Kazunari Yano

Reproductive biology of the black dogfish, Centroscyllium fabricii, collected from waters off western Greenland

The reproductive biology of 1124 male (165–760 mm TL) and 1476 female (175–898 mm TL) black dogfish, Centroscyllium fabricii , was examined. The sharks were caught off western Greenland with bottom otter trawls. Size at maturity was about 550 mm TL in males and 650 mm TL in females. Ovarian ova did not continue to develop during gestation. The sex ratio of embryos was 1:1. Litter size ranged from 4 to 40, with a mean of 16–4. The total number of mature ova, fertilized ova, or embryos tended to increase with size of the females. Development of black dogfish embryos is dependent solely on yolk reserves. Near-term embryos (152–192 mm TL) had completely absorbed their external yolk sacs. The smallest free-living specimens collected in this study were 165 mm TL for males and 175 mm TL for females. The black dogfish does not seem to have a well-defined breeding season. This species displayed a well-defined pattern of depth segregation by size. The sex ratios in five shallow depth strata (500–599, 600–699, 700–799,800–899, and 900–999 m) were 1:1, but those of three deeper depth strata (1000–1099,1100–1199, and 1200–1299 m) contained a significantly greater number of females than males. Four abnormal hermaphrodites possessed gonads containing both testicular and ovarian tis-sues. Two specimens had normal female reproductive organs (e.g. ovaries, oviducts, nidamental glands, and uteri) as well as claspers.

Observations of mating behavior of the manta ray,manta birostris, at the ogasawara islands, japan

On 11 July 1997, the mating behavior of wild manta rays,Manta birostris, was observed while skin diving off Chichijima. Ogasawara Islands, Japan, and recorded with 49 underwater photographs and about 20 minutes of video tape. The female manta ray involved was estimated as being approximately 5 m in dise width (DW) and the two males involved, approximately 4 m DW. Copulatory behavior of the two males appeared to be almost the same, copulation itself being of the abdomen-to-abdomen type. Initially, the males chased the female for 20–30 minutes, all animals swimming at approximately 10 km/h. Each copulation event occurred within one meter of the surface, during which time the participating male grasped the tip of the females left pectoral fin with his mouth. The clasper was inserted for 90 seconds (Male No. 1) and 60 seconds (Male No. 2), respectively. The mating behavior sequence of the manta rays involved following five steps. 1.: Male chases behind the tail of the female, attempting (several times) to grasp the latters pectoral fin (chasing behavior). 2.: Male bites the tip of the females pectoral fin, before positioning itself against the latters underside (biting behavior). 3.: Male inserts a clasper into the cloaca of the female (copulating behavior). 4.: Male removes the clasper from the cloaca of the female, but continues biting the latters pectoral fin (post-copulating behavior). 5.: Male releases the pectoral fin of the female, setting her free (separating behavior).

Reproductive biology of the slender smoothhound,Gollum attenuatus, collected from New Zealand waters

SynopsisThe reproductive biology of 385 male and 373 female slender smoothhounds,Gollum attenuatus, collected from New Zealand waters was examined. Size at maturity for both sexes was about 700 mm TL. Litter size was usually two. The sex ratio of embryos was 1:1. The right ovary ovulated 50–100 ova, 4–8 mm in diameter, and 30–80 ova were enclosed in each egg capsule. Only one embryo developed from the many ova in each egg capsule, the other undeveloped ova were ingested and passed to an external yolk sac which formed the yolk supply for the developing embryo.

Observations on the Effect of Visual and Olfactory Ablation on the Swimming Behavior of Migrating Adult Chum Salmon, Oncorhynchus keta

The behavior of chum slamon,Oncorhynchus keta, was studied using ultrasonic telemetry in the waters off the Okhotsk coast of Hokkaido from 1979 to 1981. Thirty-six adult fish were outfitted with a 50 KHz ultrasonic transmitter provided with either a depth sensor, depth/illumination sensors, or depth/ temperature sensors. Twenty-one of the experimental fish were used as controls and left intact. Of the remaining fish, six had their sight destroyed, seven had their olfactory nerves severed or their nares filled with wax, one had both senses destroyed, and one had a sham operation, but had only a shallow transverse cut made in the skin over the olfactory nerves. Control fish and the fish with the sham operation initially swam in a horizontal zigzag pattern while fish with an obliterated sense swam in a similar pattern but to a reduced extent. The horizontal and vertical speeds of the intact fish were faster than those of the fish with a destroyed sense. Amplitude of vertical movements of the intact fish stretched from surface to bottom, while fish with destroyed vision tended towards midwater. Fish without an olfactory sense tended to be at the surface or near the bottom. Regular vertical movement would be effective in refreshing olfactory epithelia which might become acclimated when exposed to one odor. The vertical movements can be found in the horizontal zigzag movements in coastal and near shore migrations, as well as in the stream phase of homing. The zigzag movements, both horizontal and vertical, allow the fish to sense the water masses and locate the correct tributary.

A review of the systematics of the sleeper shark genus Somniosus with redescriptions of Somniosus (Somniosus) antarcticus and Somniosus (Rhinoscymnus) longus (Squaliformes: Somniosidae)

Past treatments of the sleeper shark genus Somniosus generally recognize three species: S. microcephalus, S. pacificus, and S. rostratus. Based on morphometrics and meristics, we conclude that this genus includes two subgenera (Somniosus and Rhinoscymnus) and five species. Subgenus Somniosus differs from Rhinoscymnus by being much larger when adult and in having more numerous tooth rows in the lower jaw, hooklike rather than leaf-shaped dermal denticles, more numerous spiral valve and vertebral counts, and a poorly calcified vertebral column. Subgenus Somniosus includes S. (Somniosus) microcephalus and S. (S.) pacificus of the Northern Hemisphere and S. (S.) antarcticus of the Southern Hemisphere. Although Somniosus antarcticus has been synonymized with S. microcephalus and identified as S. pacificus in past literature, it differs from S. microcephalus in having a shorter interdorsal space, a more posterior first dorsal fin, lower dorsal fins, more numerous tooth rows in the lower jaw, more numerous spiral valve counts, and fewer precaudal vertebrae. Somniosus antarcticus also differs from S. pacificus by having a shorter prebranchial length, lower dorsal fins, more numerous spiral valve counts, and slightly more precaudal vertebrae. Subgenus Rhinoscymnus includes S. (Rhinoscymnus) rostratus from the eastern North Atlantic and Mediterranean Sea (senior synonym of S. bauchotae) and S. (R.) longus from the western Pacific Ocean. Somniosus longus has been synonymized with S. rostratus, but differs in having a relatively longer second dorsal fin, a slightly larger eye, more lower tooth rows, and slightly higher spiral valve counts. Both Somniosus (Somniosus) antarcticus and S. (Rhinoscymnus) longus from the Pacific Ocean were redescribed. A key to the species and the geographical distribution of all species are provided.

Comments on the Reproductive Mode of the False Cat Shark Pseudotriakis microdon

Fifteen specimens of the false cat shark, Pseudotriakis microdon, were collected at depths between 530-990 m around the Okinawa Islands, Japan, and from the Three Kings Ridge off New Zealand. Reproductive systems of immature and mature males and females are described. Three gravid females were captured each with two embryos. The ratio of embryonic males to females was 1:1. The ovary contained numerous ova 2-10 mm in diameter. Yolk material was observed in the uteri and weighed 730-1010 g. The stomachs of two embryos contained yolk material and egg capsules indicating oophagous behavior. Embryos appear to transfer yolk from ingested egg fragments to the external yolk sac for storage. The mode of embryonic nutrition of the false cat shark appears to differ from previously described modes in elasmobranchs and appears to represent a modified form of oophagy in which the yolk reserves of the external yolk sac are replenished and used subsequently in the last stages of gestation. This is the first fully documented report of oophagy in a nonlamniform shark.

Some aspects of the biology of the goblin shark, Mitsukurina owstoni , collected from the Tokyo Submarine Canyon and adjacent waters, Japan

A total of 148 specimens of Mitsukurina owstoni were examined for morphology, distribution, stomach contents, and reproductive condition. Sixty-nine males (81.7–208.5 cm in total length, TL) and 56 females (92.8–196.1 cm TL) were collected with bottom gillnets along a steep slope of the Tokyo Submarine Canyon (100–350 m depth) from May 1995 to October 1996. In addition, data were obtained from 23 specimens of M. owstoni collected from Sagami Bay, Suruga Bay, and the Enshu-nada Sea from 1972 to 2001. Japanese catch records already published (from 1898) plus those in the present study were from the Pacific coast of Japan, from Choshi to the Kii Peninsula. The main fishing season for M. owstoni by bottom gillnet fishing in the Tokyo Submarine Canyon was October to April, at depths of 200–245 m. No specimens examined were sexually mature, including the largest male (208.5 cm TL) and female (196.1 cm TL) recorded. Of 110 stomachs from specimens from the Tokyo Submarine Canyon, 32 (29.1%) were empty. The remainder variously included teleost fishes, squids, decapods, isopods, digested food, and human refuse. Teleost fishes (Macrouridae sp. and Stomiidae spp.), an isopod (Cymothoidae), and decapods (Pasiphaea sinensis and Sergia sp.) were the only identifiable prey, the indication being that teleosts (all size ranges) were of primary importance as prey for M. owstoni.

Comparison of Morphometrics of Atlantic and Pacific Specimens of the False Catshark, Pseudotriakis microdon, with Notes on Stomach Contents

Morphometrics of Atlantic and Pacific specimens of the false catshark, Pseudotriakis, were compared and found to differ little between oceans. Morphometric characters reported to separate Pacific P. acrales from Atlantic P. microdon change allometrically, and P. acrales is confirmed as a junior synonym of P. microdon. Stomachs contained such varied items as sharks, teleost fishes, squids, and octopi

Further description and notes of natural history of the viper dogfish, Trigonognathus kabeyai from the Kumano-nada Sea and the Ogasawara Islands, Japan (Chondrichthyes : Etmopteridae)

The viper dogfish, Trigonognathus kabeyai is further described on the basis of 19 male [176–470 mm in total length (TL)] and 13 female (325–539 mm TL) specimens collected from the Kumano-nada Sea. In addition, the holotype, paratype, and seven specimens collected from the stomachs of Taractichthys steindachneri and Thunnus obseus from the Ogasawara Islands, Japan, were also examined. This is the first description of large (adult) specimens. The allometric size-on-size equation Y = aXb was used to determine morphometric growth patterns, positive allometry, negative allometry, and isometry. Size at maturity was about 430 mm TL for males and about 520 mm TL for females. Myctophid fishes consisting of Diaphus gigas, Diaphus spp., Benthosema fibulatum, and Benthosema sp. were the only identifiable prey in the stomachs of Trigonognathus kabeyai examined. Most of the prey fishes were found almost intact and usually had puncture holes made by teeth. On the basis of stomach content and jaw morphology, this species is thought to be a ram feeder.

The effect of the mesoparasitic barnacle Anelasma on the development of reproductive organs of deep-sea squaloid sharks, Centroscyllium and Etmopterus

Specimens of the mesoparasitic barnacle, Anelasma, were found attached to several host deep-sea squaloid sharks, Centroscyllium fabricii from off Greenland, Etmopterus princeps from the Canary Islands, and Etmopterus unicolor and Etmopterus granulosus from Three Kings Ridge and Louisville Ridge near New Zealand. One to three parasites were partially embedded in each host shark in the head, mouth, bases of 1st and 2nd dorsal fins, pectoral and pelvic fins, caudal fin, abdomen or claspers. Testes and claspers of parasitized mature-sized males were less developed than those of non-parasitized mature males. The ova of parasitized females of mature size were small and whitish-yellow compared to the large yellow ova of non-parasitized mature females. The number of mature ova in a parasitized specimen was lower than expected in relation to a non-parasitized individual of the same size. Attachment of parasitic barnacles appeared to retard the development of reproductive organs of host sharks.