Squalus Mitsukurii Research Articles

First report of plastic and non-plastic microparticles in stomach of slandertail lanternshark and shortspine spurdog from the edge of East China Sea

This study investigates the presence of plastic and non-plastic microparticles in the gastrointestinal tracts of two deep-sea sharks, Etmopterus molleri (n = 118) and Squalus mitsukurii (n = 6), bycatch from the East China Sea continental shelf. We found a total of 117 microparticles, predominantly fibres (67.52 %), with blue (31.62 %) and black (23.94 %) being the most prevalent colours. E. molleri contained 70 microparticles (0.63 ± 0.93 items/shark), 61.42 % non-plastics like viscose and cotton, while plastics included polyethylene, polyethylene terephthalate, and acrylic. Despite S. mitsukurii's limited sample size, the results show that it takes in a lot of microparticles (47 microparticles, 7.83 ± 2.64 items/shark), 57.44 % non-plastics (viscose, cotton, and ethyl cellulose), and 42.56 % plastics. A positive correlation between microparticle presence and total length was observed for E. molleri. These results provide initial data on microparticle ingestion by these species, highlighting potential ecological risks and trophic transfer implications in deep-sea ecosystems.

A new record of Squalus montalbani (Chondrichthyes: Squaliformes: Squalidae) from the Nansha (Spratly) Islands, South China Sea

The Indonesian greeneye spurdog (or a dogfish shark), Squalus montalbani Whitley, 1931, is widely distributed in the warm temperate to tropical waters of Indonesia, Philippines, the island of Taiwan, and Australia. Previous studies suggested that the distribution of dogfish shark species in the South China Sea is composed of two species, Squalus mitsukurii Jordan et Snyder, 1903 and Squalus brevirostris Tanaka, 1917. In March 2020 a dogfish shark specimen was collected from the Nansha (Spratly) Islands, South China Sea. We identified it as S. montalbani based on morphology and mitochondrial DNA barcoding. Our results confirmed the presence of S. montalbani in the South China Sea, leading us to conclude that it represents a new species record of the genus Squalus in the region. Furthermore, our findings demonstrate that the combined approach is highly effective in identifying Squalus species that share similar morphological characteristics.

Squalus shiraii sp. nov. (Squaliformes, Squalidae), a new species of dogfish shark from Japan with regional nominal species revisited

A new species of deep-water dogfish shark, Squalus shiraiisp. nov., is described herein as endemic to the tropical waters off Southern Japan. This species has been largely misidentified with S. mitsukurii. However, morphological, meristic and morphometric evidence support it to be a separate and undescribed species. Squalus shiraiisp. nov. differs from this species by having body brown in colour dorsally, caudal fin with ventral and dorsal tips markedly tapered and broadly white, dermal denticles uniscuspidate and lanceolate and larger number of precaudal (91–94) and total vertebrae (120–123) (vs. body dark grey to black; caudal fin with ventral and dorsal tips rounded and not white in colour; denticles tricuspidate and rhomboid; 86–90 precaudal and 116–117 total vertebrae). Squalus shiraiisp. nov. is also clearly separated from other Japanese congeners which are herein revisited to include six species, based on the examination of over 150 specimens caught from Japanese waters that were available in ichthyological collections: S. mitsukurii, S. japonicus, S. acutirostris, S. brevirostris and S. suckleyi. Squalus mitsukurii, S. japonicus and S. brevirostris are re-described in detail and the neotype of S. japonicus is herein designated. Squalus acutirostris is treated as a valid species with occurrences in Japan, China and Taiwan and, thus, a provisional diagnosis is given, as well as an updated diagnosis of S. suckleyi. A key to Squalus species from the North-western Pacific Ocean is given and main morphological differences between S. shiraiisp. nov. and the closest related species are discussed.

Re-evaluation of deep-sea dogfishes (genus Squalus) in Japan using phylogenetic inference

Japan is known for its marine biodiversity and diverse ecosystem due to its unique geological composition and water currents creating suitable habitats for a wider range of marine species. A rich deep-sea shark community with high endemism occurs on the continental shelf. Yet, the deep-sea shark taxonomy is still under development and poorly documented.Here, a DNA barcoding technique was adopted using the mitochondrial cytochrome oxidase I (COI) and NADH2 genes of samples collected from Japan with additional samples from genetic databases to draft out a phylogenetic tree of the deep-sea shark genus Squalus (dogfishes). The morphological divergence of congeners was further examined. Bayesian and maximum-likelihood-based species-level phylogenetic analyses of mitochondrial COI, ND2 and combined sequences provided strong support for distinct clades corresponding to the parental species with substantial sequence divergence between parental species. The combined dataset of the COI and ND2 gene was most suitable for barcoding of Squalus dogfishes. A multivariate analysis of morphological traits was largely consistent with the genetic data showing small but discrete differences in phenotypic characteristics allowing to separate Squalus species.Genetic samples of the taxonomically problematic Shortspine spurdog ‘Squalus mitsukurii’ from the Atlantic Ocean and Taiwan did not match with the type material of S. mitsukurii Jordan & Snyder, 1903 from mainland Japan. Squalus mitsukurii once considered a globally distributed species is a single, unique spurdog restricted to temperate Japan and Korea and may present an endemic in the Northwestern Pacific. This study further resolved two genetically and phenotypically distinct species of Squalus dogfishes in Japan, one in sympatry with S. mitsukurii in mainland Japan and one in sympatry with subtropical waters associated congeners in the Ryukyu Archipelago. The occurrence of populations of the ‘high-fin’ Taiwan spurdog, Squalus formosus, in subtropical Japan is herein confirmed.

Description of a new deep-water dogfish shark from Hawaii, with comments on the Squalusmitsukurii species complex in the West Pacific.

Dogfish sharks of the genus Squalus are small, deep-water sharks with a slow rate of molecular evolution that has led to their designation as a series of species complexes, with low between-species diversity relative to other taxa. The largest of these complexes is named for the Shortspine spurdog (Squalusmitsukurii Jordan & Snyder), a medium-sized dogfish shark common to warm upper slope and seamount habitats, with a putative circumglobal distribution that has come under investigation recently due to geographic variation in morphology and genetic diversity. The Hawaiian population of Squalusmitsukurii was examined using both morphological and molecular analyses, putting this group in an evolutionary context with animals from the type population in Japan and closely-related congeners. External morphology differs significantly between the Hawaiian and Japanese S.mitsukurii, especially in dorsal fin size and relative interdorsal length, and molecular analysis of 1,311 base pairs of the mitochondrial genes ND2 and COI show significant, species-level divergence on par with other taxonomic studies of this genus. The dogfish shark in Hawaii represents a new species in the genus, and the name Squalushawaiiensis, the Hawaiian spurdog, is designated after the type location.

Squalus clarkae sp. nov., a new dogfish shark from the Northwest Atlantic and Gulf of Mexico, with comments on the Squalus mitsukurii species complex.

Sharks of the genus Squalus have slow reproductive rates coupled with low genetic diversity, as is typical of deep-water sharks, making this group slow to rebound from depletion due to overfishing. The number of species within Squalus has been expanding recently due to increased attention on taxonomic revision, and a growing research focus on little-known deep-water sharks in general. Here we use genetics and morphology to describe a new species of dogfish shark, Squalus clarkae sp. nov. from the Gulf of Mexico (GoM) which replaces Squalus mitsukurii in this region, and place it in the context of congeners from the Atlantic and elsewhere. Previously, S. clarkae sp. nov. was considered a part of the Squalus mitsukurii species complex, a group of closely related but distinct species. We sequenced the mitochondrial cytochrome oxidase I and the NADH Dehydrogenase II gene of S. mitsukurii from the type location in Japan, S. clarkae sp. nov. from the GoM, as well as three closely related species (S. cubensis, S. blainville, and S. megalops) and S. cf. mitsukurii from Brazil. Squalus clarkae sp. nov. is genetically distinct from other species with significant statistical support (>98.6% bootstrap support/posterior probability), and 2.8% divergent from S. mitsukurii in the type location of Japan. Morphological estimates also revealed differences between S. clarkae sp. nov., S. mitsukurii, and other Atlantic Squalus species, with S. clarkae sp. nov. exhibiting a longer body, smaller interorbital space, shorter caudal fin, and a differently-proportioned first dorsal fin. In general, dogfish sharks in the Atlantic and GoM are characterized by similar but distinct morphology, significant genetic variation, and small species ranges.

Carbonic anhydrase I in a cartilaginous fish, the shortspine spurdog (Squalus mitsukurii)

Carbonic anhydrase (CA), a ubiquitous enzyme found in many species, including fishes, is involved in physiological functions such as pH homeostasis, calcification, photosynthesis, and ionic regulation. CA I, a member of the α-CA family, is a cytoplasmic isozyme involved in carbon dioxide transport, ion exchange, and acid-base balance. Approximately half of the extant shark species occur only in deep waters; however, few published studies on sharks include these taxa. As fisheries worldwide enter deeper waters, the provision of biological data for these little-known taxa is critical to their management and conservation. To address this limitation, we aimed to detect CA I in various tissues of the shortspine spurdog (Squalus mitsukurii) and characterize its physicochemical properties by using sodium dodecyl-sulfate polyacrylamide gel electrophoresis and isoelectric focusing, together with immunohistochemistry. CA I was detected on SDS-PAGE and western blot analysis as a specific band at 29 kDa in various tissues of the shortspine spurdog, and as a specific band at pI 6.5 in various tissues of the shortspine spurdog by IEF and western blot analysis. CA I immunoreactivity in various tissues of the shortspine spurdog was detected in intracellular locations. To our knowledge, this is the first report of the localization of CA isozymes in various tissues of S. mitsukurii.

Bycatch of sharks (Elasmobranchii) in the Patagonian red shrimp Pleoticus muelleri (Bate, 1888) fishery

The double–beam trawl fishery for the Patagonian red shrimp (Pleoticus muelleri) is the main crustacean fishery of the Southwestern Atlantic Ocean. The shark bycatch in 723 tows of this fishery was surveyed from April 2003 to October 2003. Six species of sharks were recorded: Squalus acanthias (n=321); Squalus mitsukurii (n=1); Squatina sp. (n=1); Schroederichthys bivius (n=327); Galeorhinus galeus (n=4) and Mustelus schmitti (n=13). Length-frequency structure, sex composition, spatial distribution and estimation of density and bycatch per unit of effort are given for the main species. The bycatch of sharks in this fishery was estimated in ~61 mt/ year, equivalent to 0.15% of the shrimp total capture in 2003. S. acanthias contributed with 30.5 mt (50.15%) whilst S. bivius contributed with 22.6 mt (37.2%). Whereas the abundance for S. acanthias in Patagonian waters increased by three fold between 1997 and 2001, the abundance of S. bivius in the same period have decreased in the same amount. In addition, losses of important reproductive sites in southern Patagonia for S. bivius were detected. These issues together with the results presented herein add the Patagonian red shrimp fishery to the potential threats S. bivius is exposed to.

Squalus formosus, a new species of spurdog shark (Squaliformes: Squalidae), from the western North Pacific Ocean

A new species of spurdog, Squalus formosus n. sp., from the lower continental shelf and upper continental slope off the coast of Taiwan and southern Japan, is described. It belongs to the 'highfin megalops group', the members of which share a short snout, high dorsal fins, robust dorsal spines, tricuspid denticles and a white posterior caudal margin. Squalus formosus is most similar to Squalus albifrons, a recently described species from eastern Australia, but differs in some morphological characters and fin colouration. Squalus formosus is sympatric with three other species of Squalus in Taiwanese waters, i.e. Squalus brevirostris, Squalus japonicus and Squalus mitsukurii, and can be readily distinguished from these in the following combination of characters: tall and upright first dorsal fin, with a tall and robust spine, short and bluntly pointed snout, white caudal-fin posterior margin and first dorsal fin with a white anterior margin parallel with dorsal spine. This new species was considered by some authors to be conspecific with Squalus blainville from the eastern Atlantic Ocean, but the results of this study reveal that it is probably endemic to Taiwan and southern Japan.

Size Structure, Abundance and Preliminary Information on the Reproductive Parameters of the Shortspine Spurdog (Squalus mitsukurii) in the Argentinean-Uruguayan Common Fishing Zone from the mid-1990s

A total of 1 893 males and 1 124 females of Squalus mitsukurii were collected from latitudes 34o 30' S and 37o 00' S, in the south-western Atlantic Ocean, during early autumn, late autumn and spring 1995, early autumn 1996 and early autumn 1998. Length-frequency distributions significantly varied between sexes for all seasons (P<0.05). Mature males predominated in all seasons throughout the analyzed area, according to their presence in the catches. In all periods sampled, immature females predominated except for late autumn 1995 where mature females were dominant. Significant differences in density among seasons were recorded for immature and mature females and mature males (P<0.05). Density of immature females and mature males were significantly different (P<0.05) for late autumn 1995 and early autumn 1996. Size-at-maturity was 43.1 cm and 55.9 cm total length for males (n = 1 181) and females (n = 862) receptively. The percentage of pregnant females ranged from 21.4% in spring 1995 to 49.8% in late autumn 1995. Ovarian fecundity varied significantly between early autumn 1995 and late autumn 1995 from 1–15 and uterine fecundity from 1–10, respectively. Embryo total length varied from 0.5–22.0 cm, attaining the highest values in autumn months. Sizeat-birth was estimated to be 22–24 cm total length.

Is multiple mating beneficial or unavoidable? Low multiple paternity and genetic diversity in the shortspine spurdog Squalus mitsukurii

Proposed benefits of multiple paternity include increased reproductive output, elevated fitness of progeny, and maintenance of population genetic diversity. However, another consideration is whether multiple paternity is simply an unavoidable byproduct of sexual conflict, with males seek- ing to maximize mating encounters while females seek to minimize the stress of copulation. Here we examined the polyandrous mating system in sharks, with a focus on the reproductive genetics of the shortspine spurdog Squalus mitsukurii. Members of the genus Squalus are long-lived, slow-growing, and employ among the longest gestation periods of any vertebrate. To evaluate multiple paternity and genetic diversity in S. mitsukurii, we genotyped 27 litters plus 96 individuals with 8 microsatel- lite loci. Further, 670 bp of the mtDNA control region were sequenced in 112 individuals to examine population structure. S. mitsukurii in Hawaii showed low genetic diversity relative to other sharks (π = 0.0010 ± 0.0008) and no significant population structure in the Hawaiian Archipelago. Direct allele counts and Bayesian approximations returned concordant estimates of 11% multiple paternity, the lowest observed in sharks to date. Considering the protracted reproductive interval of S. mitsu- kurii, sexual conflict that results from differential male and female reproductive strategies may favor the development of female mating avoidance behavior to minimize trauma. In S. mitsukurii this behavior includes segregation of sexes and an asynchronous reproductive cycle.

A new species of Calicotyle Diesing, 1850 (Monogenea: Monocotylidae) from the shortspine spurdog Squalus mitsukurii Jordan &amp; Snyder and the synonymy of Gymnocalicotyle Nybelin, 1941 with this genus

Calicotyle japonica n. sp., collected from the uterus, rectal gland, archinephric duct and cloaca of the shortspine spurdog Squalus mitsukurii Jordan & Snyder (Squaliformes) off the Pacific coast of Japan, is described. The new species can be distinguished from C. inermis Woolcock, 1936 by the shape of the male copulatory organ; in C. japonica this is directed anteriorly, is sharply bent in the middle and then increases in width toward the tip, whereas it is long, coiled and uniform in width throughout its entire length in C. inermis. Furthermore, the intestinal caeca have many irregular diverticula on both sides and the vaginal apertures are at the level of the common genital pore in C. japonica, whereas in C. inermis the intestine is smooth and the vaginae open at the level of the oötype. A phylogeny constructed using LSU rDNA data indicates that the new species is grouped with other Calicotyle species; based on this, Gymnocalicotyle Nybelin, 1941 is synonymised with Calicotyle Diesing, 1850. Calicotyle is divided into two major clades, with the new species being grouped with Calicotyle species infecting sharks and the second clade consisting of Calicotyle spp. infecting rays. This suggests that the loss of the hamuli in C. japonica and C. inermis, both parasites of sharks, is a comparatively recent event in the evolution of the genus.

Visual optics and ecomorphology of the growing shark eye: a comparison between deep and shallow water species

Elasmobranch fishes utilise their vision as an important source of sensory information, and a range of visual adaptations have been shown to reflect the ecological diversity of this vertebrate group. This study investigates the hypotheses that visual optics can predict differences in habitat and behaviour and that visual optics change with ontogenetic growth of the eye to maintain optical performance. The study examines eye structure, pupillary movement, transmission properties of the ocular media, focal properties of the lens, tapetum structure and variations in optical performance with ontogenetic growth in two elasmobranch species: the carcharhinid sandbar shark, Carcharhinus plumbeus, inhabiting nearshore coastal waters, and the squalid shortspine spurdog, Squalus mitsukurii, inhabiting deeper waters of the continental shelf and slope. The optical properties appear to be well tuned for the visual needs of each species. Eyes continue to grow throughout life, resulting in an ontogenetic shift in the focal ratio of the eye. The eyes of C. plumbeus are optimised for vision under variable light conditions, which change during development as the animal probes new light environments in its search for food and mates. By contrast, the eyes of S. mitsukurii are specifically adapted to enhance retinal illumination within a dim light environment, and the detection of bioluminescent prey may be optimised with the use of lenticular short-wavelength-absorbing filters. Our findings suggest that the light environment strongly influences optical features in this class of vertebrates and that optical properties of the eye may be useful predictors of habitat and behaviour for lesser-known species of this vertebrate group.

Eye growth in sharks: Ecological implications for changes in retinal topography and visual resolution

The visual abilities of sharks show substantial interspecific variability. In addition, sharks may change their habitat and feeding strategy throughout life. As the eyes of sharks continue to grow throughout the animal's lifetime, ontogenetic variability in visual ability may also occur. The topographic analysis of the photoreceptor and ganglion cell distributions can identify visual specializations and assess changes in visual abilities that may occur concurrently with eye growth. This study examines an ontogenetic series of whole-mounted retinas in two elasmobranch species, the sandbar shark, Carcharhinus plumbeus, and the shortspine spurdog, Squalus mitsukurii, to identify regional specializations mediating zones for improved spatial resolution. The study examines retinal morphology and presents data on summation ratios between photoreceptor and ganglion cell layers, anatomically determined peak spatial resolving power, and the angular extent of the visual field. Peak densities of photoreceptors and ganglion cells occur in similar retinal locations. The topographic distribution of neurons in the ganglion cell layer does not differ substantially with eye growth. However, predicted peak spatial resolution increases with eye growth from 4.3 to 8.9 cycles/deg in C. plumbeus and from 5.7 to 7.2 cycles/deg in S. mitsukurii. The topographic distribution of different-sized ganglion cells is also mapped in C. plumbeus, and a population of large ganglion cells (soma area 120-350 microm2) form a narrow horizontal streak across the retinal meridian, while the spatial distribution of ordinary-sized ganglion cells (soma area 30-120 microm2) forms an area in the central retina. Species-specific retinal specializations highlight differences in visually mediated behaviors and foraging strategies between C. plumbeus and S. mitsukurii.

Corrections to ‘Common and Scientific Names of Fishes from the United States, Canada, and Mexico’

Errors in Nelson et al. (2004) that have come to our attention are listed below. Some of these were caught in page proof but not changed in the final publication. Corrections to scientific names follow those given in Eschmeyer (1998, Online). Some minor typographical errors that should not cause confusion are not listed in the table below. For example, we place a comma between the name of the author and the date, as given in examples in the International Code of Zoological Nomenclature, 4 Edition (e.g., Article 22A.2, a recommendation concerning method of citation); however, there is the occasional omission of the comma in the list (e.g., ‘‘Narcine bancroftii (Griffith & Smith 1834)’’ and ‘‘Psenes sio Haedrich 1970’’). Other minor errors are the omission of a space between items in ‘‘Squalus mitsukurii Jordan & Snyder,1903’’, extra space between items in ‘‘Cichlasoma deppii (Heckel, 1840)’’, and omission of comma between items, e.g., ‘‘Atherinidae–En-Old World silversides, Sptinicalos Fr-atherines’’. In the Index, page 283, carpio is listed in error as in Cyprinella, rather than Cyprinus. Apart from the errors corrected here, changes found subsequent to finalizing the 2004 list will be published later. This will include many range extensions of species found in our area, taxonomic changes (e.g., modifications in generic and family limits as well as species status), and new species and higher taxa described since the publication of the sixth edition, along with other changes. Other comments or purported errors came forth from users that resulted from not reading the notes in Appendix 1. Except for the entry ‘‘Elassoma okefenokee’’, we do not give comments here from publications, either those we missed or that appeared subsequent to the sixth edition, that either strengthen decisions made for the 2004 list or that present elaboration of comments. These may be presented in future articles or in the next edition, planned for 2010. Users should note that active taxonomic work often results in differences of opinion on the generic placement of many species (many such differences, when timely communicated for the 2004 list, were mentioned in Appendix 1). Generic allocation of several species are not necessarily changed in the main list to follow the latest taxonomic suggestions when there is reason to believe that these actions are likely to soon change (this has often been done with the advice of specialists of the particular group). The scientific name is intended as a recommendation or guide for the non-taxonomist until more comprehensive revisionary works are completed. We plan to issue regular updates on new species to our area and have Web-site access for these updates. List and explanation of corrections for the main list and Appendix 1. Changes are coded as follows: A 5 authority; C 5 common name; CS 5 change in symbol; D 5 date of name publication; F 5 family; O 5 country of occurrence; PA 5 parentheses added; PD 5 parentheses deleted; S 5 spelling of specific or generic name; + Comment in Appendix 1. Corrected entry listing given here is how we propose to list the taxon in the next (7) edition, except for special notes in brackets ([ ]), planned for publication in 2010 (page numbers here refer to the 6 edition). The changes in common names, however, are deemed to be effective now. Explanation of corrections: Page 189. Euprotomicrus bispinatus. Correction of family placement to Dalatiidae from Etmopteridae. Page 195. Ophichthus frontalis. Parentheses are removed from the author’s name. Page 196. Anchoa exigua. Parentheses were inadvertently omitted from the author’s name; this species was described in Stolephorus. Page 197. Chanos chanos. Change in diacritic mark in spelling of author (Forsskal versus Forsskal). Page 201. Oregonichthys crameri. Formerly recognized as including O. kalawatseti. See O. kalawatseti. Page 206. Noturus baileyi. Common name capitalized as it referred to the Smoky Mountains, from which area the species was described as noted in the 1970 edition. We assume the listing as ‘‘smoky madtom’’ in the 1980 and 1991 editions was an inadvertent error. Page 206. Sciadeops troschelii. Correction of spelling of specific name (from troschellii). Page 206. Sciades hymenorrhinos. Correction of spelling of specific name (from hymenorrhinus). Page 213. Ogilbia ventralis. Parentheses were inadvertently omitted from the author’s name; this species was described in Brosmophycis. Copeia, 2006(3), pp. 559–562

Two new species of hexabothriid monogeneans from the ginzame Chimaera phantasma and shortspine spurdog Squalus mitsukurii

Descriptions are given for two new species of hexabothriid monogeneans, one collected from the gills of shortspine spurdog Squalus mitsukurii and the other from the gills of the ginzame Chimaera phantasma in Sagami Bay on the Pacific coast of Japan. Squalonchocotyle mitsukurii n. sp. from Squalus mitsukurii can be distinguished from Squalonchocotyle squali MacCallum, 1931, the most closely related species, by the inwardly curved vagina. Callorhynchocotyle sagamiensis n. sp. from Chimaera phantasma can be distinguished from all the known species of Callorhynchocotyle Suriano & Incorvaia, 1982 by the structure of the cirrus; in the new species, the cirrus is entirely muscular with a widened opening, while in the four known species it comprises a tubular proximal part and a bulbous distal part.

Maturation of Squalus mitsukurii and Cirrhigaleus asper (Squalidae, Squaliformes) in the southwestern equatorial Atlantic Ocean

Specimens of Squalus mitsukurii (n = 206) and Cirrhigaleus asper (n = 93) were opportunistically collected from the catches of a research vessel using traps and benthic longlines off the coast of northeastern Brazil between March 1997 and August 2002. For both species, larger females than males were captured. Catches of S. mitsukurii were biased toward females (1:4.6), while no significant disequilibrium in sexes was detected for C. asper (1:0.86). Common regressions for total length (TL) and eviscerated weight (EW) were calculated as LnEW = 3.13LnTL-6.217 (S. mitsukurii) and LnEW = 3.22LnTL-7.01 (C. asper). Based on changes to the reproductive tract, females and males of each species were categorized into several stages of maturation. Sizes at sexual maturity for female (n = 169) and male (n = 37) S. mitsukurii were 77.8 and 65.0 cm TL, respectively. Gravid S. mitsukurii had between 3 and 11 embryos that ranged in size from 2.0 to 22.5 cm TL (n = 262). No significant bias in the sex ratio of embryos was detected. A clear relationship between embryonic development and maturation of the ovary demonstrated that female S. mitsukurii are ready to ovulate immediately after parturition. Female (n = 43) and male (n = 50) C. asper approached sexual maturity at 110.0 and 91.0 cm TL, respectively. Uterine fecundity in gravid C. asper ranged from 12 to 19 embryos that varied in size between 4.0 and 21.9 cm TL. Unlike S. mitsukurii, there was no concurrent development of the ovary and embryos. The results are discussed in terms of the reproductive plasticity of S. mitsukurii and the need for further life history studies on both species.

Antidiabetic effect of a new peptide from Squalus mitsukurii liver (S-8300) in streptozocin-induced diabetic mice

We have evaluated the antidiabetic effect of S-8300 (a peptide extracted from shark liver (Squalus mitsukurii)) in streptozocin (streptozotocin)-diabetic mice. Diabetes was induced by a single intravenous injection of streptozocin (150 mg kg(-1)). The effects of S-8300 (3 or 10 mg kg(-1)) on diabetic mice were investigated by observing the changes in the levels of fasting plasma glucose, glycosylated haemoglobin, hepatic glycogen, triglycerides, cholesterol, free fatty acid, superoxide dismutase, and malondialdehyde. Body weight, kidney weight and the degree of injured beta-cells in pancreatic islets were recorded also. Diabetic mice treated with S-8300 showed a significant decrease in the levels of fasting plasma glucose, glycosylated haemoglobin, triglycerides, cholesterol, free fatty acid in plasma and malondialdehyde in tissues. The animals showed a significant increase in the content of hepatic glycogen and the activity of superoxide dismutase. Treatment with S-8300 attenuated the degree of injured beta-cells in the pancreatic islets. The effect of S-8300 was similar to that of glibenclamide (5 mg kg(-1)).

북태평양 중부 해산어장에 있어서 저층 선주낙의 어획실태

This study was conducted to survey the catches of vertical bottom longline fisheries in the sea mount of central northern Pacific(<TEX>$30^{\circ}-42^{\circ}N$</TEX>, <TEX>$170^{\circ}-175^{\circ}E$</TEX>), during the period of July 1 to August 25,2004 by commercial fishing vessel. The number of 57 test fishing was carried out in the central northern Pacific during 43 days and the total catches were 21,092.4kg as 19 fish species, CPUE/day and catches/day were 185 baskets and 490.5kg, respectively. Main fish species caught from the experimental fishing were Squalus mitsukurii (66.3%), Coelorhyrchus asperocephaius (11.7%) and Helicolenus avius (9.8%) and, average inside diameter for fish mouth was 4.0cm over. Catch ratio according to each fishing ground was the order of F, D, J, B and C. Catch ratio fur water depth was the order of 450-500m, 350-400m, 300-350m, 400-450m, 1000-1100m and 500-550m and, main species by water depth was Squalus mitsukurii for 300-400m, Etmopterus lucifer for 300-550m, Coelorhyrchus asperocephaius far 1,000m over. Catch ratio according to the kind of hooks was higher at the hook no.6 for Squalus mitsukurii and no. 5 for Etmopterus lucifer and, catch ratio by baits was higher at squid for Squalus mitsukurii, saury and eel for Helicolemus avius and saury for Etmopterus lucifer. Accordingly, it is thought that the extension of fishing hours is needed with the reduction of damage and loss for fishing gears during fishing operation.

Total Mercury in Muscle Tissue of Five Shark Species from Brazilian Offshore Waters: Effects of Feeding Habit, Sex, and Length

This study was carried out to assess mercury levels in fish from Brazilian offshore waters. Generally sharks have relatively high mercury levels which are also affected by diet, age (associated with length), and sex. Total mercury levels were determined in five shark species with different habits (Carcharhinus signatus, Mustelus canis, Mustelus norrisi, Squalus megalops, and Squalus mitsukurii) which were collected during 1997 in southern Brazil's offshore waters. The highest mercury concentrations, all above the limit established by Brazilian legislation (0.5 μg.g−1), were detected in piscivorous species (C. signatus, S. megalops, and S. mitsukurii) with averages of 1.77±0.56, 1.9±0.58, and 2.22± 0.72 μg.g−1, respectively, while species that feed mainly on invertebrates (M. canis and M. norrisi) had averages of 0.41±0.35 and 0.36±0.28 μg.g−1. These results indicate that feeding habits influence total mercury level in sharks. Methylmercury (as a percentage of total mercury) determined in S. mitsukurii and M. canis also showed an influence of feeding habit. Positive correlations between mercury concentration and length were statistically significant (P<0.05) for all species, except M. norrisi. Although mercury levels were generally higher in males than in females for all species (with the exception of S. mitsukurii), a statistically significant correlation was observed only for M. canis.