Yuji Okazaki

Entrainment of coastal water into a frontal eddy of the Kuroshio and its biological significance

The Pacific coastal areas of Japanese Island are major spawning grounds of various fishes. It is considered that large amount of eggs and larvae are dragged into the Kuroshio front so that the survival of fish larvae at the front is important for their recruitment. From this viewpoint, a low-salinity water mass, which was withdrawn from the coastal area to the Kuroshio front, was investigated by drifters, in addition to fine-scale hydrographic observations and water sampling in and around the Kuroshio frontal area off Enshu-nada. The drifters were transported to the east within the low-salinity water along the Kuroshio front in the first stage, and were thereafter entrained into an eddy, which was caused by the frontal meander. They moved closely to each other along the front, but diverged in the eddy. This movement of the drifters coincided with the deformation of low-salinity water mass; the low-salinity water concentrated at the Kuroshio front surrounded by strong salinity gradients at first, while it spread out horizontally and became vague in the shallow surface layer in the frontal eddy. Comparing temperature sections across the front, the strong upwelling was detected in the eddy. Limiting factors for primary production and growth rates were calculated in six sections using the observed temperatures and concentrations of nutrients. In the frontal area of the Kuroshio, low concentration of nutrients limited the primary production shallower than 50 m. Due to the low productivity, concentration of chlorophyll a in the low-salinity water tended to decrease, although the initial concentration was high. Once the coastal water mass was entrained into the frontal eddy, on the contrary, the concentration recovered due to the enhanced primary production in the subsurface layer supported by the upwelling of nutrient-rich water. Fish larvae in the low-salinity water are assumed to use the new production in the eddy; otherwise, they would starve. The entrainment process, which was probably caused by offshoreward movement of the Kuroshio, holds the key to successive survival and recruitment of fish larvae in the Kuroshio system.

Effects of frontal eddies on the distribution and food availability of anchovy larvae in the Kuroshio Extension

The frontal area of the Kuroshio Extension was observed in June 1997 and May 1999. In 1997, anchovy larvae were most abundant in a frontal region of the eddy generated in association with a northward intrusion of warm water from the Kuroshio Extension. High nutrient concentrations apparently overlapped with the larval aggregation, while chlorophyll-a concentration was rather low all over the region. In 1999, observations were made along a two-day trajectory of a drifter released from the eddy centre, which was recognized by a satellite image. Chlorophyll-a concentration was high in the eddy centre but decreased with time. By contrast, abundance of copepod nauplii in the eddy increased with time, and eventually doubled. These results suggest that the frontal eddy contributes to both copepod production and horizontal entrainment or aggregation of anchovy larvae in the frontal region. The frontal eddy possibly benefits the growth and survival of fish larvae in the oligotrophic oceanic water of the Kuroshio Extension region.

Carbon source and trophic position of pelagic fish in coastal waters of south-eastern Izu Peninsula, Japan, identified by stable isotope analysis

It is important to clarify trophic dynamics in marine ecosystems for management of the fishing ground. Organic carbon sources and trophic position of pelagic fishes in the coastal waters of the south-eastern Izu Peninsula, Japan, were examined on the basis of carbon and nitrogen stable isotope distributions. The δ13C of the fishes was mostly distributed from −19 to −16‰ for nektonic fishes (13 species of adults and immatures) and planktonic fishes (10 species of larvae and juveniles), close to the δ13C values of particulate organic matter and planktonic decapods. These δ13C signatures for the inhabitants of the water column were in contrast with the high δ13C values (mainly −16 to −13‰) for demersal fishes of Scorpaeniformes and benthic polychaetes collected in the surf zone. These results indicate that nektonic and planktonic fishes depend on phytoplankton for carbon supply. The δ15N signatures suggest that the trophic position ranged 3.1–4.5 for the nektonic fishes and 2.9–3.7 for the planktonic fishes, premised on trophic level 3 for larval Japanese anchovy Engraulis japonicus. Thus, planktivorous fishes should be mainly assigned to trophic levels 3 and 4 in this area.

Anticipation in Japanese families with schizophrenia

AbstractThe identification of anticipation in schizophrenia is a recent focus in the genetic epidemiology of schizophrenia, although it involves some controversial methodological issues. We explored the evidence of anticipation among 44 Japanese two-generation pairs with schizophrenia found by reviewing nine years of admission records (1986–1994) at the Department of Neuropsychiatry, Nagasaki University Hospital and Michino-o Hospital, Nagasaki. The 44 pairs consisted of 27 two-generation pairs of first-degree relatives group (FDRG) and 17 pairs of second-degree relatives group (SDRG). On pairwise comparison and a life table analysis, the age at onset (AO) was significantly earlier in the lower generation (G2) than in the upper generation (G1) in all of the pairs and in the two subgroups, FDRG and SDRG. Earlier AO was shown in G2 even after minimizing some statistical biases for the study of anticipation in schizophrenia. A significant earlier mean AO was found in G2 even when a cohort effect was controlled for. There was no marked difference in AO between paternal and maternal transmission. These results provide further evidence for epidemiological anticipation, suggesting biological anticipation such as the involvement of trinucleotide repeats expansion in G2. The limitations of the study are also discussed.

Dimensions of schizophrenic positive symptoms: an exploratory factor analysis investigation

Abstract Current psychopathology classifies schizophrenic positive symptoms into four groups: delusions, hallucinations, formal thought disorder, and catatonic symptoms. The present study explores the factor structure of different positive symptoms to refine this classification. The 35 positive symptoms of 429 psychiatric patients, consecutively admitted to any of 95 mental hospitals, with diagnosis of the ICD-10 F20 schizophrenia, were studied. After excluding those items with a base rate of 10% or less, factor analysis yielded six factors. The first factor was loaded by most of Schneider’s first-rank symptoms and two specific auditory hallucinations; the second by all the catatonic symptoms and incoherence; the third by bodily delusions/hallucinations; the fourth by delusions of persecution and reference; the fifth by grandiose and religious delusions; and the sixth by visual and miscellaneous hallucinations. The finding that schizophrenic positive symptoms may have more than four dimensions suggests the need for reclassification of schizophrenic symptoms and for reconsideration of evidence-based diagnostic criteria for the disorder.

Fukushima-derived radionuclides 134Cs and 137Cs in zooplankton and seawater samples collected off the Joban-Sanriku coast, in Sendai Bay, and in the Oyashio region

The Fukushima Dai-ichi nuclear power plant (FNPP) accident that followed the Great East Japan Earthquake in 2011 resulted in the release of enormous quantities of anthropogenic radionuclides, especially radioactive cesium (134Cs and 137Cs) into the ocean off the east coast of Japan. FNPP-derived radioactive Cs may have consequently accumulated within marine food webs via seawater intake and predator–prey interactions. We provide evidence of the temporal variability in 134Cs and 137Cs concentrations in seawater and zooplankton samples collected in coastal waters off Joban-Sanriku, in Sendai Bay, and in the Oyashio region between June 2011 and December 2013. In Sendai Bay, seawater 134Cs and 137Cs concentrations exceeded 1xa0Bq/kg in June 2011 and rapidly decreased during the study period. 134Cs and 137Cs concentrations in zooplankton were also high in June 2011, up to 23xa0Bq/kg-wet and also decreased during the study period, although at a slower rate than seawater 134Cs and 137Cs concentrations. Regarding 137Cs concentrations, the difference in the rate of decrease between seawater and zooplankton resulted in a high apparent concentration ratio (aCR) for zooplankton. The observed relation between 137Cs in seawater and the aCR of zooplankton were good indicators of the progress of 137Cs contamination in zooplankton from the beginning of the FNPP accident to the restoration phase.

Further Evidence of Westernization of Dementia Prevalence in Nagasaki, Japan, and Family Recognition

The present study examined the prevalence of dementia in the Nagasaki Prefecture. The purposes of our investigation were (a) to study the relationship between aging and the prevalence of dementia and the ratio of Alzheimers disease (AD) to vascular dementia (VD), (b) to understand the features of early-onset dementia as seen in patients from 60 to 65 years, and (c) to examine the recognition of dementia by family members. The subjects of the study, a total of 4,368, were all 60 years old and over and were residing in the three areas of Nagasaki Prefecture at the time of the investigation, August 1995. We adopted a two-stage design. The first-stage questionnaire that we developed was delivered to subjects, and we selected for the second stage those subjects who met the criteria outlined in the Methods section. The second-stage investigation was an interview by community nurses and psychiatrists. The prevalence of dementia in subjects 60 years and over was 6.2% (men: 5.9%; women: 6.8%). The prevalence increased with age. The AD/VD ratio was 1.4, and was similar to the recent trend in Japan in that the ratio has reversed to resemble the western pattern. In regard to the family members recognition of illness, the higher the severity of dementia, the higher the recognition ratio of family members became. Only half of these subjects were recognized as having dementia by their family members. In conclusion, the westernization of the AD/VD ratio in Japan was proved. There was little study about family recognition of dementia. In this study, it was remarkable that only half of the subjects were recognized as having dementia by their family members.

Feeding Strategy of Japanese Sand Lance Larvae in Relation to Ciliated Protozoa in the Vicinity of a Thermohaline Front

Larval feeding and survival strategies are described on a Japanese sand lance, Ammodytes personatus Girard, collected in the vicinity of a thermohaline front in the Ise Bay, in comparison with those of other predominant larvae, Hexagrammos spp. and Sebastiscus marmoratus (Cuvier). First-feeding A. personatus larvae (3.1–3.9 mm NL) fed primarily on tintinnid ciliates, subsequently switching to copepod nauplii (4.0–7.9 mm NL larvae) and post-naupliar copepods (8.0–11.3 mm NL larvae). First-feeding Hexagrammos spp. larvae (6.5–6.9 mm NL) fed primarily on post-naupliar copepods, and first-feeding S. marmoratus larvae (<4.0 mm NL), mostly on copepod nauplii. The different food preferences of these species at first-feeding were related to their different mouth widths (0.15–0.19, 0.52–0.56 and 0.32–0.40 mm, respectively) and/or body size (3.1–3.9, 6.5–6.9 and 3.2–3.9 mm NL, respectively). Ciliate-feeding by first-feeding A. personatus larvae was strongly related to the convergence of the larvae and their prey near the thermohaline front, densities of both being greater on the inshore side of the frontal zone. In conclusion, the aggregation of ciliates near the thermohaline front may have improved feeding conditions and survival of first-feeding A. personatus larvae.

MORPHOLOGICAL BRAIN IMAGING STUDIES ON MAJOR PSYCHOSES

The first application of computed tomographic scan to the schizophrenic brain by Johnstone et al. initiated a new neuroscience research era with new perspectives on the neurobiological aspects of major psychoses. The most common paradigm in the flurry of brain imaging studies following the first report was the case—control study comparing controls and patients with major psychoses. However, some application was also made of sophisticated case—control paradigms, such as comparisons between affected and non‐affected identical twins discordant for schizophrenia. Very few prospective cohort studies have been applied in this field. During the past two decades of studies, several brain morphological features have converged. Both schizophrenics and patients with affective disorders showed subtle but significant quantitative differences in brain structures compared with controls. For schizophrenia, the differences were in the lateral and third ventricles, medial temporal lobe, supratemporal gyrus, frontal lobe and such subcortical nuclei as striatum and thalamus. For affective disorders, they were in the cortical sulci, lateral ventricle, striatum, pituitary and adrenal glands. Generally, the differences were greater in schizophrenics, in males and on the left side than in patients with affective disorders, in females and on the right side. Qualitative morphological abnormalities such as T2‐weighted hyperintensity were also demonstrated in elderly patients with affective disorders. For both schizophrenia and affective disorders, abnormal anatomical neurocircuit models of the respective pathophysiologies have been proposed to explain the brain multi‐lesions. Some recommendations for future research in the structural brain imaging of major psychoses have also been proposed.

Distribution and abundance of copepod nauplii in southern part of the East China Sea: implications for prey availability to jack mackerel Trachurus japonicus larvae

In the southern part of the East China Sea (ECS), a large spawning ground of jack mackerel Trachurus japonicus has recently been found: Larval survival during the period of transport from the spawning ground along the shelf break is potentially a critical stage prior to recruitment. As such, the distribution of copepod nauplii in this region was investigated during the main spawning period in 2003–2006. The average naupliar density in 2003 was significantly higher than the other years along the shelf break, which is a major transport pathway for jack mackerel larvae (sea-surface temperature 20–23°C). Estimated egg production rates for Paracalanus spp., one of the most dominant genera of copepods in the southern ECS, based on temperature and chlorophyll-a concentration could not fully explain the spatial and annual variation in naupliar distribution and abundance. Although naupliar densities showed significant positive correlations with chlorophyll-a concentration for all years, an analysis of covariance revealed that naupliar density in 2003 was high even if the effect of chlorophyll-a concentration was excluded. This suggests that apart from copepod production, adult female distribution plays an important role in variability of the naupliar distribution and abundance in the southern ECS.