Features of the reproductive cycle in females of the beaked redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Sebastidae)

The reproductive status of some categories of females of the beaked redfish Sebastes mentella has been determined as a result of the histological analysis. The histological characteristic of gonads of large nonreproductive females of redfish is presented for the first time. Gonads of mature females that skip spawning are studied. The cytomorphological characteristic of ovaries after larvae extrusion is specified. A broadened maturity scale for gonads of females of S. mentella supplemented with stages that characterize fish that skip spawning and large nonreproductive females is proposed.     

Morphological differences among three color morphotypes of Sebastes inermis (Scorpaenidae)

 Morphological differences among three color morphotypes occurring almost sympatrically (A, reddish type; B, blackish type; C, brownish type) of Sebastes inermis are clarified. Twenty-six morphometric characters and seven meristic characters were examined on about 20 specimens of each morphotype, 15 of the morphometric characters differing significantly. Principal component analysis (PCA) of the morphometric characters showed morphotype C to differ from the other two morphotypes. Canonical discriminant analysis (CDA) of the morphometric characters showed clear separation of each morphotype. Four meristic characters also differed significantly. Modes of pectoral fin ray counts of morphotypes A, B, and C were 15, 16, and 17, respectively, and the modes of anal fin ray counts of morphotypes B and C were 7 and 8, respectively. Many individuals of morphotype A had seven or eight anal fin rays. These differences suggested that the three morphotypes may be reproductively isolated from each other. Received: October 15, 2001 / Revised: March 14, 2002 / Accepted: April 9, 2002     

A new species of Curimatopsis Steindachner (Characiformes: Curimatidae) from the Rio Nhamundá, Amazon basin

A new species of Curimatopsis is described from the Rio Nhamundá, Amazon basin in northern Brazil. The new species is distinguished from congeners by the presence of a distinctive concentration of dark pigmentation over the entire lower lobe of the caudal fin, reticulate pattern of body pigmentation, lower jaw longer than and overlapping the anterior portion of the upper jaw, crescent‐shaped posterior nostril and by morphometric and meristic data. Comments on the phylogenetic position of the new species within Curimatopsis are also provided.     

Phylogenetic relationships among North Atlantic redfish (genus Sebastes) as revealed by mitochondrial DNA sequence analyses

Species structure and phylogenetic relationships among the four currently recognised North Atlantic redfish species, Sebastes mentella (‘deep‐sea’ and ‘oceanic’ phenotype), S. marinus (including ‘giant’ phenotype), S. fasciatus and S. viviparus, were investigated by sequencing the complete mitochondrial NADH dehydrogenase subunit 3 (ND3) gene for 313 individuals (333 including outliers). Low levels of sequence divergence of 0.3–2.3% between the North Atlantic Sebastes haplotypes, low resolution in phylogenetic trees and a star‐like statistical parsimony network indicate a population bottleneck and/or founder event with a subsequent population expansion and a rapid speciation in North Atlantic Sebastes. Diagnostic mutations within the ND3 gene were recognised for some of the species. The results lead to the hypothesis that the ancestral haplotype lineage is now very rare or has suffered extinction and that the most basal lineage is found in S. viviparus. The results further indicate direct descendants in the S. fasciatus and S. marinus lineages from the S. mentella lineage, whereas the S. viviparus lineage originates from an earlier division. The observation of two haplotype lineages in S. marinus with a relatively high level of intraspecific genetic divergence, points towards a possible cryptic speciation.     

Genomic characterization of sex‐identification markers in Sebastes carnatus and Sebastes chrysomelas rockfishes

Fish have evolved a variety of sex‐determining (SD) systems including male heterogamy (XY), female heterogamy (ZW) and environmental SD. Little is known about SD mechanisms of Sebastes rockfishes, a highly speciose genus of importance to evolutionary and conservation biology. Here, we characterize the sex determination system in the sympatrically distributed sister species Sebastes chrysomelas and Sebastes carnatus. To identify sex‐specific genotypic markers, double digest restriction site – associated DNA sequencing (ddRAD‐seq) of genomic DNA from 40 sexed individuals of both species was performed. Loci were filtered for presence in all of the individuals of one sex, absence in the other sex and no heterozygosity. Of the 74 965 loci present in all males, 33 male‐specific loci met the criteria in at least one species and 17 in both. Conversely, no female‐specific loci were detected, together providing evidence of an XY sex determination system in both species. When aligned to a draft reference genome from Sebastes aleutianus, 26 sex‐specific loci were interspersed among 1168 loci that were identical between sexes. The nascent Y chromosome averaged 5% divergence from the X chromosome and mapped to reference Sebastes genome scaffolds totalling 6.9Mbp in length. These scaffolds aligned to a single chromosome in three model fish genomes. Read coverage differences were also detected between sex‐specific and autosomal loci. A PCR‐RFLP assay validated the bioinformatic results and correctly identified sex of five additional individuals of known sex. A sex‐determining gene in other teleosts gonadal soma‐derived factor (gsdf) was present in the model fish chromosomes that spanned our sex‐specific markers.     

Discrimination of the redfish (Sebastes mentella) stock components in the Irminger Sea and adjacent waters based on meristics,morphometry and biological characteristics

Redfish Sebastes mentella samples were collected in 2004 and 2005 during commercial cruises to the Irminger Sea on board the Polish vessel M/T ‘Wiesbaden’. Ichthyological studies included length and weight measurements, sex, gonad maturity stages and age determinations. Meristic and morphometric measurements were performed on digital images of the redfish. Comparison of the pelagic redfish from the northeastern (depths deeper than 500 m) and southwestern (depths shallower than 500 m) fishing grounds of the Irminger Sea indicates a number of differences including spatial and vertical distribution, ambient temperature, length and age composition. Moreover, 12 morphometric and 4 meristic characters differed significantly between fish samples from these two areas. Results of Cluster Analysis showed the clear grouping of samples into that of the ‘oceanic’ component (depth 300–450 m) and the ‘deep sea’ component (depth 550–800 m). These results were confirmed by Principal Component Analysis, which revealed the separation of samples into two catch depth groups. The share of fish allocated by Discriminant Analysis into the pelagic ‘deep sea’ component in the northeastern area was nearly 92%, while the ‘oceanic’ component was dominant in the southwestern area and comprised more than 88% of the fish. Cluster and Principal Component analyses suggest that the ‘oceanic’ component is a more homogeneous group than the ‘deep sea’ component. These results support the management units recently established by ICES.     

Recruitment of stock of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes,Scorpaenidae) in the pelagial of the Irminger Sea and adjacent waters

Results of comparative analysis of several ecologo-populational characteristics and fauna of parasites of deepwater redfish Sebastes mentella from the pelagial of the Irminger Sea and slopes of Greenland are provided. It was established that the nursery area of the species in this part of the northern Atlantic is located in the shelf and shallow-water sites of the Greenland slopes. Near the nursery area, at deepwater sites of the Greenland slope, aggregations of mainly immature specimens (68–86%) with an average length of 35–38 cm are located, and, in the oceanic pelagial, there are mainly mature specimens (91–95%) with a length of more than 30 cm. Considerable similarity and specific features of fauna of parasites of S. mentella from the southeastern slope of Greenland and the pelagial of the Irminger Sea indicate the belonging of fish aggregations in these areas to a single intraspecies group and the migration of maturing specimens from the slope to the pelagial. A conclusion is made that the aggregations of S. mentella in the pelagial of the Irminger and Labrador seas represent a pelagic ecological group formed by rapidly maturing specimens; a near-bottom ecological group at deepwater sites of the slope of Greenland is formed by slowly maturing specimens. No mass migration of the redfish from deepwater areas to shallow sites of the slope and to the oceanic pelagial of the northern Atlantic was recorded.     

Comparative study on the surface ultrastructures of fertilized eggs of three Sebastes species

Fertilized eggs of Sebastes schlegelii, Sebastes pachycephalus and Sebastes hubbsi are morphologically similar under stereomicroscope. However, under the scanning electron microscope, significant differences in the ultrastructures of the egg surface among the three species were observed, and herein, a taxonomic key was proposed for future applications. A clustering analysis based on the ultrastructures of the egg surface and the diameter of the oil globule suggested that among the three species, S. hubbsi and S. pachycephalus were more genetically similar, while S. schlegelii had diverged earlier. The results agree with the conclusions drawn from morphological and molecular analyses on adult samples of the same species.     

Geometric morphometrics reveals body shape differences between sympatric redfish Sebastes mentella, Sebastes fasdatus and their hybrids in the Gulf of St Lawrence

Significant body shape differences were observed between two commercially important redfish species Sebastes fasdatus and Sebastes mentella , in the Gulf of St Lawrence, first classified according to the variability at the MDH-A* locus, a diagnostic criterion for the two species in allopatry. The observed sexual dimorphism was probably related to the presence of gravid females in the sample. Sebastes mentella appeared to be more fusiform than S. fasdatus , a characteristic that may reflect the more pelagic behaviour of S. mentella . The body shape of their hybrids was closer to that of S. mentella . Similarities between hybrids and S. mentella were also observed for meristic characteristics and depth distribution. The implications of these similarities for introgression are discussed. Body shape variability of specimens of hybrid origin was greater than that of either parental species, with features ranging from S. mentella-like to S. fasciatus -like. The role of introgression in generating morphological variability is emphasized.     

Review of the population structure and ecology of S. mentella in the Irminger sea and adjacent waters

Significant controversies exist over the three types of Sebastes mentella found in the Irminger Sea and adjacent waters. Preliminary genetic studies have given evidence for the existence of three distinct groups, characterized using several molecular genetic markers. The biological or ecological significance of these between-group differences has, however, not been evaluated. In the present paper, we review the life cycle of S. mentella in this area, based on published data. Spawning of S. mentella in the Irminger Sea takes place in a single area above Reykjanes Ridge. The larvae drift towards East Greenland from where they are carried to West Greenland (NAFO Subareas 0+1). Later they return to East Greenland where the main nursery area has been identified. There is evidence for a migration of juvenile fish from the nursery area into the open Irminger Sea, where many different cohorts spawn. We also compare these ecological data with the genetic results and we conclude that the observed genetic differences can be derived from possible genetic drift, selection or mostly from temporal variation (age dependency). which has also been reported for other species with as high longevity as S. mentella. We conclude that S. mentella in the Irminger Sea and adjacent waters comprises one single population.     

The early life history of kurosoi,Sebastes schlegeli (Scorpaenidae), in the Sea of Japan

Larval and juvenile stages of kurosoi,Sebastes schlegeli, are described and illustrated from wild specimens. Some ecological aspects of larvae and juveniles are also described. Notochord flexion occurred between 5.6–7.5 mm SL. Transformation occurred between 13–20 mm SL. Preflexion and flexion larvae ofS. schlegeli can be distinguished from similar larvae by the pigmentation of the dorsal and ventral midlines of the tail and absence of pigmentation on the ventral portion of the rectum. After notochord flexion, the dorsal and lateral regions in both larvae and pelagic juveniles were heavily pigmented, suggesting adaptation for neustonic life style. Larvae and juveniles were caught at many coastal stations, but did not occur in cooler offshore waters. Larvae smaller than 20 mm SL inhabited surface waters. Until ca. 40 mm SL, juveniles inhabited mainly surface waters (without drifting seaweed), but also used other habitats, such as the drifting seaweed, and near the sea bed. Small larvae (<7 mm SL) fed mainly on copepod nauplii. Larger larvae fed on calanoid copepodites andEvadne nordmanni. Pelagic juveniles fed mainly on fish eggs, with fish larvae also being important food items for some individuals. Most food items taken by juveniles that were associated with drifting seaweed were eggs with attaching filaments (Cololabis saira andHyporhamphus sajori), suggesting that the high density of such food items both attracts and keeps juveniles around drifting seaweed.     

Early life history of mebaru,sebastes inermis (scorpaenidae), in sendai bay, japan

The early life history of the viviparous scorpaenid,Sebastes inermis, in Sendai Bay, Japan, was studied and early development described. Newborn preflexion larvae ofS. inermis were about 5.2 mm BL. Notochord flexion occurred at 5.4–8.0 mm BL and transformation at 14–20 mm BL. Preflexion and flexion larvae ofS. inermis were distinguished from similar larvae by the pigmentation pattern along the dorsal and ventral midlines of the tail. Pigmentation inS. inermis was light throughout the larval and early juvenile periods. Planktonic larvae were particularly abundant in coastal waters of Sendai Bay but not offshore. Vertical and horizontal larval sampling indicated that early larvae occupied near surface waters and horizontal larval sampling indicated that early larvae shift to a benthic habitat occurred at about 12 mm BL, at the end of the postflexion larval period.Sebastes inermis do not have a distinct pelagic juvenile stage, unlike many North Pacific species ofSebastes.     

Structure and specific features of formation of aggregations of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) in the Norwegian Sea pelagial

Results of studies of the structure and specific features of formation of aggregations of deepwater redfish Sebastes mentella in the Norwegian Sea pelagial are provided. Data on the biological characteristics of S. mentella from different regions of the Norwegian Sea pelagial do not allow us to consider its aggregations as separate populations. On the basis of comparative analysis of the structure of aggregations in the Norwegian Sea and of population parameters and specific features of the life cycle of S. mentella in different parts of the Atlantic Ocean, its complex intraspecies organization at sites of overlapping of two largest populations—North Atlantic and Norwegian-Barents Sea-was established. The formation of pelagic aggregations in the water area of the Norwegian Sea occurs due to migration of maturing and mature individuals from the adjoining water areas. In the southern areas of the Norwegian Sea, dominant recruitment comes from the pelagial of the northeastern part of the Irminger Sea, which is promoted by the direction of streams of the North-Atlantic Current; it is not excluded either that fish can migrate to the southern part of the sea from the slopes of the Faeroes, Faeroes-Icelandic threshold, and the western coast of Norway. Migration to the northern areas of the sea is mainly performed by rapidly maturing fish from the rearing region from the western slopes of the Barents Sea and Spitsbergen Archipelago. The presence of seasonal migrations hinders the formation in the pelagial of perch isolated groups and promotes their migration.     

Biological and ecological characteristics of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) at different depths in the pelagial of the Irminger Sea

Results of comparative analysis of several ecological and biological indices of Sebastes mentella from the northern Atlantic (the Irminger Sea, Reykjanes Ridge) inhabiting different depths, 0–500 and 501–1000 m, are provided. A considerable similarity in the rates of linear and weight growth, sexual maturation, composition of parasitofauna, the degree of invasion by parasites of most species, specific features of invasion by copepod Sphyrion lumpi, as well as the pattern of pigment formations on the skin of S. mentella from two studied layers, testify to the absence of isolated groups of this species in the pelagial of the Irminger Sea. It was established that the formation of perch aggregations at a depth larger than 500 m takes place due to a partial redistribution from the upper layer of individuals aged 5 to 18 years and a complete departure to large depths of perch individuals older than 18 years. A conclusion was made that it is incorrect to use as a criterion for the intraspecies differentiation of the perch the insignificant differences in the occurrence of pigment formations on the skin that are the result of age changes in fish and an obvious pathology of this phenomenon. A decrease in the occurrence of melanin inclusions in the muscular tissue of fish at a depth larger than 500 m is also related to age changes and the change in the diet of the perch. Vertical variation, in particular biological parameters in pelagic aggregations, was determined by specific features of biology, ecology, and the life cycle of the species. In establishing measures of control of the international fishery in the pelagial of the Irminger Sea, it is necessary to proceed from the unity of aggregations of S. mentella throughout the vertical of their distribution.     

The distribution and specific features of the biology of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) during mating in the pelagial of the northern Atlantic

Data on the spatial-bathymetric distribution, size and age composition, sex ratio, and feeding of deepwater redfish Sebastes mentella in the pelagial of the northern Atlantic (Irminger and Labrador seas) during mating are provided. From 1982 to 1999, the mating of S. mentella took place in the central and southern parts of the Irminger Sea (56°–62° N, 30°–43° W); since 2000 it took place in two geographically isolated areas: in the water area of the open part of the Labrador Sea, at sites of the south of the Irminger Sea adjacent to it (54°–58° N, 38°–50° W), and above the western slopes of the Reykjanes Ridge (62°–65° N, 25°–34° W). It is assumed that during mating in the northern area mixed aggregations of two ecological groups of S. mentella—an oceanic group that distributes in the pelagial and a bottom group that inhabits the slopes of Iceland—are formed. The formation of isolated areas of mating of the species is determined by the orientation of feeding migrations that are simultaneously migrations to spawning grounds. Fish of medium sizes migrate to spawning grounds in the southwestern direction, while large fish migrate in the northern direction; the fertilization of females in these areas occurs at the end of summer. In S. mentella, the seasonal and age differences in food composition are clearly pronounced. With the onset of mating, the males’ intensity of feeding in both regions decreases by a factor of 1.5–2.0, while females continue to feed actively.     

Larval development of the freshwater croaker Pachypops fourcroi (La Cépède 1802) (Perciformes: Sciaenidae)

The larval development of Pachypops fourcroi from the lower Amazon River was described through morphological, meristic and morphometric features. Sixty-five larvae were examined and present a moderate body, slightly elliptical eyes and head ranging from moderate to large. The mouth is initially terminal and becomes subterminal throughout development with three barbels in the mentonian region. The larvae of P. fourcroi can be differentiated from other Sciaenidae in the Amazon basin by the pigmentation pattern, the presence of barbels, head depth, body depth and diameter, and shape of the eye.     

Ecologal and parasitological chracteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes: Sebastidae) from the Norwegian Sea and adjacent waters

Special traits of ecology, zoogeography, formation of fauna of parasites, and occurrence of external lesions are investigated in redfish Sebastes mentella from the Norwegian Sea and the adjacent area of the Barents Sea. A considerable weakening of connection with bottom biocenoses in redfish in the pelagial of the Norwegian Sea indicates that it lives here for most of its annual life cycle. In redfish from south of the open part of the Norwegian Sea, there are noticeable differences in the fauna of parasites and in occurrence of external lesions from those in the fish from the north and east of this sea while traits characteristic of redfish from the Irminger Sea are present.     

Extensive hybridization and associated geographic trends between two rockfishes Sebastes vulpes and S. zonatus (Teleostei: Scorpaeniformes: Sebastidae)

Interspecific hybridization is an important evolutionary process, which has significant influence on the diversity within and between participating taxa. Although interspecific hybridization in terrestrial and freshwater organisms has been subjected to many detailed studies, studies in marine realm have been limited in terms of both numbers and detail. In this study, the potential for interspecific hybridization between two rockfishes, Sebastes vulpes and S. zonatus, occurring in the western North Pacific, was assessed on the basis of 177 specimens collected from three sampling localities within the main geographic distribution of both species, and analysed using a combination of amplified fragment length polymorphisms (AFLP), mitochondrial DNA (mtDNA) markers and morphometric characters. Bayesian‐based individual genetic assignment based on 364 AFLP loci detected a total of 63 (35.6%) hybrid specimens in the data set, the presence of interspecific hybrids also being rigorously supported by mtDNA analysis using partial sequences from the control region and morphological analysis based on 31 morphometric characters. Hybrids from all three localities were found, showing a common pattern of biased introgression across the localities whereby hybrids were more closely related to S. zonatus than to S. vulpes. Apart from this common pattern, rates of hybridization varied considerably among the localities, being greater in the northern localities. Variations in the local rates of hybridization were associated with variations in habitat segregation and thermal regime, implying that vertical water temperature regimes determined the extent of habitat segregation of the two species and, accordingly, the opportunity for hybridization.     

Habitat characteristics of juvenile cowcod, <Emphasis Type="Italic">Sebastes levis</Emphasis> (Scorpaenidae), in Southern California

We characterized habitat requirements of juvenile cowcod, Sebastes levis, using information from surveys conducted aboard the manned research submersible Delta. We conducted 303 dive surveys on rocky banks and outcrops in water depths between 28 and 365 m in southern and central California, covering 483 km (963,940 m²) of seafloor. We counted 549,263 fishes from at least 134 species; 216 individuals were juvenile cowcod, S. levis, of 45 cm or less in total length (TL). Juvenile cowcod occupied depths between 52 and 330 m and demonstrated ontogenetic shifts in their habitat associations. Small fish (5–20 cm TL) lived primarily among cobbles or cobbles and small boulders. As fish grew, they moved into high-relief rock habitats, including boulder fields and rock ridges. Small cowcods were found with pygmy, Sebastes wilsoni, and swordspine, Sebastes ensifer, rockfishes. Larger juveniles often associated with juvenile bocaccio, Sebastes paucispinis, juvenile widow rockfish, Sebastes entomelas, and squarespot rockfish, Sebastes hopkinsi. Our study resulted in a characterization of seafloor habitats on a small spatial scale that is relevant to juvenile cowcod nursery areas, which is important when considering effective management strategies for this overfished species.