From rivers to ocean basins: The role of ocean barriers and philopatry in the genetic structuring of a cosmopolitan coastal predator.

The Bull Shark (Carcharhinus leucas) faces varying levels of exploitation around the world due to its coastal distribution. Information regarding population connectivity is crucial to evaluate its conservation status and local fishing impacts. In this study, we sampled 922 putative Bull Sharks from 19 locations in the first global assessment of population structure of this cosmopolitan species. Using a recently developed DNA-capture approach (DArTcap), samples were genotyped for 3400 nuclear markers. Additionally, full mitochondrial genomes of 384 Indo-Pacific samples were sequenced. Reproductive isolation was found between and across ocean basins (eastern Pacific, western Atlantic, eastern Atlantic, Indo-West Pacific) with distinct island populations in Japan and Fiji. Bull Sharks appear to maintain gene flow using shallow coastal waters as dispersal corridors, whereas large oceanic distances and historical land-bridges act as barriers. Females tend to return to the same area for reproduction, making them more susceptible to local threats and an important focus for management actions. Given these behaviors, the exploitation of Bull Sharks from insular populations, such as Japan and Fiji, may instigate local decline that cannot readily be replenished by immigration, which can in turn affect ecosystem dynamics and functions. These data also supported the development of a genetic panel to ascertain the population of origin, which will be useful in monitoring the trade of fisheries products and assessing population-level impacts of this harvest.

Colour patterns influence symbiosis and competition in the anemonefish-host anemone symbiosis system.

Colour patterns in fish are often used as an important medium for communication. Anemonefish, characterized by specific patterns of white bars, inhabit host anemones and defend the area around an anemone as their territory. The host anemone is used not only by the anemonefish, but also by other fish species that use anemones as temporary shelters. Anemonefish may be able to identify potential competitors by their colour patterns. We first examined the colour patterns of fish using host anemones inhabited by Amphiprion ocellaris as shelter and compared them with the patterns of fish using surrounding scleractinian corals. There were no fish with bars sheltering in host anemones, although many fish with bars were found in surrounding corals. Next, two fish models, one with white bars and the other with white stripes on a black background, were presented to an A. ocellaris colony. The duration of aggressive behaviour towards the bar model was significantly longer than that towards the stripe model. We conclude that differences in aggressive behaviour by the anemonefish possibly select the colour patterns of cohabiting fish. This study indicates that colour patterns may influence not only intraspecific interactions but also interspecific interactions in coral reef ecosystems.

Larval study revealed diversity and life-history traits of crypto-benthic eel gobies.

Because adult and juvenile eel gobies usually hide within the burrows of muddy substrates, their diversity and life history have not yet been fully elucidated. We investigated larval specimens of the eel gobies collected on Okinawa Island in southern Japan. The genus Trypauchenopsis was previously thought to consist of only one species, but our larval collection identified two species, Trypauchenopsis limicola and Trypauchenopsis intermedia, distinguished by their species-specific melanophore arrangements and differences in their fin-ray counts. Taenioides kentalleni were previously known from only two specimens worldwide. A third specimen of this species has now been added from the larval collection. In addition to the three species above, Taenioides gracilis and Caragobius urolepis were identified and the larval morphologies of the five species were described for the first time. All the larvae collected in the present study were at late postflexion stage. T. limicola, T. intermedia and T. gracilis were presumably collected in the estuaries and beaches when approaching their adult habitats at the end of pelagic life. They were 8.5-10.3 mm in standard length, and otolith analysis suggests that their pelagic larval durations are a little longer than 1 month (average 34-37 days). The larval occurrence suggested that the spawning season of T. limicola is May-December, when the water temperature is warmer than approximately 20°C. Our work reveals that studying the larval stage can provide new information on the taxonomy and life history of the elusive cryptobenthic fish.

Age, growth and reproductive biology of a widespread coral reef fish, yellowfin goatfish Mulloidichthys vanicolensis (Valenciennes, 1831).

Yellowfin goatfish Mulloidichthys vanicolensis (Valenciennes, 1831) is a widely distributed commercial fish in the Indo-Pacific. The authors examined the age, growth, sexual maturity and spawning season of M. vanicolensis around Okinawa Island, southwestern Japan, based on sectioned otolith and gonadal histology. Monthly changes in the appearance of an opaque edge indicate the annual formation of otolith bands. This fish shows sexual size dimorphism due to the faster growth and larger size of females compared to males. The von Bertalanffy growth functions were Lt  = 31.0{1 - exp(-0.39(t + 1.62))} for females and Lt  = 28.3{1 - exp(-0.42(t + 1.45))} for males. This species has a short life span, with a maximum age of 7.75 years, and reaches maturity in its first year of life. Observed fork lengths at 50% maturity were 19.4 cm for female and 16.2 cm for male. The main spawning season occurs from May to October. The authors compared their findings with those of previous studies on the life-history characteristics of M. vanicolensis. Spawning season, growth and maturity size differed from those found in previous studies in areas with genetic continuity. Differences in life-history traits between genetically continuous populations suggest a high degree of environmental adaptability for this species, which may be one of the reasons for its widespread distribution.

Large host anemones can be shelters of a diverse assemblage of fish species, not just anemonefish.

The mutualistic relationships between anemonefish (Amphiprion; Pomacentridae) and host sea anemones are well known, but host anemones are also used as shelter by damselfish (Pomacentridae), wrasses (Labridae) and cardinalfish (Apogonidae). The threespot dascyllus Dascyllus trimaculatus (Pomacentridae) is known to live on or near host anemones in their immature phase. Nonetheless, detailed studies on the use of host anemones by other fish species have not yet been conducted. To understand the factors that influence the use of host anemones by other fish species, this study investigated the fish biota around host anemones in the Ryukyu Archipelago. Other than Amphiprion spp. and D. trimaculatus, 10 additional species of fish (9 species of damselfish and 1 species of cardinalfish) were confirmed to temporarily use host anemones as shelter, and five species of wrasse including Labroides dimidiatus came to clean anemonefish. Logistic regression analyses (independent variable: presence or absence of other species of fish; dependent variables: anemonefish aggressiveness, size of host anemone, number of D. trimaculatus) indicated that the size of host anemones is important for the presence of fish, both in species using the anemone as temporary shelter and in cleaner species. Large host anemones can provide shelter and food resources for other species of coral reef fish as well as for anemonefish.

Nighttime migrations and behavioral patterns of Pempheris schwenkii.

BACKGROUND: Although the biomass of the nocturnal fishes is almost same as that of diurnal fishes, most of the ecological studies that examine feeding or reproductive behaviors are on diurnal fishes. Therefore, there is limited ecological information regarding the nocturnal fishes. This fact may be attributed to the difficulty in observing them during darkness. Members of the genus Pempheris (Pempheridae) are one of the most abundant nocturnal fishes on coral reefs. METHODS: The nighttime migrations of Pempheris schwenkii were observed by attaching a chemical luminescent tag. Tagged fishes were followed by an observer without torch and SCUBA, and their positions and estimated depths were plotted on an underwater topographic map. Aquarium tank observation was carried out to further describe their habits during the night. RESULTS: The new tagging method provided good data for observing the migration behavior. In all five observations, the target fishes started nighttime migration from the entrance of their cave within 1 h after sunset. All of them immediately left the inner reef and spent most of the observation time near the surface (0-5 m depth) or shallow (5-15 m depth) water-columns of the outer reef. Their migration pattern varied between days, but they migrated long distance (379-786 m/h) during each observation. The behavior observed in the aquarium tank was categorized into five patterns: schooling, shaking, migrating, spawning, and feeding. Shaking and spawning were observed during one of three observation days. DISCUSSION: The present study firstly clarified the small-scale but dynamic nocturnal migration pattern of P. schwenkii in nature by a new method using chemical luminescent tags. In addition, combined observations from nature and an aquarium could be used to estimate the behavior of this species. Pempheris schwenkii may reduce their predation risk of eggs and adults by spawning at outer reef in nighttime. It was estimated that they can potentially migrate 4-7 km/night. The rapid growth known for this species may have been supported by their feeding behavior where they can fill up their stomach every night with rich zooplankton in outer reefs. Furthermore, the behavior of this species indicates the possibility that they make an important contribution to the flow of energy and materials in their coral reef ecosystem.

Patterns in diversity and species composition in soft-sediment tidepool fishes across topographical types: Implications for conservation with spatial nuances.

Fish communities inhabiting soft-sediment areas are representative conservation targets for coastal habitats, but how the ecological function of soft-sediment tidepools drives diversity is still unknown. To tackle this issue, the ecological functions of soft-sediment tidepools for fishes according to topographic types (open and closed habitats) on Okinawa-jima Island, located in subtropical Japan, were examined in diversity, species composition, and lifestyle (resident and transient species). Landward tidepools serve as permanent habitat for specialists, whereas seaward tidepools are more important for transient species as temporal habitats, which shaped the inverse trend in α- and ß-diversity between topographic types, depending on the habitat heterogeneity and the biological characteristics of resident and transient species. We propose a strategy for the conservation and management of topographically distinct intertidal habitats, basically as a single set, while also considering the ecological functions with spatial nuances at smaller scales within coastal landscapes.

Reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli in the western Pacific Ocean: histological evidence from one of the smallest fishes in the world.

Gobies are generally small fishes which play important roles in estuarine ecosystems, yet little attention has been paid to their life-history traits in the western Pacific region. In the present study, the reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli were explored by examining their populations in a subtropical estuary on Okinawa-jima Island, Japan, over 15 months. The Okinawan populations of both species shared similar reproductive traits. Pandaka trimaculata and P. lidwilli exhibited early female maturation at minimum sizes of 8.8 and 9.4 mm standard length (SL), respectively, which indicate that populations of the Pandaka species in the subtropical region represent some of the smallest fishes in the world. Nonetheless, they also had high relative body sizes at maturity relative to the attained asymptotic SLs, ranging from 75.8% to 80.4%, which suggests that their populations are vulnerable to negative impacts. Both the species also had prolonged spawning periods, extending from February to November (P. trimaculata) and from January to October (P. lidwilli), indicating that these local populations have a high potential for maintenance and resilience. Their spawning periods, sizes at maturity and fecundities varied among seasons and latitudes, possibly because of low water temperatures affecting the relative allocation of energy to growth and reproduction. Such plasticity of life-history traits in these small fishes indicates that they would be suitable models for understanding the evolution of life-history strategies and monitoring the responses of organisms to climate change.

Early development and occurrence patterns of the Pagrinae seabream Argyrops bleekeri (Perciformes: Sparidae): Does early life history have implications for sparid relationships?

The early development and occurrence patterns of Argyrops bleekeri are described based on 87 specimens collected from Nakagusuku Bay on Okinawa Island in southwestern Japan. Larvae and juveniles of the genus Argyrops are distinguished from the other seabreams inhabiting the Western Pacific region by the strength and extent of head spination, body depth, dorsal-fin-ray counts and melanophore patterns. Argyrops bleekeri is easily distinguished from other members of this genus by the presence of a single rudimentary dorsal-fin spine on the first dorsal pterygiophore, melanophore patterns and an allopatric distribution. Argyrops bleekeri larvae [3.3-7.1 mm body length (BL)] and juveniles (6.7-13.0 mm BL) were found in the bay from January to May; nonetheless, they were not collected from the outer bay or in extremely shallow inshore areas such as tidal flats. The results suggest that Argyrops is the most derived red seabream because of its spiny morphology, and it may be a member of an expanding nearshore group of red seabreams, which originally inhabited offshore waters.

Genetic patterns in peripheral marine populations of the fusilier fish Caesio cuning within the Kuroshio Current.

AIM: Mayr's central-peripheral population model (CCPM) describes the marked differences between central and peripheral populations in genetic diversity, gene flow, and census size. When isolation leads to genetic divergence, these peripheral populations have high evolutionary value and can influence biogeographic patterns. In tropical marine species with pelagic larvae, powerful western-boundary currents have great potential to shape the genetic characteristics of peripheral populations at latitudinal extremes. We tested for the genetic patterns expected by the CCPM in peripheral populations that are located within the Kuroshio Current for the Indo-Pacific reef fish, Caesio cuning. METHODS: We used a panel of 2,677 SNPs generated from restriction site-associated DNA (RAD) sequencing to investigate genetic diversity, relatedness, effective population size, and spatial patterns of population connectivity from central to peripheral populations of C. cuning along the Kuroshio Current. RESULTS: Principal component and cluster analyses indicated a genetically distinct lineage at the periphery of the C. cuning species range and examination of SNPs putatively under divergent selection suggested potential for local adaptation in this region. We found signatures of isolation-by-distance and significant genetic differences between nearly all sites. Sites closest to the periphery exhibited increased within-population relatedness and decreased effective population size. MAIN CONCLUSIONS: Despite the potential for homogenizing gene flow along the Kuroshio Current, peripheral populations in C. cuning conform to the predictions of the CCPM. While oceanography, habitat availability, and dispersal ability are all likely to shape the patterns found in C. cuning across this central-peripheral junction, the impacts of genetic drift and natural selection in increasing smaller peripheral populations appear to be probable influences on the lineage divergence found in the Ryukyu Islands.

Effects of causeway construction on environment and biota of subtropical tidal flats in Okinawa, Japan.

Okinawa, Japan is known for its high marine biodiversity, yet little work has been performed on examining impacts of numerous large-scale coastal development projects on its marine ecosystems. Here, we examine apparent impacts of the construction of the Kaichu-Doro causeway, which was built over 40 years ago. The causeway is a 4.75 km long embankment that divides a large tidal flat and has only two points of water exchange along its entire length. We employed quadrats, transects, sampling, visual surveys, and microbial community analyses combined with environmental, water quality data, and 1m cores, at five stations of two paired sites each (one on each side of Kaichu-Doro) to investigate how the environment and biota have changed since the Kaichu-Doro was built. Results indicate reduction in water flow, and site S1 was particularly heavily impacted by poor water quality, with low diversity and disturbed biotic communities.

A review of the genus Pempheris (Perciformes, Pempheridae) of the Red Sea, with description of a new species.

Four species of the fish genus Pempheris are recognized for the Red Sea: P. adusta Bleeker, 1877; P. mangula Cuvier, 1829; P. nesogallica Cuvier in Cuvier & Valenciennes, 1831; and a new species P. tominagai. All are wide-ranging in the western Indian Ocean, and P. mangula has migrated via the Suez Canal to the eastern Mediterranean Sea. Morphological and genetic analysis of 15 species in this genus show that P. adusta, a widely distributed species, that can't be divided into different species, because of the continuity of morphologies and distribution, and lack of variance in genetics between Indian Ocean, Red Sea, and Pacific Ocean populations. This confirms that the two subspecies described by Randall et al. (2013) are both synonyms of P. adusta. Pempheris adusta is distinguished from other species by a blackish spot on pectoral fin base, pored lateral-line scales 56-64, scale rows above lateral line 4 1/2-6 1/2, distinct blackish band on outer edge of anal fin, and blackish band on posterior edge of caudal fin. Pempheris mangula was named by Cuvier (1829) in a footnote making reference to a drawing and short description in Russell (1803) of a Pempheris from southeast India, giving only the native name ''Mangula-Kutti'', and listing no specimen. The wide distribution of this species, from the Indian Ocean to the Red Sea is also demonstrated by morphological and genetic analysis. Thus, the specimen collected from southern India is herein designated as the neotype. This species is distinguished from other species by its huge eye, deep body, blackish tip of the dorsal fin, pored lateral-line scales 49-60, and scale rows above lateral line 4 1/2-5 1/2. The extant syntype of Kossmann & Räuber's P. rhomboidea is designated as the lectotype of the species; however, P. rhomboidea is a synonym of P. mangula. In addition, Kossmann & Räuber's Pempheris erythraea and P. russellii Day, 1888 are also synonyms of P. mangula. Of two existing syntypes of P. nesogallica from Mauritius, one is designated as the lectotype, the other is re-identified as P. mangula; P. nesogallica is presently known only from the southern Red Sea. This species has a similar morphology to P. mangula, but can be distinguished by a smaller eye than P. mangula, and lack irregular faint longitudinal light stripes on the body side. Pempheris tominagai are distinguished from P. schwenkii Bleeker 1855, formerly misidentified, by the form of posterior nostril, scale counts, color of caudal fin, and by a 2.1% mitochondrial DNA sequence divergence. 

Pempheris ufuagari sp. nov., a new species in the genus Pempheris (Perciformes, Pempheridae) from the oceanic islands of Japan.

Pempheris ufuagari sp. nov. is described based on 10 specimens, 143.9-196.8 mm in standard length, collected from Mi-nami Daito Island and Ogasawara Islands, which are oceanic islands of Japan. Pempheris ufuagari is characterized by a distinct black spot on the pectoral fin base, a bright yellow dorsal and caudal fin, and a blackish band on the outer margin of the anal fin. Pempheris oualensis also has a large body and a distinct black spot on the pectoral fin base, and forms mixed schools with P. ufuagari, but can be distinguished by the different fin coloration (dorsal and caudal fin brown or pale; no blackish band on anal fin margin), and the presence of a villiform tooth band extending outside the lips. Although P. otaitensis, which is found in French Polynesia and Samoa, has similar coloration as P. ufuagari, the latter has lower scale counts than those of the former species: pored lateral-line scales 62-71 (vs. 70-79); scale rows above lateral line 6 1/2-7 1/2 (vs. 8 1/2); predorsal scales 37-43 (vs. 44-48).

Biogeography and evolution of the Carassius auratus-complex in East Asia.

BACKGROUND: Carassius auratus is a primary freshwater fish with bisexual diploid and unisexual gynogenetic triploid lineages. It is distributed widely in Eurasia and is especially common in East Asia. Although several genetic studies have been conducted on C. auratus, they have not provided clear phylogenetic and evolutionary descriptions of this fish, probably due to selection bias in sampling sites and the DNA regions analysed. As the first step in clarifying the evolutionary entity of the world's Carassius fishes, we attempted to clarify the phylogeny of C. auratus populations distributed in East Asia. RESULTS: We conducted a detailed analysis of a large dataset of mitochondrial gene sequences [CR, 323 bp, 672 sequences (528 sequenced + 144 downloaded); CR + ND4 + ND5 + cyt b, 4669 bp in total, 53 sequences] obtained from C. auratus in East Asia. Our phylogeographic analysis revealed two superlineages, one distributed mainly among the Japanese main islands and the other in various regions in and around the Eurasian continent, including the Ryukyus and Taiwan. The two superlineages include seven lineages with high regional specificity that are composed of endemic populations indigenous to each region. The divergence time of the seven lineages was estimated to be 0.2 million years ago (Mya) by a fossil-based method and 1.0-1.9 Mya by the molecular clock method. The antiquity and endemism of these lineages suggest that they are native to their respective regions, although some seem to have been affected by the artificial introduction of C. auratus belonging to other lineages. Triploids of C. auratus did not form a monophyletic lineage but were clustered mostly with sympatric diploids. CONCLUSIONS: The results of the present study revealed the existence of two superlineages of C. auratus in East Asia that include seven lineages endemic to each of the seven regions examined. The lack of substantial genetic separation between triploids and diploids indicates that triploids are not composed of a single independent lineage. The ancient origins and evolutionary uniqueness of the seven lineages warrant their conservation. An overall phylogenetic framework obtained from the present study will be of use for estimating the phylogenetic relationships of Carassius fishes on the Eurasian continent.

Peculiar circular and C-shaped injuries on a body from the sea.

A case where a body with unusual circular injuries was found in the sea is presented. The victim was a 60-year-old woman who had been depressed and had attempted suicide before. She was missing for 6 days before the corpse was found. The body had several almost perfectly circular injuries and C-shaped incision injuries with almost circular flaps of skin. We concluded that the cause of the peculiar circular injuries might be bite marks of Isistius spp. (I. brasiliensis and/or I. plutodus), commonly known as cookie-cutter shark because of its very unusual feeding style.