Hiroaki Hashimoto

Two-Dimensional Fermi Liquid Behavior of the Superconductor Sr2RuO4

We report detailed normal state measurements of the resistivity, magnetic susceptibility and specific heat of high-quality single crystals of Sr 2 RuO 4 , the only copper-free, layered perovskite superconductor ( T c ≈1 K). It is intriguing that despite its very strong anisotropy (the ratio of the interlayer to in-plane resistivity exceeds 500) arising from the essentially two-dimensional Fermi surface, the normal state properties are consistent with a universal description for a strongly correlated Fermi liquid. Therefore, Sr 2 RuO 4 serves as an ideal reference material for the investigation of the limits of applicability of Fermi liquid theory to other highly correlated layered compounds, including high- T c cuprates.

Phylogenetic relationship of two Mola sunfishes (Tetraodontiformes: Molidae) occurring around the coast of Japan, with notes on their geographical distribution and morphological characteristics

Phylogenetic analyses were conducted using complete nucleotide sequences of the D-loop in the mitochondrial genome of Mola specimens, collected mainly in Japanese waters, to clarify the genetic features and distribution patterns of Mola sunfishes. Two significantly distinct groups (designated A and B) were present in the genus, with a considerable net nucleotide sequence divergence between the two (8.4%). The two groups occurred sympatrically around the Japanese coast, as previously suggested by Sagara et al. (2005). Group A occurred mostly on the Pacific coast of eastern Japan, while group B was widely distributed along the Kuroshio Current, strongly suggesting different migration routes for each group. The morphological characteristics of the two group specimens were differentiated via the head bump, body proportions and shape of the clavus. Through the addition of Mola sequence data taken from outside Japan to our phylogenetic analyses, three independent groups, including groups A and B, were found, each with a wide geographical distribution, which suggests the presence of at least three independent species within the genus Mola.

Short-term foraging patterns of individual cornetfish, Fistularia commersonii, based on stomach content analysis

Abstract Stomach contents of 75 specimens of the cornetfish Fistularia commersonii, collected in shallow water off Kuchinoerabu-jima Island, southern Japan were analyzed. Many fish contained multiple prey. The prey were mostly fish, grouped into two types, pelagic and reef fishes. The size of prey increased as the size of F. commersonii increased. All the small individuals (<50 cm SL) had fed on only small reef fish. However, most of the large individuals (>50 cm SL) had fed on either prey type. Both pelagic and reef fishes usually occurred simultaneously in shallow water, suggesting that most of the large cornetfish may selectively hunt either type of prey.

Effects of prey density on nocturnal zooplankton predation throughout the ontogeny of juvenile Platax orbicularis (Teleostei: Ephippidae)

Juvenile Platax orbicularis switches foraging tactics from diurnal herbivory to nocturnal zooplanktivory within a day. To examine how juvenile fish actively feed on zooplankton prey during nighttime, a field-recorded video analysis was conducted in the reefs off Kuchierabu-jima Island, southern Japan. Juveniles consistently showed fast and sudden attacks that were accurately directed at individual zooplankton prey, and changed feeding frequencies with different prey densities. A negative relationship was observed between feeding frequency and prey density, with higher feeding frequencies occurring at lower prey concentrations, implying a disturbance effect of clouded zooplankton prey on the juvenile fish. A clear transition from a ram-based to a suction-based feeding mode was observed with fish size, suggesting that changes in the feeding behaviors occur even in juveniles fishes, without drastic morphological changes.

Feeding Habits of Moray Eels (Pisces: Muraenidae) at Kuchierabu-jima

南西諸島の口永良部島の磯水域において、熱帯性ウツボ科魚類14種、タケウツボ Strophidon ui、ワカウツボ Gymnothorax eurostus、クラカケウツボ G. rueppelliae、ゴマウツボ G. flavimarginatus、ニセゴイシウツボ G. melanospilus、サビウツボ G. thyrsoideus、ヘリゴイシウツボ G. fimbriatus、ドクウツボ G. javanicus、ヘリシロウツボ G. albimarginatus、シマアラシウツボ Echidna Polyzona、クモウツボ E. nebulosa、ゼブラウツボ Gymnomuraena zebra、ホシキカイウツボ Uropterygius macrocephalus、モヨウキカイウツボ U. tigrinus と、未同定のウツボ幼魚の胃内容物を調査した。これらは肉食性で、カニ類、エビ類、シャコ類、ヨコエビ類、巻貝類、ウニ類、魚類を摂餌していた。利用する餌の中で最も重要なものは、特に浅い所に生息しているトゲアシガニ Percnon planissimum などのカニ類であった。ウツボ属 Gymnothorax では、大型個体はカニ類と魚類を主に摂餌していた。アラシウツボ属 Echidna は甲殻類、特にカニ順を摂餌していた。ゼブラウツボ属 Gymnomuraena は固い殻を持つカニ類、巻貝類、ウニ類を摂餌していた。小型のウツボ幼魚(<100mmTL)は基本的にはヨコエビ類を摂餌していた。

Feeding behavior of leaf-like juveniles of the round batfish Platax orbicularis (Ephippidae) on reefs of Kuchierabu-jima Island, southern Japan

Feeding behavior of juvenile batfish Platax orbicularis, which presents a mimic state resembling a fallen leaf drifting on the water surface, were surveyed on reefs off Kuchierabu-jima Island, southern Japan. The fish consistently showed drifting swimming patterns on the surface during daylight hours, and fed in a picking–feeding manner on algae covering floating materials or substrates near the water surface. The fish drastically switched to planktivory during the night as they actively hunted free zooplanktonic particles through combined ram and suction feeding manners. Stomach content analysis supported that the fish adopted different feeding tactics, targeting different food items between the two diel periods. Even without an abrupt change of habitat use, due to its mimic state, juveniles of P. orbicularis explore different preys according to their daily activities.

Harem structure and female territoriality in the dwarf hawkfish Cirrhitichthys falco (Cirrhitidae)

We investigated the territoriality and the spatial and mating relationships of the haremic hawkfish, Cirrhitichthys falco, on a reef off Kuchierabu-jima Island in southern Japan. Each individual maintained a territorial home range which was defended against same-sex conspecifics at the boundary of the home range. The territory of each male encompassed the territories of 2–3 females, allowing the male to completely monopolize mating opportunities with those females. Based on our observations, we classified the harem type of C. falco as a territorial female type. Large juveniles maintained independent home ranges outside the female territories. In contrast, small juveniles were allowed to cohabit within the territory of an adult female. Stomach contents analysis revealed that the smallest size class of C. falco fed primarily on copepods. In contrast, all other size classes fed primarily on decapods. Together, these results suggest that female territoriality plays an important role in defending food resources.

Social control of terminal phase transition in primary males of the diandric wrasse, Halichoeres poecilopterus (Pisces: Labridae)

In many diandric fishes, large territorial males with bright body coloration (terminal phase (TP) males) are derived either from initial phase (IP) females that change sex to male or from IP primary males that change color and behavior, but do not change sex. The mechanism controlling the transition of IP primary males into TP males is not well understood. We conducted cohabitation experiments to examine social conditions favoring TP transition by primary males in the diandric wrasse, Halichoeres poecilopterus. IP primary males always started TP-specific sexual behavior in the presence of a smaller subordinate, and subsequently acquired TP body coloration. In contrast, primary males under subordinate conditions often performed female-like sexual behavior. In pairs with similar body sizes, both individuals initiated TP male behavior. The results suggest that TP transition in primary males may be closely related to a dominance relationship (or size order) within social groups, as it is in the case of sex change by females.

Feeding ecology of three tonguefishes, genus Cynoglossus (Cynoglossidae) in the Seto Inland Sea, Japan

Abstract Feeding ecology was compared among the three tonguefishes Cynoglossus abbreviatus, C. joyneri and C. robustus, collected from Seto Inland Sea, Japan, from June 2000 to May 2001. They are benthivores, consuming mainly gammarid amphipods, shrimps, crabs, gastropods, bivalves and ophiuroids. C. abbreviatus consumed greater proportions of ophiuroids whereas C. joyneri and C. robustus ate more amphipods and shrimps. While C. abbreviatus consumed mostly ophiuroids in all size classes, the diets of C. joyneri and C. robustus showed ontogenetic changes in feeding habits; smaller individuals of C. joyneri and C. robustus consumed gammarid amphipods, whereas larger C. joyneri ate shrimps and gastropods, and larger C. robustus fed mainly on gastropods, crabs, bivalves and polychaetes. Cluster analysis based on diet similarities emphasized that the three Cynoglossus species could be categorized on a size-related basis into three feeding groups: smaller C. joyneri and C. rubustus (<25 cm TL) could be classified as group A, and the larger of them (>25 cm TL) as group B, whereas C. abbreviatus was categorized as group C. This means that some degree of resource partitioning can occur among the three Cynoglossus species. The seasonal changes in the diets were also significant for the three Cynoglossus species.

Foraging behavior and diet composition of Trimma caudomaculata and Trimma caesiura (Gobiidae) on coral reefs in Okinawa, Japan

The feeding habits of two small gobies, Trimma caudomaculata and T. caesiura, were surveyed on coral reefs in Okinawa, Japan. Both species actively exhibited foraging attempts beneath overhanging reef structures during the daytime, and fed on small animals, mainly copepods. Trimma caudomaculata formed feeding schools in water columns to swallow mainly Calanoida and Harpacticoida. Trimma caesiura stayed by themselves on the reef substratum and captured mainly Harpacticoida by taking short jumps into the water column. Diet compositions of these congeneric gobies may reflect differences in their foraging behaviors and use of microhabitats.