Larval trypanorhynchs (Platyhelminthes: Eucestoda: Trypanorhyncha) from black-scabbard fish, Aphanopus carbo and oceanic horse mackerel, Trachurus picturatus in Madeira (Portugal)

Four different types of trypanorhynch postlarvae were found attached to the stomach mucosa, external stomach wall or free in the body cavity of two marine fishes from Madeira, namely blackscabbard fish, Aphanopus carbo and oceanic horse mackerel, Trachurus picturatus. Morphological features shown by SEM indicated that the postlarvae belonged to the species Tentacularia coryphaenae, Sphyriocephalus tergestinus, Nybelinia lingualis and possibly N. yamaguitii. Prevalence [mean intensity (range)] of T. coryphaenae, S. tergestinus and Nybelinia spp. in A. carbo (n = 135) was 12.6% [1.65 +/- 1.27(1-6)], 5.9% [1.57 +/- 0.79 (1-3)] and 2.2% [1.33 +/- 0.58 (1-2)] respectively. The prevalence of T. coryphaenae and S. tergestinus showed some seasonality, with a rise in prevalence of T. coryphaenae corresponding to a decrease in prevalence of S. tergestinus. However these differences were not significant. In T. picturatus (n = 304) only N. lingualis was found at a prevalence of 9.6%. Both S. tergestinus and N. lingualis were recovered only from the stomach mucosa or external stomach wall, while T. coryphaenae was observed either attached to the stomach mucosa or free in the visceral cavity of the fish. The paper presents the first scanning electron micrographs (SEM) of Sphyriocephalus tergestinus and a new geographical record of N. lingualis in T. picturatus.     

Helminth parasites of the oceanic horse mackerel Trachurus picturatus Bowdich 1825 (Pisces: Carangidae) from Madeira Island, Atlantic Ocean, Portugal

The helminth parasite fauna of the oceanic horse mackerel Trachurus picturatus Bowdich 1825, caught off the Madeira Islands was composed of six different taxa. Prevalence and abundance of larval Anisakis sp. (Nematoda: Anisakidae) and Nybelinia lingualis (Trypanorhyncha: Tentaculariidae), the most common parasite taxa, were 24.3%, 0.9 and 37.9%, 0.7, respectively. Bolbosoma vasculosum (Acanthocephala: Polymorphidae) and the monogeneans Heteraxinoides atlanticus (Monogenea: Heteraxinidae) and Pseudaxine trachuri (Monogenea: Gastrocotylidae) were comparatively rare. The depauperate helminth fauna of the oceanic horse mackerel at Madeira compared to other geographical regions of the north-eastern Atlantic, namely the Azores banks and the West African coast, may be attributed to the paucity of nutrients off oceanic islands and to a low density of the fish population.     

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.     

Steroidogenesis in ovarian follicles of chub mackerel, Scomber japonicus

We incubated different radiolabeled steroid precursors with intact chub mackerel ovarian follicles to clarify the synthetic pathways of steroid hormones during vitellogenesis and following final oocyte maturation (FOM). During vitellogenesis, estradiol-17beta (E2) was synthesized from pregnenolone via 17-hydroxypregnenolone, 17-hydroxyprogesterone, androstenedione, and testosterone. The physiological significance of the intermediate metabolites of E2 in the ovarian follicles was examined by comparing follicular steroidogenesis between gonochoric and hermaphroditic fish species. After vitellogenesis, the steroidogenic pathway shifted from E2 to maturation-inducing hormone (MIH) production owing to the inactivation of 17,20-lyase and the activation of 20 beta-hydroxysteroid dehydrogenase. Of the new steroids produced during FOM, 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) was most effective at inducing germinal vesicle breakdown in vitro. Circulating levels of 17,20beta-P increased specifically around the time of germinal vesicle migration, while another FOM-specific 20beta-hydroxylated progestin, 17,20beta,21-trihydroxy-4-pregnen-3-one, was present at consistently low levels during FOM. These results indicate that 17,20beta-P is the MIH of chub mackerel.     

Three-dimensional analysis of finlet kinematics in the chub mackerel (Scomber japonicus)

Finlets, which are small non-retractable fins located on the body margins between the second dorsal and anal fins and the caudal fin of scombrid fishes, have been hypothesized to improve swimming performance. The kinematics of three posterior finlets of the chub mackerel, Scomber japonicus, were examined using three-dimensional measurement techniques to test hypotheses on finlet rigidity and function during steady swimming. Finlet bending and finlet planar orientation to the xz, yz, and xy planes were measured during steady swimming at 1.2 lengths s(-1) in a flow tank. Despite very similar morphology among the individual finlets, there was considerable variability in finlet flexure during a stroke. Several of the finlets were relatively rigid and flat (with intrafinlet angles close to 180 degrees during the stroke), although intrafinlet angle of the proximal portion of the most posterior finlet varied considerably over the stroke and was as low as 140 degrees midstroke. Finlets showed complex orientations in three-dimensional space over a stroke, and these orientations differed among the finlets. For example, during tail deceleration the proximal portion of the fifth finlet achieves a mean angle of approximately 75 degrees with the xz plane, while the distal portion of this finlet is oriented at 110 degrees. Our data suggest that the trajectory of local water flow varies among finlets and that the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by the tail of swimming mackerel.     

Steroidogenic and maturation-inducing potency of native gonadotropic hormones in female chub mackerel, Scomber japonicus

ABSTRACT: BACKGROUND: The gonadotropins (GtHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are produced in the pituitary gland and regulates gametogenesis through production of gonadal steroids. However, respective roles of two GtHs in the teleosts are still incompletely characterized due to technical difficulties in the purification of native GtHs. METHODS: Native FSH and LH were purified from the pituitaries of adult chub mackerel, Scomber japonicus by anion-exchange chromatography and immunoblotting using specific antisera. The steroidogenic potency of the intact chub mackerel FSH (cmFSH) and LH (cmLH) were evaluated in mid- and late-vitellogenic stage follicles by measuring the level of gonadal steroids, estradiol-17beta (Epsilon2) and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P). In addition, we evaluated the maturation-inducing potency of the GtHs on same stage follicles. RESULTS: Both cmFSH and cmLH significantly stimulated E2 production in mid-vitellogenic stage follicles. In contrast, only LH significantly stimulated the production of 17,20beta-P in late-vitellogenic stage follicles. Similarly, cmLH induced final oocyte maturation (FOM) in late-vitellogenic stage follicles. CONCLUSIONS: Present results indicate that both FSH and LH may regulate vitellogenic processes, whereas only LH initiates FOM in chub mackerel.     

Molecular and morphologic approaches to discrimination of variability patterns in chub mackerel, Scomber japonicus

The systematic status and the evolutionary biology of chub mackerel (Scomber japonicus) in the South West Atlantic Ocean is confusing with an unknown degree of genetic differentiation and reproductive isolation between units. Simultaneous genetic and morphologic analyses were made on 227 fish collected from two areas of the South West Atlantic Ocean and one from the Mediterranean Sea. The genetic analysis was based on 36 protein-coding loci, 16 of which were variable. The morphologic analyses include six morphometric length measurements and a meristic character. Correspondence between genetic and morphologic variability patterns indicates isolated Mediterranean and Southwest Atlantic subgroups of S. japonicus and, less clearly, possible additional divergence in two regional stocks within the latter group. The most conservative approach to management is to manage the stocks independently of one another.     

Purification and characterization of a collagenase from the mackerel,Scomber japonicus

Collagenase from the internal organs of a mackerel was purified using acetone precipitation, ion-exchange chromatography on a DEAE-Sephadex A-50, gel filtration chromatography on a Sephadex G-100, ion-exchange chromatography on DEAE-Sephacel, and gel filtration chromatography on a Sephadex G-75 column. The molecular mass of the purified enzyme was estimated to be 14.8 kDa by gel filtration and SDS-PAGE. The purification and yield were 39.5-fold and 0.1% when compared to those in the starting-crude extract. The optimum pH and temperature for the enzyme activity were around pH 7.5 and 55 degrees, respectively. The K(m) and V(max) of the enzyme for collagen Type I were approximately 1.1mM and 2,343 U, respectively. The purified enzyme was strongly inhibited by Hg2+, Zn2+, PMSF, TLCK, and the soybean-trypsin inhibitor.     

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.     

The diet of blue whiting, hake, horse mackerel and mackerel off Portugal

This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast.     

Diet composition of the juvenile chub mackerel (Scomber japonicus) in the Aegean Sea (Izmir Bay, Turkey)

Stomach contents of 296 juvenile chub mackerel (Scomber japonicus Houttuyn, 1782) specimens were examined based on samplings carried out in Izmir Bay (Aegean Sea, Turkey) during 2001. In terms of percentage weight (W%), fishes were the main food during summer and autumn. Thaliaceans (Salpa sp.) constituted the most important food source in winter, whereas planktonic crustaceans (Amphipoda, Copepoda) were the main prey during spring. According to the Bray–Curtis similarity index, diet of the chub mackerel was 64.1% similar during the summer, winter and autumn seasons.     

The physical basis of reflective communication between fish,with special reference to the horse mackerel,Trachurus trachurus

Some properties of reflecting structures in the external surfaces of Trachurus trachurus and some other fish are described. These are related to the hypothesis that such structures are useful, especially to schooling fish, for communicating information on relative positions, orientations, and movements between neighbours. In addition to the silvery layers on the main body surfaces, there are: (a) highly silvered patches on the tail, the pectoral fins and the jaws which, in the sea, will become much brighter or darker with any movement such as a tailbeat or mouth opening which changes their orientations in the ambient lightfield, and (b) structures such as the dorsal lateral line which, in the sea, will only appear bright from certain directions. To us, the colours of the ventral flanks change from bright red to blue with direction orientations and have special reflectivity curves close to those predicted by A.F. Huxley for interference reflectors which are ''ideal'' λ/4 stacks of guanine crystals and cytoplasm. The wavebands best reflected by such platelets move to shorter wavelengths with increasing angle of incidence, also in accord with these equations. At normal incidence, the outer layer of platelets reflects maximally for far-red light which penetrates only a short distance in the sea. Such layers can, however, be useful at oblique angles where they reflect maximally in the yellow and blue. The inner layer of reflectors reflects very strongly in the blue at normal incidence, but reflects in the ultra-violet at oblique angles. Some theoretical studies are made on the ways in which the patterns of reflectivity by single and superposed layers of λ/4 stacks could signal a fish''s movements or its position relative to its neighbours.     

Feeding habits of horse mackerel, Trachurus trachurus (Linneaus, 1758), from the central Adriatic Sea

The feeding habits of the horse mackerel, Trachurus trachurus, from the central Adriatic Sea were investigated with respect to fish size and season. Stomach contents of 1200 specimens 12.9–37.6 cm total length (TL) taken at monthly intervals (January–December 1995) were analyzed. Of the total number of stomachs examined, 597 were empty (49.7%). This percentage varied significantly with season; the maximum number of empty stomachs was observed during January (80%) and February (82%) and a minimum number observed during July (15%) and August (19%). A total of 30 different prey species belonging to five major groups: Crustacea (Euphausiacea, Mysidacea, Decapoda), Cephalopoda, and Teleostei was identified in the stomach contents. Euphausiids were the most important ingested prey in all seasons as well as in small‐ and medium‐size classes (<28 cm TL). Two species of euphausiids, Nyctiphanes couchii (%IRI = 36.0) and Euphausia krohni (%IRI = 12.9), were the most frequent prey. The proportion of teleosts in stomach contents increased with the increasing size class of horse mackerel and was 15.5% IRI in >30 cm TL individuals. The mean weight of stomach contents increased significantly for fish larger than 24.1 cm TL, while the mean number of prey items significantly declined in the large‐size classes.     

Immunoreactivity of gonadotrophs (FSH and LH Cells) and gonadotropin subunit gene expression in the male chub mackerel Scomber japonicus pituitary during the reproductive cycle

The gonadotropins (GtHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are heterodimers composed of a common α subunit (GPα) and a unique β subunit (FSHβ or LHβ); they are synthesized in and secreted from gonadotrophs (FSH and LH cells) in the pituitary. Little is known about the roles of FSH and LH during spermatogenesis in perciform fishes. In this study, we examined immunoreactive changes in FSH and LH cells, and changes in the gene expression of the three gonadotropin subunits in the pituitary of male chub mackerel Scomber japonicus during testicular development. FSHβ-immunoreactive (ir) and LHβ-ir cell area were measured immuno-histochemically based on the FSH and LH cell-occupying area in the proximal pars distalis. The FSHβ-ir cell area increased significantly during spermiation, while FSHβ mRNA levels, already high at the beginning of spermatogenesis, increased further, peaking during spermiation. In contrast, LHβ-ir cell area and LHβ mRNA levels, which were low at the beginning of spermatogenesis, increased significantly during late spermatogenesis, peaking during spermiation. For both FSH and LH, GtHβ-ir cell area and GtHβ mRNA levels decreased until gonadal resting. GPα mRNA levels showed similar changes to LHβ mRNA levels. These results suggest that in the chub mackerel, FSH may play an important role in the early and late phases of spermatogenesis, and that LH may play a role during late spermatogenesis and spermiation. Moreover, our results demonstrate that changes in GtHβ-ir cell area were accompanied by similar changes in the expression of the FSHβ and LHβ genes, both of which increased during testicular development.     

Substrate specificity of chitinases from two species of fish, greenling, Hexagrammos otakii, and common mackerel, Scomber japonicus, and the insect, tobacco hornworm, Manduca sexta

Three chitinase isozymes, HoChiA, HoChiB, and HoChiC, were purified from the stomach of the greenling, Hexagrammos otakii, by ammonium sulfate fractionation, followed by column chromatography on Chitopearl Basic BL-03 and CM-Toyopearl 650S. The molecular masses and pIs of HoChiA, HoChiB, and HoChiC are 62 kDa and pH 5.7, 51 kDa and pH 7.6, and 47 kDa and pH 8.8, respectively. Substrate specificities of these chitinases were compared with those of another fish stomach chitinase from the common mackerel, Scomber japonicus (SjChi), as well as two from the tobacco hornworm, Manduca sexta (MsChi535 and MsChi386). The efficiency parameters, kcat/Km, toward glycolchitin for HoChiA and SjChi were larger than those for HoChiB and HoChiC. The relative activities of HoChiA and SjChi toward various forms of chitin were as follows: shrimp shell or crab shell alpha-chitin > beta-chitin > silkworm cuticle alpha-chitin. On the other hand, the relative activities of HoChiB and HoChiC were beta-chitin > silkworm alpha-chitin > shrimp and crab alpha-chitin. MsChi535 preferred silkworm alpha-chitin to shrimp and crab alpha-chitins, and no activity was observed toward beta-chitin. MsChi386, which lacked the C-terminal linker region and the chitin-binding domain, did not hydrolyze silkworm alpha-chitin. These results demonstrate that fish and insect chitinases possess unique substrate specificities that are correlated with their physiological roles in the digestion of food or cuticle.     

Anisakis simplex larvae: infection status in marine fish and cephalopods purchased from the Cooperative Fish Market in Busan, Korea

The infection status of marine fish and cephalopods with Anisakis simplex third stage larva (L3) was studied over a period of 1 year. A total of 2,537 specimens, which consisted of 40 species of fish and 3 species of cephalopods, were purchased from the Cooperative Fish Market in Busan, Korea, from August 2006 to July 2007. They were examined for A. simplex L3 from the whole body cavity, viscera, and muscles. A. simplex L3 were confirmed by light microscopy. The overall infection rate reached 34.3%, and average 17.1 larvae were parasitized per infected fish. Fish that recorded the highest infection rate was Lophiomus setigerus (100%), followed by Liparis tessellates (90%), Pleurogrammus azonus (90%), and Scomber japonicus (88.7%). The intensity of infection was the highest in Gadus macrocephalus (117.7 larvae per fish), followed by S. japonicus (103.9 larvae) and L. setigerus (54.2 larvae). Although abundance of A. simplex L3 was not seasonal in most of the fish species, 10 of the 16 selected species showed the highest abundance in February and April. A positive correlation between the intensity of L3 infection and the fish length was obvious in S. japonicus and G. macrocephalus. It was likely that A. simplex L3 are more frequently infected during the spring season in some species of fish. Our study revealed that eating raw or undercooked fish or cephalopods could still be a source of human infection with A. simplex L3 in Korea.     

The reproductive biology of the horse mackerel Trachurus trachurs (L.) in the North Sea and English Channel

In the horse mackerel the gametes develop asynchronously and are released in batches. The maturity cycle is characterized by a rapid post-spawning recovery period and a relatively long period of oocyte maturation. Mean gonad weight reached a peak in June and intraovarian hyaline oocytes occurred from May to August. Determination of fecundity was complicated by resorption of oocytes both before and after spawning, and by the fact that resting and developing oocytes were not clearly separated by size. An estimate of'potential fecundity'was obtained by a combination of histology and oocyte measurement. Plankton surveys showed that a major spawning area exists in the Southern Bight of the North Sea, with eggs occurring from May to late August. An estimate of annual egg production was combined with the fecundity data to give an estimate of stock size of about 500 000 tons.     

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).