anisakis spp. (Nematoda: Anisakidae) were found encapsulated or free in the viscera and abdominal cavity of the black-scabbard fish, Aphanopus carbo, chub mackerel, Scomber japonicus and oceanic horse mackerel, Trachurus picturatus in Madeiran waters. The prevalence of infection reached 97.2% for A. carbo, 69.5% for S. japonicus and 62.5% for T. picturatus. Considerable differences in parasite intensities between A. carbo and both S. japonicus and T. picturatus were found, with mean intensities up to 69.6 in A. carbo, while in the other two fish hosts the intensity reached only a maximum of 2.6. These differences were probably due to different feeding behaviours of the hosts. Intensities of Anisakis sp. in A. carbo were high irrespective of sex and season. No relationship between host length and prevalence of infection was observed for A. carbo, while for S. japonicus a weak positive significant relationship was found.     

The parasite fauna of the chub mackerel (Scombridae: Scomber japonicus Houttuyn, 1782) in the central-eastern Atlantic (Atlantic coast of the Northern Africa and the Azores Archipelago banks)

The parasite fauna of the chub mackerel Scomber japonicus Houtuym, 1782 was studied from the neritic areas of Morocco, Western Sahara, Mauritania and from the banks of the Azores Archipelago (the Great Meteor Bank, the Hyeres Bank and the Irving Bank) in 1994-2001. Twenty eight species of parasites of following group have been were found: Coccidia (1 species), Microsporidia (1), Myxosporea (4), Monogenea (4), Cestoda (5), Trematoda (5), Acanthocephala (1) and Nematoda (6). The differences between mackerel parasite fauna in the neritic areas and from of the Azores Archipelago banks were established. Peculiarities of the mackerel parasite fauna in two areas (Morocco--Western Sahara and Mauritania) corroborate the hypothesis that two populations of chub mackerel are available: "Sahara-Moroccan" and "Senegal-Mauritanian". Ontogenetic variability of parasite fauna was related to food demands of mackerel and its feeding habits in the areas Morocco and Mauritania. Kudoa histolytica has negative influence on the commercial value of S. japonicus. These parasites were localized in the muscles of mackerel from Mauritania (40%, TL = 20-25 cm). Parasites being dangerous for human health were presented by larvae of Bolbosoma sp. (occurred on the banks of the Azores Archipelago), Anisakis simplex and Contracaecum sp. (occurred in all areas investigated).     

Rapid PCR-RFLP method for discrimination of imported and domestic mackerel

With the ever-decreasing domestic fishery catch of Japanese mackerel Scomber japonicus, alternative Atlantic mackerel Scomber scombrus has been increasingly imported and currently accounts for approximately 34% of mackerel consumption in Japan. As there is no morphologic difference between the species after removal of their skin, not only fresh and frozen fillets but also processed seafood of S. scombrus are frequently marketed with mislabeling as S. japonicus. In this study, a rapid and reliable polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis was developed to discriminate imported mackerel S. scombrus and domestic mackerel S. japonicus. PCR amplification for the nuclear 5S ribosomal DNA nontranscribed spacer was performed using Scomber-specific primers. Direct digestions of the PCR products using either PvuII or HaeIII restriction enzymes generated species-specific profiles, indicating that both enzymes enable the accurate identification of S. scombrus and S. japonicus. This robust and reproducible method can serve as molecular-based routine food inspection program to enforce labeling regulations.     

Ultrastructure of the primary gill lamellae of Scomber australasicus

The ultrastructure of the primary epithelium, and the efferent half of the subepithelium, of the primary gill lamellae of slimy mackerel ( Scomber australasicus ) is described. The following cells are identified and described: light nucleated epithelial cells (surface and basal), dark nucleated cells, mucous cells, acidophilic cells, type 1 cells, type 2 cells, type 3 cells and chloride cells in the epithelial region, and subepithelial cells A and B, fibroblasts, chondrocytes, cells of the wall of efferent blood vessel and some blood cells in the subepithelium.     

Ontogeny of swimming speed, schooling behaviour and jellyfish avoidance by Japanese anchovy Engraulis japonicus

The ontogeny of swimming speed, schooling behaviour and jellyfish avoidance was studied in hatchery-reared Japanese anchovy Engraulis japonicus to compare its life-history strategy with two other common pelagic fishes, jack mackerel Trachurus japonicus and chub mackerel Scomber japonicus. Cruise swimming speed of E. japonicus increased allometrically from 1·4 to 3·9 standard length (L(S) ) per s (L(S) s(-1) ) from early larval to metamorphosing stage. Burst swimming speed also increased from 6·1 to 28 L(S) s(-1) in these stages. Cruise speed was inferior to that of S. japonicus, as was burst speed to that of T. japonicus. Engraulis japonicus larvae were highly vulnerable to predation by moon jellyfish Aurelia aurita and were readily eaten until they reached 23 mm L(S) , but not at 26 mm L(S) . Schooling behaviour (indicated by parallel swimming) started at c. 17 mm L(S) . Average distance to the nearest neighbour was shorter than values reported in other pelagic fishes. The relatively low predator avoidance capability of E. japonicus may be compensated for by their transparent and thus less conspicuous body, in addition to their early maturation and high fecundity.     

An SEM study of the haptoral sclerites of the genus Gyrodactylus Nordmann, 1832 (Monogenea) following extraction by digestion and sonication techniques

Techniques for the preparation of haptoral sclerites of Gyrodactylus species for scanning electron microscopy are described. Enzymatic digestion using pepsin allows fresh, frozen and alcohol-fixed material to be examined, but some sclerites, such as the dorsal and ventral bars, are lost. Sonication of fresh and frozen material retained these accessory bars, including the ventral bar membrane, the guard or sickle filament loop on the marginal hooks and even on some occasions ligaments associated with the sclerites. The sclerites of Gyrodactylus spp. from Gasterosteus aculeatus (L.) (three-spined stickleback), Oncorhynchus mykiss (Walbaum) (rainbow trout) and Salvelinus alpinus (L.) (charr) are described from SEM observations following the use of these preparation techniques, and the articulation between the hamuli and bars is commented upon.     

The use of geometric morphometrics in understanding shape variability of sclerotized haptoral structures of monogeneans (Platyhelminthes) with insights into biogeographic variability

The sclerotized attachment organ of monogeneans has been widely used to address fundamental questions in ecology and evolution. However, traditional morphometric techniques appear to be partially inadequate and non-optimal. Traditional linear measurements mainly provide information on the size of sclerites but provide very little information, if any, on their shape. The shape of sclerites is indeed virtually unexplored and its implication for ecological and evolutionary processes remains to be analyzed. This study aims to both introduce and illustrate the use of geometric morphometrics in order to study sclerites of monogeneans in a biogeographic context. To do this, we investigated morphological variation patterns among four populations from the Pacific Ocean and six monogenean species through traditional and geometric morphometric techniques. Unlike the traditional method, the geometric morphometric method yielded a high percentage of individuals correctly classified to the four populations, providing strong evidence for phenotypic variability, divergence and local adaptation among islands without evolutionary constraint. Moreover, the traditional method also resulted in inconsistent interpretations of shape variations. This study highlighted the limitations that may arise when using traditional morphometric techniques and emphasizes that considerable information about the shape of sclerotized haptoral parts is added by using geometric morphometrics. Given the prominent taxonomic, ecological and evolutionary role of the haptor for characterizing monogeneans, we ultimately discuss the potential broad use of geometric morphometrics in a wide variety of ecological and evolutionary contexts. This powerful approach might allow a more robust estimation of the extent to which traditional evolutionary theories based on size of sclerites are congruent with their shape.     

玫氏新本尼登虫扫描电镜观察(单殖吸虫纲,分室科)

报道寄生于福建海水养殖鱼类高体蜥的玫氏新本尼登虫(单殖吸虫纲,分室科)的扫描电镜观察。虫体体表无棘,前吸器和后吸器盘状。副甲片、前钩和后钩位于鞘内,副甲片尖状,前钩和后钩弯钩状,边缘小钩呈辐射状排列于后吸器边缘。