Larger yellow-phase Japanese eels show short-range homing in a freshwater river.

The homing behavior and site fidelity to habitats in various fishes, including anguillid eels (genus Anguilla), are fascinating. However, little is known about how yellow-phase eels exhibit homing behavior and the sensory mechanisms involved. Using acoustic telemetry, we investigated the homing behavior of 18 Japanese eels, A. japonica, with total lengths ranging from 204 to 570 mm, in a narrow freshwater river in inland central Japan, where salinity gradient, tidal current, and magnetic sense cannot be used for their homing, but where olfaction could play a role. The tagged eels captured upstream and downstream were released downstream and upstream, respectively. The results showed that large eels, over approximately 400 mm in total length, exhibited homing behavior to their original sampling locations (likely to shelters and foraging sites, where they probably spent a longer time than in other locations and grew successfully) from outside their home ranges, predominantly during the dark period. Homing success was not affected by the two capture locations, indicating that eels did not use olfactory cues for short-range homing in freshwater rivers.

Trophic niche partitioning and intraspecific variation in food resource use in the genus Pangasianodon in a reservoir revealed by stable isotope analysis of multiple tissues.

Understanding the mechanism by which non-native fish species integrate into native communities is crucial for evaluating the possibility of their establishment success. The genus Pangasianodon, comprising Pangasianodon gigas and Pangasianodon hypophthalmus, has been introduced into reservoirs, which are non-native habitats, for fishery stock enhancement. P. gigas and P. hypophthalmus often successfully establish and co-occur in several Thai reservoirs, but there is little information on differences in food resource use between the two species. To investigate the trophic niche width of P. gigas and P. hypophthalmus in a Thai reservoir, we conducted stable carbon and nitrogen ratio (δ13C and δ15N) analyses. We examined the degree of individual specialization in both species using the δ13C and δ15N values of muscle and liver tissues, which provides long- and short-term diet information. The isotopic niches did not overlap between P. gigas and P. hypophthalmus. The δ15N value of P. gigas was significantly higher than that of P. hypophthalmus, whereas the δ13C value did not significantly differ between the two species. The isotopic niche sizes were larger in P. hypophthalmus than in P. gigas. Individual specialization was observed in P. hypophthalmus but not in P. gigas, indicating that intraspecific variation in food resource use was larger in P. hypophthalmus compared to P. gigas. These findings suggest that trophic niche partitioning was one of the factors facilitating the establishment success of P. gigas and P. hypophthalmus in a reservoir, but the establishment process may differ between the two species.

Effects of forest cover on richness of threatened fish species in Japan.

Estuaries--one of the most vulnerable ecosystems globally--face anthropogenic threats, including biodiversity loss and the collapse of sustainable fisheries. Determining the factors contributing to the maintenance of estuarine biodiversity, especially that of fish, is vital for promoting estuarine conservation and sustainability. We used environmental DNA metabarcoding analysis to determine fish species composition in 22 estuaries around Japan and measured watershed-scale land-use factors (e.g., population size, urban area percentage, and forest area percentage). We sought to test the hypothesis that the richness of the most vulnerable estuarine fish species (i.e., registered by the Japanese Ministry of the Environment in the national species red-list) is determined by watershed-scale land-use factors. The richness of such species was greater, where forest cover was highest; thus, forest cover contributes to their conservation. The proportion of agriculture cover was associated with low species richness of red-listed fishes (redundancy analysis, adjusted R2 = 43.9% of total variance, df = 5, F = 5.3843, p = 0.0001). The number of red-listed species increased from 3 to 11 along a watershed land-use gradient ranging from a high proportion of agriculture cover to a large proportion of forest cover. Furthermore, the results showed that throughout Japan all the examined watersheds that were covered by >74.8% forest had more than the average (6.7 species per site) richness of red-listed fish species. This result can be attributed to the already high average forest cover in Japan of 67.2%. Our results demonstrate how the land use of watersheds can affect the coastal sea environment and its biodiversity and suggest that proper forest management in conjunction with land-use management may be of prime importance for threatened fish species and coastal ecosystems in general.

Efectos de la Cobertura Forestal sobre la Riqueza de Especies Amenazadas de Peces en Japón Resumen Los estuarios-uno de los ecosistemas más vulnerables a nivel mundial-enfrentan amenazas causadas por el hombre, incluyendo la pérdida de biodiversidad y el colapso de las pesquerías sustentables. La determinación de los factores que contribuyen al mantenimiento de la biodiversidad estuarina, especialmente la de los peces, es vital para fomentar la conservación y sustentabilidad estuarinas. Usamos un análisis de metasecuenciación de ADN ambiental para determinar la composición de especies de peces en 22 estuarios de Japón y medimos los factores del uso de suelo a nivel de cuenca (p. ej.: tamaño poblacional, porcentaje de área urbana y porcentaje de área forestal). Buscamos probar la hipótesis de que la riqueza de las especies de peces más vulnerables (es decir, aquellas registradas por el Ministerio Japonés del Ambiente en la lista roja de especies a nivel nacional) está determinada por los factores de uso de suelo a nivel de cuenca. La riqueza de dichas especies fue mayor en donde la cobertura forestal era la más alta; por lo tanto, la cobertura forestal contribuye a la conservación de estas especies. La proporción de la cobertura agrícola estuvo asociada con una baja riqueza de especies de peces en la lista roja (análisis de redundancia, R2 ajustada = 43.9% de la varianza total, gl = 5, F = 5.3843, p = 0.0001). El número de especies en la lista roja incrementó de 3 a 11 a lo largo del gradiente de uso de suelo de la cuenca, yendo desde una proporción alta de cobertura agrícola a una proporción alta de cobertura forestal. Además, los resultados mostraron que, en Japón, todas las cuencas analizadas que contaban con una cobertura forestal >74.8% tenían mayor riqueza de especies de peces en la lista roja que el promedio (6.7 especies por sitio). Este resultado puede atribuirse a la ya de por sí elevada cobertura forestal de Japón (67.2%). Nuestros resultados demuestran cómo el uso de las cuencas puede afectar al ambiente costero marino y a su biodiversidad y sugiere que la gestión adecuada de los bosques en conjunto con el manejo del uso de suelo puede ser de suma importancia para las especies amenazadas de peces y los ecosistemas costeros en general.

Patterns of genomic divergence and introgression between Japanese stickleback species with overlapping breeding habitats.

With only a few absolute geographic barriers in marine environments, the factors maintaining reproductive isolation among marine organisms remain elusive. However, spatial structuring in breeding habitat can contribute to reproductive isolation. This is particularly important for marine organisms that migrate to use fresh- or brackish water environments to breed. The Japanese Gasterosteus stickleback species, the Pacific Ocean three-spined stickleback (G. aculeatus) and the Japan Sea stickleback (G. nipponicus) overwinter in the sea, but migrate to rivers for spawning. Although they co-occur at several locations across the Japanese islands, they are reproductively isolated. Our previous studies in Bekanbeushi River showed that the Japan Sea stickleback spawns in the estuary, while the Pacific Ocean stickleback mainly spawns further upstream in freshwater. Overall genomic divergence was very high with many interspersed regions of introgression. Here, we investigated genomic divergence and introgression between the sympatric species in the much shorter Tokotan River, where they share spawning sites. The levels of genome-wide divergence were reduced and introgression was increased, suggesting that habitat isolation substantially contributes to a reduction in gene flow. We also found that genomic regions of introgression were largely shared between the two systems. Furthermore, some regions of introgression were located near loci with a heterozygote advantage for juvenile survival. Taken together, introgression may be partially driven by adaptation in this system. Although, the two species remain clearly genetically differentiated. Regions with low recombination rates showed especially low introgression. Speciation reversal is therefore likely prevented by barriers other than habitat isolation.

Migration, residency and habitat utilisation by wild and cultured Japanese eels (Anguilla japonica) in a shallow brackish lagoon and inflowing rivers using acoustic telemetry.

This study monitored post-release movements of 20 wild Japanese eels (Anguilla japonica) [mean ± S.D. 520.8 ± 92.3 mm total length (TL), 217.9 ± 146.3 g body mass (BM)] in a brackish water lagoon in northeastern Japan using acoustic telemetry to elucidate how wild Japanese eels use different river, estuary and marine environments. In addition, 12 cultured Japanese eels (TL = 578.9 ± 18.0 mm, BM = 344.9 ± 25.5 g) were released to understand the comparative behaviours of wild and cultured eels. Both types of eels were simultaneously released in the southern inner part of the lagoon in September 2016 where there are freshwater influences from a river. Following release, eight of the wild eels (40%) were largely sedentary near the released point (river mouth) and stayed at the site for overwinter. Nonetheless, several individuals showed behavioural plasticity of habitat use: three wild eels moved towards the northern part of the lagoon with stronger influence from the sea during May-July 2017. Two wild eels showed clear repeated movements from the lagoon to a river at night and returned to the lagoon by dawn for more than a week every day, and one wild eel migrated upstream for overwintering. Signals from 55% of the wild eels could be detected for more than 6 months, whereas those from all of the cultured eels were lost by December 2016, indicating a short resident time of large cultured eels (BM > 200 g) released in a brackish water area. One wild silver eel migrated to the outer sea during the ebb tide at night in November 2016, probably triggered by the decrease in water temperature (from c. 20°C to c. 13°C), and seven cultured eels similarly moved to the outer sea during October-November 2016. The results revealed the similarities (e.g., nocturnal movements) and differences (e.g., stay period and seasonal movements) in the behavioural characteristics of wild and cultured eels and indicated that habitat connectivity among river, estuary and coastal waters is crucial for enabling eels to efficiently utilise these productive habitats through their behavioural plasticity.

Multiple waves of freshwater colonization of the three-spined stickleback in the Japanese Archipelago.

BACKGROUND: The three-spined stickleback (Gasterosteus aculeatus) is a remarkable system to study the genetic mechanisms underlying parallel evolution during the transition from marine to freshwater habitats. Although the majority of previous studies on the parallel evolution of sticklebacks have mainly focused on postglacial freshwater populations in the Pacific Northwest of North America and northern Europe, we recently use Japanese stickleback populations for investigating shared and unique features of adaptation and speciation between geographically distant populations. However, we currently lack a comprehensive phylogeny of the Japanese three-spined sticklebacks, despite the fact that a good phylogeny is essential for any evolutionary and ecological studies. Here, we conducted a phylogenomic analysis of the three-spined stickleback in the Japanese Archipelago. RESULTS: We found that freshwater colonization occurred in multiple waves, each of which may reflect different interglacial isolations. Some of the oldest freshwater populations from the central regions of the mainland of Japan (hariyo populations) were estimated to colonize freshwater approximately 170,000 years ago. The next wave of colonization likely occurred approximately 100,000 years ago. The inferred origins of several human-introduced populations showed that introduction occurred mainly from nearby habitats. We also found a new habitat of the three-spined stickleback sympatric with the Japan Sea stickleback (Gasterosteus nipponicus). CONCLUSIONS: These Japanese stickleback systems differ from those in the Pacific Northwest of North America and northern Europe in terms of divergence time and history. Stickleback populations in the Japanese Archipelago offer valuable opportunities to study diverse evolutionary processes in historical and contemporary timescales.

Gut Morphometry Represents Diet Preference to Indigestible Materials in the Largest Freshwater Fish, Mekong Giant Catfish (Pangasianodon gigas).

The Mekong giant catfish Pangasianodon gigas is one of the largest freshwater fish, measuring up to 3 m in total length. This study was designed to determine the feeding habits of P. gigas to better understand how the fish achieve their large body size. We compared the relationship between gut length (GL) and total length (TL) among related species in superfamily Bagroidea, order Siluriformes (Pangasianodon hypophthalmus and Hemibagrus nemurus) in the Kaeng Krachan reservoir, Thailand. The mean relative gut length (RGL = GL / TL) of P. gigas was 3.50, showing that they have relatively long guts, with values more similar to those of omnivorous P. hypophthalmus (RGL = 3.70) than to those of carnivorous H. nemurus (RGL = 0.92). In the allometric relationship (i.e., log10 GL = log10 a + b log10 TL), the slope close to 1 for P. gigas (b = 1.07) has been widely observed in carnivores, while P. gigas has a greater intercept of the linear equation than P. hypophthalmus and H. nemurus, resulting in a similar GL of P. gigas to omnivorous P. hypophthalmus at approximately 35 cm in TL. Moreover, GL of P. gigas at 150 to 250 cm in TL showed great variations (RGL = 1.35-6.32). The variation in RGL for P. gigas seemed to result from a poor nutritional state. In conclusion, P. gigas is suggested to feed on indigestible materials such as plants, algae, and sediments, and potentially experience fasting in a reservoir.

Phase II study of palonosetron, aprepitant and dexamethasone to prevent nausea and vomiting induced by multiple-day emetogenic chemotherapy.

PURPOSE: This study aimed to determine the antiemetic efficacy and safety of palonosetron, aprepitant and dexamethasone in patients with testicular germ cell tumours (TGCTs) receiving 5-day cisplatin-based combination chemotherapy. METHODS: In this open-label, single-arm, single-centre study, the antiemetic therapy consisted of palonosetron 0.75 mg on day 1, aprepitant 125 mg on day 1 and 80 mg on days 2-7 and dexamethasone 6.6 mg on days 1-7. The primary endpoint was complete response (CR; no vomiting/retching or rescue medication) in the overall period (0-240 h), and secondary endpoints included complete protection (CP; defined as CR and no more than mild nausea) and total control (TC; defined as CR and no nausea). The incidence and severity of nausea were assessed on the basis of the Common Terminology Criteria for Adverse Events v4.0 and a subjective rating scale completed by patients. RESULTS: Twenty-five patients were enrolled and evaluated for safety, and 24 patients were evaluated for efficacy. CR was achieved in 62.5% of patients (95% confidence interval [CI] = 40.6-81.2, p = 0.043) in the overall period. CP and TC were achieved in 62.5% (95% CI = 40.6-81.2) and 25.0% of patients (95% CI = 9.8-46.7), respectively, in the overall period. The primary adverse drug reaction was hiccups (48.0%). The events were expected, and none was grade 3 or 4. CONCLUSIONS: The examined combination antiemetic therapy was effective and well-tolerated in patients with TGCTs receiving 5-day cisplatin-based combination chemotherapy.

Effects of Ascorbyl-2-phosphate Magnesium on Human Keratinocyte Toxicity and Pathological Changes by Sorafenib.

Hand-foot skin reaction is recognized as one of the most common adverse events related to multiple tyrosine kinase inhibitors, but an effective prevention method has not been identified. The chief aim of this study was to find a mechanism-based preventive method for the skin toxicity induced by sorafenib using vitamin C derivatives. The effects of ascorbyl-2-phosphate magnesium (P-VC-Mg) on the molecular and pathological changes induced by sorafenib were investigated in human keratinocyte HaCaT cells. The cell growth inhibition and apoptotic effects of sorafenib were attenuated by P-VC-Mg. Moreover, P-VC-Mg inhibited the decrease of signal transducer and activator of transcription 3 (STAT3) phosphorylation and the expression of apoptosis suppressors treated by sorafenib. HaCaT cells transfected with the STAT3 dominant-negative form (STAT3DN) and STAT3 small interfering RNA (siRNA) combined with P-VC-Mg did not exhibit the attenuation of cell growth inhibition. Interestingly, after exposure to sorafenib in a three dimensional (3D) skin model assay, the basal layer was significantly thickened and the granular and spinous layers became thinner. In contrast, after exposure to sorafenib with P-VC-Mg, the thickness of the basal, granular, and spinous layers was similar to that of the control image. These findings suggest that P-VC-Mg attenuates sorafenib-induced apoptosis and pathological changes in human keratinocyte cells and in the 3D skin model mediated by the maintenance of STAT3 activity.

Sex chromosome turnover contributes to genomic divergence between incipient stickleback species.

Sex chromosomes turn over rapidly in some taxonomic groups, where closely related species have different sex chromosomes. Although there are many examples of sex chromosome turnover, we know little about the functional roles of sex chromosome turnover in phenotypic diversification and genomic evolution. The sympatric pair of Japanese threespine stickleback (Gasterosteus aculeatus) provides an excellent system to address these questions: the Japan Sea species has a neo-sex chromosome system resulting from a fusion between an ancestral Y chromosome and an autosome, while the sympatric Pacific Ocean species has a simple XY sex chromosome system. Furthermore, previous quantitative trait locus (QTL) mapping demonstrated that the Japan Sea neo-X chromosome contributes to phenotypic divergence and reproductive isolation between these sympatric species. To investigate the genomic basis for the accumulation of genes important for speciation on the neo-X chromosome, we conducted whole genome sequencing of males and females of both the Japan Sea and the Pacific Ocean species. No substantial degeneration has yet occurred on the neo-Y chromosome, but the nucleotide sequence of the neo-X and the neo-Y has started to diverge, particularly at regions near the fusion. The neo-sex chromosomes also harbor an excess of genes with sex-biased expression. Furthermore, genes on the neo-X chromosome showed higher non-synonymous substitution rates than autosomal genes in the Japan Sea lineage. Genomic regions of higher sequence divergence between species, genes with divergent expression between species, and QTL for inter-species phenotypic differences were found not only at the regions near the fusion site, but also at other regions along the neo-X chromosome. Neo-sex chromosomes can therefore accumulate substitutions causing species differences even in the absence of substantial neo-Y degeneration.

A role for a neo-sex chromosome in stickleback speciation.

Sexual antagonism, or conflict between the sexes, has been proposed as a driving force in both sex-chromosome turnover and speciation. Although closely related species often have different sex-chromosome systems, it is unknown whether sex-chromosome turnover contributes to the evolution of reproductive isolation between species. Here we show that a newly evolved sex chromosome contains genes that contribute to speciation in threespine stickleback fish (Gasterosteus aculeatus). We first identified a neo-sex chromosome system found only in one member of a sympatric species pair in Japan. We then performed genetic linkage mapping of male-specific traits important for reproductive isolation between the Japanese species pair. The neo-X chromosome contains loci for male courtship display traits that contribute to behavioural isolation, whereas the ancestral X chromosome contains loci for both behavioural isolation and hybrid male sterility. Our work not only provides strong evidence for a large X-effect on reproductive isolation in a vertebrate system, but also provides direct evidence that a young neo-X chromosome contributes to reproductive isolation between closely related species. Our data indicate that sex-chromosome turnover might have a greater role in speciation than was previously appreciated.

Apoptotic Effects of the Extracts of Cordyceps militaris via Erk Phosphorylation in a Renal Cell Carcinoma Cell Line.

Cordyceps militaris (CM) is gaining attention as a traditional medicinal food, but its molecular biological mechanisms for anti-cancer activity are not identified or clarified. We aimed to elucidate the synthesizing apoptotic effects of CM extracts and to determine the biological effects of CM extract against cordycepin alone in a renal cell carcinoma (RCC) cell line. CM extract showed higher effects of growth inhibition, apoptotic effect, and cell cycle arrest than cordycepin alone. Moreover, CM extract activated extracellular signal-regulated kinase (Erk) highly more than cordycepin alone. We suggest that cordycepin and CM extract induced apoptosis via the activation of Erk dominantly and AMP-activated protein kinase slightly; CM extract has more potent effects on apoptotic effects associated with Erk activation than cordycepin alone.

Striped catfish (Pangasianodon hypophthalmus) exploit food sources across anaerobic decomposition- and primary photosynthetic production-based food chains.

Dietary information from aquatic organisms is instrumental in predicting biological interactions and understanding ecosystem functionality. In freshwater habitats, generalist fish species can access a diverse array of food sources from multiple food chains. These may include primary photosynthetic production and detritus derived from both oxic and anoxic decomposition. However, the exploitation of anoxic decomposition products by fish remains insufficiently explored. This study examines feeding habits of striped catfish (Pangasianodon hypophthalmus) at both adult and juvenile stages within a tropical reservoir, using stable carbon, nitrogen, and sulfur isotope ratios (δ13C, δ15N, and δ34S, respectively) and fatty acid (FA) analyses. The adult catfish exhibited higher δ15N values compared to primary consumers that feed on primary photosynthetic producers, which suggests ingestion of food sources originating from primary photosynthetic production-based food chains. On the other hand, juvenile catfish demonstrated lower δ15N values than primary consumers, correlating with low δ34S value and large proportions of bacterial FA but contained small proportions of polyunsaturated FA. This implies that juveniles utilize food sources from both anoxic decomposition and primary photosynthetic production-based food chains. Our results indicate that food chains based on anoxic decomposition can indeed contribute to the dietary sources of tropical fish species.

[Effects of aprepitant in daily administrations of low-dose cisplatin].

OBJECTIVE: While aprepitant is actually recommended for the prevention of nausea and vomiting induced by a single cisplatin administration, it is still unclear whether it has a clinical benefit when administered along with daily administrations of low- dose cisplatin(20mg/m2 days 1-5). This study was conducted to evaluate the efficacy of aprepitant in patients receiving daily administration of low-dose cisplatin. METHODS: Our study focused on 25 patients who received cancer therapy including cisplatin, with or without aprepitant (days 1-5). We performed a retrospective study to identify any significant positive effect of aprepitant in the prevention of nausea and vomiting for 10 days(days 1-10). Because cisplatin has a long half-life, we assessed the delayed phase nausea and vomiting(days 6-10). RESULTS AND CONCLUSION: Multiple-day dosing of aprepitant was effective for prevention of nausea(Odds ratio: 0. 30, p= 0. 0012)and vomiting(Odds ratio: 0. 04, p=0. 0001)throughout the observation. Furthermore, we observed a significant positive effect of aprepitant in the prevention of delayed nausea(Odds ratio: 0. 19, p=0. 0083)and vomiting(Odds ratio: 0. 07, p=0. 0040). These findings suggest that multiple-day dosing of aprepitant is useful for the inhibition of acute delayed nausea and vomiting caused by chemotherapy including daily administration of low-dose cisplatin.

Water temperature and precipitation stimulate small-sized Japanese eels to climb a low-height vertical weir.

Although river-crossing structures can have a detrimental effect on the movement and distribution of anguillid eels (genus Anguilla), they have inhabited locations upstream of river-crossing structures in many rivers. However, the growth stage in which the eels start to climb river-crossing structures remains unclear. In this study, we directly observed, using infrared video camera systems, that the Japanese eel (Anguilla japonica) climbs a low-height vertical weir as a migratory barrier, confirming the ability of eels to climb over a low-height weir within a river. All eels climbed the weir at night, between sunset and sunrise. We observed that the total length of Japanese eels that climbed the weir ranged from 60 to 140 mm, suggesting that eels inhabiting the upstream area of a weir climbed it when they were small and then lived and grew upstream. Moreover, the general additive model showed considerable effects of water temperature and precipitation on eel climbing, suggesting that water temperature and precipitation are important for its activation. The results of this study also show the effectiveness of infrared video cameras in monitoring eel climbing, which could be applied to monitor fish migratory behavior through fish passages. The findings of this study are useful for the comprehensive management and conservation of wild eel stocks.

Morphological and Molecular Gonadal Sex Differentiation in the Wild Japanese eel Anguilla japonica.

Most cultured Japanese eels (Anguilla japonica) show male sex differentiation; however, natural gonadal sex differentiation has not been evaluated. In this study, this process was characterized in wild eels. Differentiated ovaries and testes were observed after the eels grew to 320 and 300 mm in total length, respectively. The youngest ovary and testis appeared at 3 and 4 years old, respectively; however, undifferentiated gonads were found up to 7 years, suggesting that sex differentiation was triggered by growth rather than aging. gsdf, amh, foxl2b and foxl3b were highly expressed in the testes, whereas figla, sox3, foxn5, zar1, and zp3 were highly expressed in the ovaries. The expression of cyp19a1a and foxl2a did not differ significantly between the testis and ovary. In the ovaries, the cyp19a1a and foxl2a levels were highest in the early stages, suggesting that their function is limited to early ovarian differentiation. The foxn5, zar1 and zp3 levels tended to increase in the later stages, suggesting that they function after the initiation of ovarian differentiation. In undifferentiated gonads, dimorphic gene expression was not observed, suggesting that the molecular sex differentiation phase is short and difficult to detect. These findings provide the first demonstration of the whole course of natural gonadal sex differentiation in eels at molecular and morphological levels.

Seasonal feeding rhythm associated with fasting period of Pangasianodon gigas: long-term monitoring in an aquarium.

The Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River basin, and is recognized as endangered species, largely due to overfishing and development of the river basin. We monitored food intake of P. gigas in a stable environment in an aquarium over a 6-year period and analyzed their feeding rhythm and fasting periods. The daily food intake for each fish was recorded from 18 June 2004 to 17 June 2010. The feeding rhythm or pattern was determined by the fast Fourier transform (FFT) analysis. The FFT analysis revealed that different cycles of feeding rhythm (168.8, 313.1, and 365.3 days) in three catfishes and no observable cycles in two catfishes. However, three catfishes showed subordinate peaks with approximately 365 days (365.3 days for all). These suggest that, at least, four of five catfish had have approximately 365-days feeding cycle. We also showed that all catfish undergo long-term fasting periods (> 20 days). Of note, the feeding/fasting pattern coincides with the wet/dry seasons in Thailand, which also corresponds to the abundance of the catfish food resource (Cladophora spp.). We found that P. gigas exhibit a seasonal feeding rhythm that is synchronized by food availability. Furthermore, we found that the seasonal feeding rhythm was gradually dampened over time, suggesting that the observed seasonal feeding rhythm with long-term fasting of the catfish is likely controlled by an endogenous clock system. To our knowledge, this is the first case of quantification of the seasonal feeding rhythm with fasting periods in teleost fish.

Evaluation of fish biodiversity in estuaries using environmental DNA metabarcoding.

Biodiversity is an important parameter for the evaluation of the extant environmental conditions. Here, we used environmental DNA (eDNA) metabarcoding to investigate fish biodiversity in five different estuaries in Japan. Water samples for eDNA were collected from river mouths and adjacent coastal areas of two estuaries with high degrees of development (the Tama and Miya Rivers) and three estuaries with relatively low degrees of development (the Aka, Takatsu, and Sendai Rivers). A total of 182 fish species across 67 families were detected. Among them, 11 species occurred in all the rivers studied. Rare fishes including endangered species were successfully detected in rich natural rivers. Biodiversity was the highest in the Sendai River and lowest in the Tama River, reflecting the degree of human development along each river. Even though nutrient concentration was low in both the Aka and Sendai Rivers, the latter exhibited greater diversity, including many tropical or subtropical species, owing to its more southern location. Species composition detected by eDNA varied among rivers, reflecting the distribution and migration of fishes. Our results are in accordance with the ecology of each fish species and environmental conditions of each river.

A key metabolic gene for recurrent freshwater colonization and radiation in fishes.

Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene Fads2 in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of Fads2 in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in Fads2 copies, indicating its key role in freshwater colonization.

Impact of the huge 2011 Tohoku-oki tsunami on the phenotypes and genotypes of Japanese coastal threespine stickleback populations.

On March 11, 2011, a large earthquake occurred, causing a tsunami which struck the Pacific coast of northeast Japan. We investigated the ecological and genetic effects of the large tsunami on the threespine stickleback (genus Gasterosteus) populations in Otsuchi Town, which was one of the most severely damaged areas after the tsunami. Our environmental surveys showed that spring water may have contributed to the habitat recovery. Morphological analysis of the stickleback before and after the tsunami showed morphological shifts in the gill raker number, which is a foraging trait. Genetic analyses revealed that the allelic richness of one population was maintained after the tsunami, whereas that of another decreased in 2012 and then started to recover in 2013. Additionally, we found that the large tsunami and ground subsidence created new spring water-fed pools with sticklebacks, suggesting that the tsunami brought sticklebacks into these pools. Genetic analysis of this population showed that this population might be derived from hybridization between freshwater Gasterosteus aculeatus and anadromous G. nipponicus. Overall, our data indicate that tsunamis can influence morphologies and genetic structures of freshwater fishes. Furthermore, spring water may play important roles in the maintenance and creation of fish habitats, faced with environmental disturbance.