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Seasonal changes in habitat use in terms of depth and temperature were estimated for Japanese flounder Paralichthys olivaceus from the Pacific coast of northeastern Japan from 2006 to 2008, using data from trawl and gillnet fisheries logbooks, to which we assigned monthly estimates of bottom temperature. Estimated distributions of flounder for depth and temperature were validated by actual depth and temperature readings from data storage tags (DSTs) attached to flounder, and from collection records by trawl survey. Year-round, flounder > 300 mm in total length were present mainly in areas

To test whether stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) can be used to understand the ecological connectivity of Japanese flounder Paralichthys olivaceus, we evaluated the isotopic signatures of juvenile P. olivaceus from the Pacific coast of northern Japan (i.e., from Aomori to Ibaraki Prefectures). We measured δ13C and δ15N in muscle and collagen extracted from vertebrae and found that isotope ratios were strongly correlated in both. The discrimination models we developed for muscle and collagen proved useful in distinguishing among juvenile P. olivaceus collected from the five prefectures (Aomori, Iwate, Miyagi, Fukushima, and Ibaraki). Juveniles collected in Aomori in particular showed significantly lower values of δ13C and δ15N than those from the other prefectures, which likely reflects the greater influence of the Tsugaru Warm Current in that region. Because collagen in the vertebral centrum can be used to reconstruct annual isotopic records, our results may also assist in developing migration tracking procedures for adult P. olivaceus along the Pacific coast of northern Japan.

Here we challenge traditional views on the direction of change in teleost body condition and reproductive traits in response to abiotic and biotic factors by studying the data-rich, planktivorous Norwegian spring-spawning herring (NSSH), a member of the abundant Atlantic herring (Clupea harengus) stock complex. To test potential influential factors, we focused on the last twenty years, i.e. a period with ocean warming, a transient but significant drop in zooplankton biomass, and accelerating interspecific competition resulting from primarily Atlantic mackerel (Scomber scombrus) entering these high-latitude waters in large quantities, “the new mackerel era” in the Nordic Seas. Adult NSSH concurrently allocated relatively less to growth in length than weight resulting in higher body condition. Growth likely decreased in warmer waters under stiff prey competition to support reproductive costs. Condition and reproductive responses were not only immediate but were also lagged by three seasons, corresponding to the period when new oocytes are produced. Furthermore, fecundity increased in warmer waters while egg size dropped. Hence, fine-tuned trade-off mechanisms were apparent and varied. We demonstrate that evaluations of reproductive trade-offs based on pooled data are misleading; poor- and good-condition NSSH followed different reproductive trajectories. These findings emphasize difficult-to-predict trends in life-history traits should be tracked longitudinally by the individuals and their aggregate cohort, as they are linked to complex overarching environmental phenomena, like ecosystem carrying capacity and climate fluctuations. publishedVersion

The temperate seabass Lateolabrax japonicus is a coastal and partial amphidromous fish that is commercially valuable in Japan. Fish age is an important and sensitive variable for stock structure assessment, and inaccurate aging can result in inappropriate management practices. However, there have been few studies on age determination in this species. By examining monthly changes in marginal increment growth, we validated that otolith increments are formed annually. This information was used to develop an age-determination method using otolith sections. Von Bertalanffy growth models were generated based on standard length and weight data for both sexes in Sendai Bay and Tango Bay, Japan. Differences in standard length- and weight-at-age and growth parameters were observed in both sexes and locations. Females exhibited larger standard lengths and weights at older ages than did males, in both locations. Individuals from Sendai Bay exhibited longer average asymptotic lengths, higher asymptotic weight, higher standard length-at-age and higher weight-at-age compared to their counterparts from Tango Bay. Decreases in growth rates in both Sendai Bay and Tango Bay occurred around the age at maturity, indicating that more energy was allocated to reproduction than growth after reaching maturation. Differences between Sendai Bay and Tango Bay in the age at which the maximum instantaneous growth rate and the asymptotic length are reached were thought to arise from differences in water temperature and biological productivity between the two bays.

This paper aims to assess the diel feeding pattern and seasonal variation in the daily ration of immature and mature marbled flounder (Pseudopleuronectes yokohamae ). A day‐night collection by bottom trawls was conducted in Sendai Bay in July 2014. Marbled flounder (131–493 mm total length; Number of collected individuals = 1830, Number of analyzed individuals = 497) fed mainly on polychaetes during the day. At night, stomach content weight decreased with time, but the weight and proportion of bivalve siphons were consistently higher at night than during the day, suggesting nocturnal feeding by the flounder on bivalve siphons. Daily ration was greater in females (, This work was partly supported by the Stock Assessment Program of Fisheries Agency and Fisheries Research and Education Agency of Japan and the program “Project on Clarifying the Impact of Nuclear Substances” of the Fisheries Agency of Japan.

Ontogenetic habitat shift and feeding habits in the shallow (

Following general life history theory, immediate reproductive investment (egg mass × fecundity/body mass) in oviparous teleosts is a consequence of both present and past environmental influences. This clarification questions the frequent use of season-independent (general) fecundity formulas in marine fish recruitment studies based on body metrics only. Here we test the underlying assumption of no lag effect on gametogenesis in the planktivorous, determinate-fecundity Atlantic herring (Clupea harengus) displaying large plasticity in egg mass and fecundity, examining Norwegian summer–autumn spawning herring (NASH), North Sea autumn-spawning herring (NSAH), and Norwegian spring-spawning herring (NSSH). No prior reproductive information existed for NASH. Compared with the 1960s, recent reproductive investment had dropped markedly, especially for NSAH, likely reflecting long-term changes in zooplankton biography and productivity. As egg mass was characteristically small for autumn spawners, although large for spring spawners (cf. different larval feeding conditions), fecundity was the most dynamic factor within reproductive investment. For the data-rich NSSH, we showed evidence that transient, major declines in zooplankton abundance resulted in low fecundity over several subsequent seasons, even if Fulton’s condition factor (K) turned high. Temporal trends in Kslope (K on total length) were, however, informative. These results clarify that fecundity is defined by (i) dynamics of primary (standing stock) oocytes and (ii) down-regulation of secondary oocytes, both processes intimately linked to environmental conditions but operating at different timescales. Thus, general fecundity formulas typically understate interannual variability in actual fecundity. We therefore argue for the use of segmented fecundity formulas linked to dedicated monitoring programs.

The determination of the optimum stocking density of hatchery-reared juveniles in relation to the carrying capacity of the nursery ground is important to the success of any stock enhancement programs. In order to estimate the surplus productivity of nursery grounds available to support hatchery-reared fish, a population growth model for juvenile Japanese flounder Paralichthys olivaceus was developed by extending an ecophysiology-based model on growth of juvenile fishes. Parameters of the model were adjusted using field-collected data from Ohno Bay in northeastern Japan. This model predicted the optimum stocking density, namely the maximum number of hatchery-reared juvenile Japanese flounder released into the bay without decreasing the growth of conspecific wild juveniles owing to food limitation. The optimum stocking density for juveniles of 89 mm total length was estimated to be 2000 individuals per 250,000 m2 in Ohno Bay in 1989. Under the model, the most important factors affecting the optimum stocking density of Japanese flounder were the abundance of mysids and wild juveniles at the time of release. The effect of abundance of a competing flatfish species on growth of wild Japanese flounder was less important.

Stocking hatchery fish into the wild should only be implemented at a level that can be sustained within the available food-based carrying capacity to avoid food resource competition with wild conspecifics. We constructed a simulation model to assess the growth of wild conspecifics under different magnitudes of hatchery fish releases, including no releases and actual release levels, and under different wild fish abundancies. Stocking of juvenile Japanese flounder Paralichthys olivaceus (approximately 70–110 mm TL) in Fukushima from 2003 to 2005 was analyzed. We monitored post-release changes in abundance of both cultured and wild juveniles and their prey (mysids). Our survey and modelled simulations revealed that the surplus prey production was sufficient to support the consumption of stocked and wild Japanese flounder (up to 150,000 individuals per site in 2003 and 2004), during which wild juveniles achieved nearly maximum growth rates. However, in 2005, during which a dominant year class of wild Japanese flounder occurred, the body size of wild juveniles was 49% smaller than the predicted size based on the maximum growth rates. This suggests that the food-based carrying capacity was reached in that year. Thus, it is important to evaluate the existing prey and wild juveniles levels and adjust the release accordingly every year.

The impact of the great tsunami, which was generated by the Great East Japan Earthquake on 11 March 2011, on the quality of a nursery ground for juvenile Japanese flounder Paralichthys olivaceus with a sandy bottom of

Food web structures are well-studied, central theme of fisheries science that depicts the pathways of energy flow. Researchers have long been studied on the importance of quantitative estimation of the relative contribution of prey animals in fish by stomach contents analysis. However, this analysis requires experienced technique, and it only reflects recent diets. On the other hand, carbon and nitrogen stable isotope ratios representing average feeding habits and trophic position have become a powerful tool in food web analyses. In this study, to clarify the main resources (feeding habits) and contribution rate of prey animals using these two analyses in Sendai Bay. As a result, the feeding habits by stomach content analysis of dominant ten fish species were classified into four groups; fish feeders, crustacean feeders, benthic feeders and plankton feeders. A dual isotope plot of δ13C and δ15N values supported the classification by stomach content analysis. Most of fish feeders depended on bait fishes (mainly feeding on plankton feeders), and crustacean and benthic feeders depended on crustacean and/or benthos. The contribution rate of prey animals by mixing models for δ13C and δ15N within Bayesian framework, Paralichthys olivaceus in June 2012 was 67% Engraulis japonicus, and 32% Ammodytes personatus. The results of stable isotope analysis were well consistent with the stomach contents analysis.

To identify the origin of various fishes and reconstruct their migration history at the individual level, isotope analysis is a powerful alternative to artificial tagging. We used a novel individual-based methodology to reconstruct individual migratory and/or trophic shifts associated with growth based on isotopic data in the vertebral centrum of adult Japanese flounder Paralichthys olivaceus in Sendai Bay. We measured carbon and nitrogen isotope ratios (δ^13C and δ^15N) in muscle tissues, and conducted a segmental isotope analysis of bulk δ^13C (δ^13Cbulk), bulk δ^15N (δ^15Nbulk), and δ^15N of glutamic acid (δ^15NGlu) and phenylalanine (δ^15NPhe) in vertebral collagen. The δ^15NGlu and δ^15NPhe values for bone collagen revealed an increase in trophic position and a shift to lower trophic baselines (δ^15NBase: indicative of δ^15N values of primary trophic sources) for most individuals. For both δ^13Cbulk and δ^15Nbulk, we detected significant positive correlations between values for muscle and the outermost section of vertebral collagen. A nonlinear time-series analysis of δ^13Cbulk and δ^15Nbulk suggested that a combination of intrinsic (the timing of migration from the nursery to deep offshore areas in juveniles) and extrinsic (habitat and/or food qualities) factors influence the isotopic chronology. A segmental isotope analysis revealed the segregation of individuals among sampling sites at all life stages and changes in trophic positions and δ^15NBase values during growth. Our results suggest that the P. olivaceus population in Sendai Bay has both temporal and spatial structure. The temporal structure may be caused by variation in the timing of migration from the nursery to the deep offshore area in juveniles, and the spatial structure may be explained by individual variation in habitat preferences.

The present study aims to clarify the Seasonal bathymetric distributions of three coastal flatfishes (stone flounder, marbled flounder, and Japanese flounder) that are caught mainly by bottom trawls and gillnets off the coast of Fukushima, Japan, by using logbook data. All three species were found to have specific spawning depths, i.e., depths of 40–80 m, 20–40 m, and 10–60 m for stone, marbled, and Japanese flounders, respectively, with extremely high catch-per-unit-effort during their spawning seasons, reflecting spawning ground formation. Furthermore, Japanese flounder showed a tendency to expand their distribution offshore to depths deeper than 100 m after October. These results indicate interspecific variations in migration and aggregation patterns. Using logbook data and considering the seasonal catchability of each fishing gear enabled us to understand the seasonal bathymetric distribution of each species and the depths of their spawning grounds.

To determine the effects of the tsunami on kelp bed communities, we examined two kelp beds that had been surveyed before 2011 on the Pacific coast of Honshu Island, Japan. One survey was conducted in Tomarihama on the Oshika Peninsula, which is dominated by the large perennial brown alga Eisenia bicyclis, and the other survey was conducted in Nagane in Otsuchi Bay, where the large annual brown alga Saccharina japonica var. religiosa dominates. In Tomarihama, the tsunami was associated with a limited loss of E. bicyclis individuals. In contrast, the population of sea urchins, the primary herbivore occurring at high densities, drastically decreased after the earthquake, and a large occurrence of juvenile E. bicyclis was then observed over a broader depth range owing to the decrease in grazing pressure. Some of these juveniles survived to adulthood, and with survival over this extended depth range, the E. bicyclis bed expanded to deeper areas. In Nagane, the biomass of S. japonica var. religiosa displayed no significant change before and after the earthquake. A definite reduction in sea urchins was not observed after the earthquake. Thus, the impact of the earthquake and tsunami widely differed between Tomarihama and Nagane.

Off Fukushima, Japanese flounder (Paralichthys olivaceus) is a highly-valued species supporting coastal and offshore fisheries. We developed an age-structured population model incorporating seasonal coastal-offshore migrations to estimate and predict the abundance of Japanese flounder off Fukushima, where fishing has been restricted since the 2011 Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. We estimated the abundance of Japanese flounder using catch per unit effort from coastal gill net and offshore bottom trawl fishing from January 2000 to February 2011 and predicted the abundance under two different fishing effort scenarios (the same effort level as 2010 or decreased effort after the FNPP accident). Estimated abundance reflected the seasonal coastal-offshore migrations well, and it was estimated that abundance increased during and after 2007 because of high recruitments. In contrast, it was concluded that the predicted abundance on and after 2012 increased owing to the decreased fishing effort because the same estimated recruits were used in both scenarios. This indicates that the waters off Fukushima have effectively been serving as a marine protected area for Japanese flounder since the FNPP accident. This result was validated because almost all (83%) of the observed abundance index values calculated from a scientific bottom trawl survey during 2003–2014 were included within the estimated (predicted) 95% credible intervals of estimated (predicted) abundance index in the period. We also demonstrated the model's applicability for estimating the optimal fishing effort and age at first landing to maximize the earnings from gillnet and bottom trawl fisheries.

Drifting gill-nets were for a long time the main research gear for investigating the distribution of Pacific saury Cololabis saira. However, it has proven to be difficult to estimate the absolute abundance of saury using drifting gill-nets due to a lack of knowledge on the survey areas swept by these gill-nets. A mid-water trawl stock abundance estimation has the advantage of being able to estimate the absolute stock abundance before the commercial fishing season begins, whereas the conventional stock abundance estimation based on catch per unit efforts of commercial fisheries must be done after the commercial fishing season has ended. To confirm the practicality of a mid-water trawl to estimate the stock abundance of saury, we conducted a comparative survey in the northwestern Pacific Ocean using both a mid-water trawl and drifting gill-nets. We found that the geographic distribution pattern of catch per unit effort for both the mid-water trawl and driftnets was similar. Using the area-swept method and data on the fishing efficiency of the mid-water trawl obtained in a previous study, we were able to estimate the stock abundance plus confidence limits within the research areas. Our results suggest that the size composition of saury sampled by the mid-water trawl can be considered to approximate the actual size composition of saury.

Isotopic compositions of animal tissue are an intrinsic marker commonly used to trace animal origins and migrations; however, few isotopes are effective for this purpose in marine environments, especially on a local scale. The isotope ratio of the lanthanoid element neodymium (Nd) is a promising tracer for coastal animal migrations. Neodymium derives from the same geologic materials as strontium, well known as an isotopic tracer (87Sr/86Sr) for terrestrial and anadromous animals. The advantage of the Nd isotope ratio (143Nd/144Nd, expressed as εNd) is that it varies greatly in the ocean according to the geology of the neighboring continents, whereas oceanic 87Sr/86Sr is highly uniform. This study explored the utility of the Nd isotope ratio as a marine tracer by investigating the variation of εNd preserved in tissues of coastal species, and the causes of that variation, in a region of northeastern Japan where the bedrock geology is highly variable. We measured εNd and 87Sr/86Sr in seawater, river water, and soft tissues of sedentary suspension feeders: the mussels Mytilus galloprovincialis and Mytilus coruscus and the oyster Crassostrea gigas. We also measured concentrations of three lanthanoids (La, Ce, and Pr) in shellfish bodies to determine whether the Nd in shellfish tissue was derived from solution in seawater or from suspended particulates. The εNd values in shellfish tissue varied regionally (−6 to +1), matching the ambient seawater, whereas all 87Sr/86Sr values were homogeneous and typical of seawater (0.7091–0.7092). The seawater εNd values were in turn correlated with those in the adjacent rivers, linking shellfish εNd to the geology of river catchments. The depletion of Ce compared to La and Pr (negative Ce anomaly) suggested that the Nd in shellfish was derived from the dissolved phase in seawater. Our results indicate that the distinct Nd isotope ratio derived from local geology is imprinted, through seawater, on the soft tissues of shellfish. This result underscores the potential of εNd as a tracer of coastal marine animals.

In the original publication, Fig. 1 and legend have been incorrectly published. The correct version of Fig. 1 and legend are provided in this Correction.

Ontogenetic habitat shift and feeding habits in the shallow (

Vertical swimming events (VSEs) of the Japanese flounder, Paralichthys olivaceus, recorded by high-frequency depth data loggers, were analysed to identify spawning events. In total 25,907 VSEs from 10 adult fish were classified into 4 clusters using a k-means method. VSEs in a specific cluster (cluster-S) characterised by accelerated vertical swimming were identified as possible spawning events. Both the descent (0.43 ± 0.22 body length s− 1) and ascent rates (0.43 ± 0.24 body length s− 1) of VSEs in cluster-S were more than 4 times faster than in any other VSE. Our analyses indicated that 4 individuals exhibited the spawning events during the recording periods. The estimated spawning frequency ranged from 0.74 to 0.90 events day− 1. These values were comparable to those obtained in other field and laboratory studies. The spawning condition of fish at the time of recapture was confirmed by separate histological and anatomical observations, which supported the cluster analysis results. These results suggest that a clustering technique can be successfully applied to identify spawning behaviour from time-depth data of free-swimming flatfishes that exhibit vertical swimming movements., Journal of Sea Research, 75, pp.33-40; 2013

A generalized method to accurately estimate the spawning fraction (S) of multiple batch spawning fish considering the duration of histological spawning markers over a wide range of ambient temperature, spawning time frequency distribution of the population, and sampling time was developed. The concept of the variable “fraction of the daily spawning females with spawning markers at a sampling time t (FDSMt)”, which varies diurnally in relation to the duration of the spawning markers and the spawning time frequency distribution, was introduced. Spawning fraction can be calculated as S = Psmt × (1/FDSMt), where Psmt is the observed fraction of active females with signs of previous or imminent spawnings, referring to various spawning markers, at a sampling time t. Simulations suggested the following two methods were robust when the spawning time frequency distribution was long and uncertain. The first refers to sampling females evenly throughout the 24 h period, whilst the second is based on selecting a single or combination of spawning markers so that the total temperature-adjusted marker duration at sampling sums to around 24 h and applying, if necessary, a correction factor. With these methods, the influence of sampling time and spawning time frequency distribution can be ignored. The utility of the second method was evaluated with field data for Japanese flounder Paralichthys olivaceus. In all cases, accurate validation of the temperature-dependent duration of spawning markers is essential for accurate estimation of S.

We investigated the diet and somatic condition of 5129 individual Japanese flounder Paralichthys olivaceus, 20 to 92 cm in total length, in the Joban area along the Pacific coast of Japan (36° 40' N to 38° 00' N) from 2001 to 2007. Japanese flounder with food in their stomachs (1668 indi- viduals) consumed chiefly fishes (92% of stomach contents by weight). Predominant prey species were Japanese anchovy Engraulis japonica (54% of fishes by weight) and Japanese sandlance Ammodytes personatus (22%). Japanese anchovy were consumed by Japanese flounder year round except in March and April, when the anchovy migrate from the Joban area. In March and April, Japanese flounder frequently consumed Japanese sandlance, but only in the northern part of the Joban area (37° 20' N to 38° 00' N); Japanese flounder did not feed on this species and had less con- tent in their stomachs in the southern area (36° 40' N to 37° 20' N), where the sandlance is absent. Somatic and hepatosomatic conditions of Japanese flounder in the northern area were better than those in the southern area in March and April, suggesting that such spatial and seasonal hetero- geneities in prey availability affect the nutritional status of predators.

Larvae of bigmouth manefish Caristius macropus are described and illustrated on the basis of seven specimens (4.2-10.5 mm in body length) from the Kuroshio waters (0-60 m depth) and the transition waters (surface) between the Kuroshio and Oyashio fronts of the western North Pacific. The present larvae of C. macropus are distinguished from those of Paracaristius maderensis that inhabit the North Pacific by having 39-40 myomeres, 34 dorsal-fin rays, and 22 anal-fin rays. The present study, along with previous studies of the early life stages of caristiids, shows that larvae of the family may be defined by the following characters: body elongate in preflexion stage but becoming deep bodied and hatchet shaped after notochord flexion; anus located near vertical through base of pectoral fin; head large, without spination or serration; a distinct vertical band on the posterior tail throughout the larval stages, and two bands gradually appearing on the tail and trunk during the flexion and postflexion stages; and melanophores present around the notochord tip by the flexion stage. Adult C. macropus are found in the subarctic and temperate waters of the North Pacific; however, the present study and other occurrences of early life stages of the species probably indicate that C. macropus may spawn over a wide area in the North Pacific.

We examined the relative importance of growth-related processes operating during the larval and early juvenile stage in explaining variability in year class success of Japanese flounder off the Pacific coast of northern Japan. Early growth trajectory of larvae and juveniles sampled in 2005 (strong year class) and in 2006 (weak year class) was estimated from the analysis of the lapillar otolith. The larval pelagic stage was characterized by lower growth and developmental rates, as well as high selection for fast growth in the metamorphosis/settlement period, during the strong recruitment event of 2005 relative to 2006. Growth appeared higher in 2005 only after settlement despite high density in the nursery, which likely reflected superior productivity during that year combined with an increased probability of cannibalism from early settlers on late settlers. This implies that larval growth dynamics did not play an important role in determining recruitment strength in the two years considered. The decreasing distance from the nursery areas of pelagic larvae through ontogeny in 2005, combined with low age at settlement, suggest that larvae benefited from positive transport conditions during the dominant year class. To the contrary, unfavorable hydrographic conditions likely prevailed in 2006 as distance from the nurseries increased with ontogeny and settlement occurred later than in 2005 despite faster growth potential and developmental rate. We conclude that transport conditions to the nursery grounds, rather than larval growth potential, represented the most important determinant of year class success in the two years considered.

Early cycle oocyte recruitment has previously been described and partly quantified in teleosts with a determinate reproductive style. This recruitment is, however, less understood in indeterminate fish due to additional factors further complicating quantification by traditional means. These factors include the extremely broad size range of oocytes, where gap formation between previtellogenic and vitellogenic oocytes cannot be identified, an important number of previtellogenic oocytes close to the threshold of vitellogenesis, and a lack of knowledge of the importance of atresia during vitellogenesis. These problems were largely solved by combining advanced packing density theory and stereological measurements aided by image analysis, which allowed for a much better understanding of the early cycle oocyte recruitment pattern in European hake ( Merluccius merluccius ). This novel type of analysis demonstrated that the European hake presents a continuous , indeterminate fecundity style in which the steady recruitment of oocytes from the large pool of previtellogenic oocytes (about 500,000 g −1 at the perinucleolar stage) leads to multiple vitellogenic cycles during the extensive reproductive season.

For ectothermic fish, water temperature may influence the timing and location of reproduction. The water temperature in semi-enclosed bays fluctuates substantially compared to the neighbouring open sea, leading to thermal differences between the bay and the open sea. This phenomenon may stimulate the habitat shifts of seasonally migratory fish. To clarify the effects of temperature on the habitat shifts, we used depth-temperature data loggers to monitor the behaviour of adult Japanese flounder Paralichthys olivaceus (range: 47.0–57.6 cm) in Omura Bay, a typical semi-enclosed bay in Japan. Ten flounder were tagged and released in December, 2007. A total of six loggers and four tagged fish were recovered; two loggers and one tagged fish were retrieved from the Omura Bay, and four loggers and three tagged fish from the East China Sea. The variations in temperature and harmonic constants of the M 2 tide extracted from the data logger showed that the emigration of three of the six fish from the bay to the open sea corresponded with the rise in temperature experienced by the fish. The water temperature in the bay continuously decreased and finally fell below the lower threshold of the optimal temperature for hatching of their eggs. Anatomical observations conducted on four individuals recaptured outside the bay revealed the presence of post-ovulatory follicles and/or oocytes at the maturing stage, indicating that they were spawning in the open sea at the time. Vertical swimming activity of the fish was significantly increased after the emigration from the bay, suggesting that spawning, foraging, and movement opportunities were increased. Therefore, it appears that adult Japanese flounder shift their habitats during the reproductive period to find higher temperatures that offer physiological and ecological advantages.

This paper explores why the ‘Auto-diametric method’, currently used in many laboratories to quickly estimate fish fecundity, works well on marine species with a determinate reproductive style but much less so on species with an indeterminate reproductive style. Algorithms describing links between potentially important explanatory variables to estimate fecundity were first established, and these were followed by practical observations in order to validate the method under two extreme situations: 1) straightforward fecundity estimation in a determinate, single-batch spawner: Atlantic herring (AH) Clupea harengus and 2) challenging fecundity estimation in an indeterminate, multiple-batch spawner: Japanese flounder (JF) Paralichthys olivaceus . The Auto-diametric method relies on the successful prediction of the number of vitellogenic oocytes (VTO) per gram ovary (oocyte packing density; OPD) from the mean VTO diameter. Theoretically, OPD could be reproduced by the following four variables; OD V (volume-based mean VTO diameter, which deviates from arithmetic mean VTO diameter), VFvto (volume fraction of VTO in the ovary), ρ o (specific gravity of the ovary) and k (VTO shape, i.e. ratio of long and short oocyte axes). VF vto , ρ o and k were tested in relation to growth in OD V . The dynamic range throughout maturation was clearly highest in VF vto . As a result, OPD was mainly influenced by OD V and secondly by VFvto. Log (OPD) for AH decreased as log (OD V ) increased, while log (OPD) for JF first increased during early vitellogenesis, then decreased during late vitellogenesis and spawning as log (OD V ) increased. These linear regressions thus behaved statistically differently between species, and associated residuals fluctuated more for JF than for AH. We conclude that the OPD-OD V relationship may be better expressed by several curves that cover different parts of the maturation cycle rather than by one curve that cover all these parts. This seems to be particularly true for indeterminate spawners. A correction factor for vitellogenic atresia was included based on the level of atresia and the size of atretic oocytes in relation to normal oocytes finding that OPD would be biased when smaller atretic oocytes are present but not accounted for. Furthermore, special care should be taken when collecting sub-samples to make them as representative as possible of the whole ovary, including in terms of relative amount of ovarian wall and stroma. Theoretical consideration, along with original, high-quality information regarding the above-listed variables made it possible to reproduce very accurately the observed changes in OPD, but not yet precisely enough at the individual level in indeterminate spawners.

The role of gonadotropin (GTH) in the reproduction of the Japanese flounder, Paralichthys olivaceus, was studied by assessing the changes in the apparent activity of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland during gonadal maturation by immunohistochemical analyses. Corresponding changes in plasma levels of testosterone (T), estradiol-17beta (E(2)), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) were also studied. Reared fish at the early spawning to termination stages were sampled from May to August and wild fish at the previtellogenic to termination stages were caught at 3- to 4-week intervals between April and September offshore from the northern mainland of Japan by gill nets. The gonadosomatic index of the reared fish decreased from the early spawning stage to the termination stage, while that of the wild fish increased significantly from the previtellogenic stage to the early spawning stage and decreased thereafter. In the reared fish, the immunostaining intensities of FSH and LH were high during the spawning period, accompanied by high plasma levels of T, E(2), and DHP. In the wild fish, the immunostaining intensities of FSH and LH were low during the previtellogenic stage but increased during the maturing and spawning stages. These results indicate that both FSH and LH are likely associated with oocyte maturation in the Japanese flounder.

To clarify the possible roles of gonadotropin-releasing hormone (GnRH) in the reproduction of Japanese flounder Paralichthys olivaceus, localization of salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II), and sea bream GnRH (sbGnRH) immunoreactive (ir) cell bodies and fibers in the brain and pituitary were examined together with follicle stimulating hormone (FSH) and luteinizing hormone (LH)-ir cells in the pituitary by immunohistochemistry. sGnRH-ir cell bodies were localized in the ventromedial part of the rostral olfactory bulb and cGnRH-II-ir cell bodies were restricted to the midbrain tegmentum, while sbGnRH-ir cell bodies were evident in the preoptic area. sGnRH-ir fibers were distributed throughout the brain, especially abundant in the forebrain. cGnRH-II-ir fibers were also scattered in many areas of the brain with abundance in the midbrain, but sbGnRH-ir fibers were observed in the preoptic-hypothalamic area and innervated the pituitary. In the pituitary, neither sGnRH-ir fibers nor cGnRH-II-ir fibers were found, but sbGnRH-ir fibers were profuse in the neurohypophysis and invaded the proximal pars distalis, targeting FSH and LH cells. These results suggest that three GnRH systems can play different physiological roles in the brain of Japanese flounder. Among them, sbGnRH is considered to be involved in reproduction by stimulating gonadotropin secretion, while sGnRH and cGnRH-II can function as a neurotransmitter and/or neuromodulator within the brain in this species.

This study examined age and growth of Japanese flounder Paralichthys olivaceus off the Pacific coast of northern Japan, and determined whether the growth patterns of male and female fish in northern (40–41°N) and southern (37–38°15′N) waters differ. In total 8095 specimens were collected between January 1999 and December 2005. Zonation consisting of opaque and translucent bands on the otolith was evident. Within each opaque band a thin and clear check (ring mark) was observed in all specimens examined. Monthly change in the frequency of appearance of a ring mark on the outer margin of the otolith indicates that ring marks form between July and August. The von Bertalanffy growth model showed a sexual dimorphism in growth, as females grew faster and reached a larger size than males. The growth patterns obtained by tracking the observed total length for monthly collections showed a rapid increase in total length between August and October. Spatial variation in the growth pattern of male and female fish between northern and southern waters was evident, as southern fish were significantly larger than northern counterparts during 1.25–3.00 years post hatch.

To elucidate the interannual response of Pacific saury growth to climate variability, a simple 3-box model of NEMURO.FISH was forced by observed sea surface temperature (SST) from 1950 to 2002. In the model, fish wet weight is calculated according to a fish bioenergetics equation. The observed condition factor of Pacific saury showed large decadal variability with significant year-to-year variability. In the model, wet weight of Pacific saury also showed decadal and year-to-year variability, however the amplitude of decadal variability was much smaller than observed. The cause of the model failure is suggested to be the absence of a multi-species fish formulation in the model. The Japanese sardine population, which has a large biomass that exhibits great decadal fluctuations, is proposed as potentially affecting zooplankton density in the saury migration region. We also investigated differences of interannual growth variability between spawning seasons. Since Pacific saury spawns from autumn to the following spring, we consider three seasonal (autumn, winter and spring) cohorts in the model. The amplitude of growth variability is largest for the spring-spawned cohort and smallest in the winter-spawned cohort. This difference is caused by the difference of life history of each spawned cohort. The spring-spawned cohort spawns only once in their life-cycle, however other cohorts spawn twice. During the (autumn) fishery season, age 1 spring-spawned cohort has not yet spawned, while the other cohorts have spawned once. As a result, the spring-spawned cohorts retain the memory of the environmental influence during the early life stages while the other cohorts, through their spawning, have erased that memory. Hence, the spring-spawned cohort shows a larger fluctuation in wet weight than other cohorts.

NEMURO.FISH was applied to Pacific saury to study the dependence of spawning season on growth. The model was composed of three ocean domains, which corresponded to the Kuroshio, the Oyashio, and the interfrontal zone (mixed water) regions. In these three domains, a lower trophic model (NEMURO) was coupled with a simple physical model, and the time-variation of three zooplankton size classes was input as prey densities into the saury bioenergetics model. Three numerical experiments were examined using this model, which corresponded to three different spawning seasons. Results showed that in the first year winter-spawned saury showed the fastest growth, and spring-spawned showed the slowest growth, while in the second year (time to grow to 120 g wet weight), the reverse occurred, i.e., spring-spawned saury showed the fastest growth. This difference in growth, which depends on the spawning season, can explain the bimodal size distribution of early autumn catch data.

We examined the relationship between body size and maturation in male Japanese flounder Paralichthys olivaceus , and whether spatial variation in the occurrence of mature fish between southern (Fukushima and Miyagi prefectures, 38° N) and northern (Aomori Prefecture, 41° N) waters could be explained by variation in growth rates and somatic body condition. Male flounder in southern and northern waters matured sexually at two years of age; however, the probability of 2-y-old males being mature differed between the two waters. In southern waters, almost all 2-y-old males had mature testes during the spawning season (May–September), whereas the majority of 2-y-old males in northern waters remained immature during the same period. Males in southern waters had grown faster than those in northern waters by summer, two years after birth, but the length range of males in the two regions largely overlapped during the spawning season. The somatic condition of 2-y-old males in June was significantly higher in southern waters than in northern waters, but there was no significant difference in condition between immature and mature specimens in each region. The length-growth increments of 2-y-old males in southern waters during the growing season, just after the spawning season, were similar to those in northern waters. These discrepancies in fish between northern and southern waters did not appear to be explained by the theory of growth and energy allocation strategies. Our findings show that life-history traits of male Japanese flounder may vary on a small geographical scale off the Pacific coast of northern Japan.

Objective: We examined whether interstitial cells (ICs) of the human urinary bladder expressed β-adrenoceptor (AR) subtypes, and semiquantitatively compared the staining intensity among urothelium, ICs and detrusor muscles. Methods: Paraffin sections of the human urinary bladder were obtained from histologically normal areas of formalin-fixed specimens removed for bladder carcinoma. Double-labeling immunohistochemical methods using antibodies against each β-AR subtype and vimentin were performed to identify ICs of the human urinary bladder. The staining intensity of β-ARs was semiquantitatively compared among urothelium, ICs and detrusor muscles. Further, gender-related difference or age-related correlation in the staining intensity of β-ARs was compared in the same cell types. Results: The expression of β1-, β2-, and β3-AR was observed in vimentin-positive ICs localized in suburothelium, between detrusor muscle bundles, and within these bundles of the human urinary bladder. The rank order of the staining intensity was urothelium > ICs = detrusor muscles in β1-AR, urothelium > ICs > detrusor muscles in β2-AR, whereas its order was ICs = detrusor muscles > urothelium in β3-AR. Except for urothelial β1-AR, there was no gender-related difference in the signal intensity of β-ARs in the urothelium, ICs or detrusor muscles. Age negatively correlated with the signal intensity of all β-AR subtypes. Conclusion:β-ARs were expressed in vimentin-positive ICs of the human urinary bladder. As for β2- and β3-AR, there was no gender-related difference or age-related correlation in urothelium, ICs and detrusor muscles. In the human urinary bladder, β-ARs expressed in ICs may play a role in bladder physiology.

We examined year-class-related differences in radiocesium concentrations in Pacific cod (Gadus macrocephalus) and evaluated the potential factors affecting the differences after the release of large amounts of radionuclides from Fukushima Dai-ichi Nuclear Power Plant (FNPP) in March 2011. The concentration of radiocesium was highest in the 2009 and earlier year-classes (yc) (≤2009 yc), followed by the 2010 yc, and was rarely detected in the 2011 yc. Trawl surveys throughout the year revealed that a proportion of Pacific cod born in or before 2009 and 2010 were distributed in the coastal area from winter to early summer, whereas all individuals were on the upper continental slope from early summer to winter. The concentration of radiocesium decreased more rapidly in the 2010 yc than in the ≤2009 yc. The diet of cod changed ontogenetically and spatiotemporally. The organisms preyed upon on the upper continental slope by cod of all year-classes and in the coastal area by the 2010 yc contained very low concentrations of radiocesium. However, some food items ingested in the coastal area by the ≤2009 yc had relatively high radiocesium levels. These results suggest that Pacific cod primarily accumulated radiocesium during the first few months after the FNPP accident. Age- and body size-dependent differences in growth, metabolic rate, and diet, as well as seasonal migration patterns, also affected the rate of decrease in radiocesium levels, which likely led to the differences we observed between year-classes.

Radiocesium (Cs) contamination histories of the Japanese flounder, Paralichthys olivaceus, after the 2011 Fukushima Nuclear Power Plant (FNPP) accident were examined by analysis of the spatiotemporal changes in observed Cs concentrations, by comparison of the dynamics of the Cs concentrations in several year-classes of fish, and by simulation studies. Two contamination histories were revealed: (1) severe contamination by water that was directly released from the FNPP with extremely high Cs concentrations for a few months after the accident, which had a highly variable spatial distribution; and (2) long-duration contamination at relatively low concentrations resulting from consumption of contaminated food. These two histories were supported by three observations. First, high Cs concentrations with high variability were observed in the first year after the accident. Second, the highest values of the minimum Cs concentrations were observed in the autumn of 2011. Third, Cs concentrations were lower with smaller variation for fish from the 2011 year-class and younger, which were not exposed to the highly contaminated directly released water, than for fish from the 2010 year-class and older. Simulation studies also indicated that the Cs concentrations in some individuals that were exposed to the directly released water might not be in an equilibrium state even at 3 years after the accident. On the basis of these contamination histories, it can be expected that the Cs concentrations in most Japanese flounder will continue to decrease.

To elucidate the role of gonadotropin-releasing hormone (GnRH) in gonadal maturation in wild female Japanese flounder Paralichthys olivaceus, we monitored changes in the levels of seabream GnRH (sbGnRH) in the olfactory bulb, telencephalon, hypothalamus, and pituitary during ovarian development together with changes in plasma levels of testosterone (T), estradiol-17β (E2), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP). Fish were caught offshore of the northern mainland of Japan in the Pacific Ocean at 3- to 4-week intervals between April and September by gill net. The netted fish were categorized into six groups based on ovarian stages: previtellogenic (April–early May), early yolk (April–late May), late yolk (late May–June), early spawning (June–August), late spawning (September), and termination (September) stages. The gonadosomatic index significantly increased from the previtellogenic to early spawning stages and decreased thereafter. In the olfactory bulb, no significant differences were observed in sbGnRH levels among the developmental stages. In contrast, sbGnRH levels in the telencephalon and hypothalamus were very high in the previtellogenic stage, lower in the early spawning stage, and relatively high in latter stages. sbGnRH levels in the pituitary were high in the previtellogenic stage and low in the early spawning stage. In addition, the relatively high levels of pituitary sbGnRH were found together with high plasma T, E2, and DHP levels in fish in the late yolk stage. These results indicate that sbGnRH in the telencephalon, hypothalamus, and pituitary is involved in ovarian maturation and that sbGnRH may play an important role in the initiation of ovarian recrudescence in wild Japanese flounder.

The ages (n=11 178) and length frequency distributions (n=173 300) of Pacific saury Cololabis saira caught from September to November in 1989–2000 were examined. Most specimens were determined as either age 0 or 1 based on the number of annual rings in the otolith. The knob lengths (length from the tip of the lower jaw to the posterior end of the muscular knob on the caudal peduncle) at which 50% of the fish were age 1 ranged 277.8–304.7 mm. Analysis of length frequency distribution was also useful to divide the knob lengths of the two groups. The modal lengths of age 1 fish ranged 303.9–325.9 mm.

The spatial distribution of Todarodes pacificus in and near the Kuroshio/Oyashio Transition Zone during its northward migration was examined by comparative surveys using two types of mid-water trawl net and supplementary squid jigging from June to July 2000. The vertical and horizontal distribution patterns varied for different body sizes in relation to the oceanographic structure. Todarodes pacificus of 1–20 cm dorsal mantle length (ML) were widely distributed from the coastal waters of Japan to near 162°E longitude, probably due to transport by the Kuroshio Extension (KE). Todarodes pacificus smaller than 10 cm ML were mainly distributed in temperate surface layers at sea surface temperatures (SSTs) >15°C near the KE meander probably because of their poor tolerance to lower temperatures and limited swimming ability. Squid of 10–15 cm ML were distributed in the offshore waters of 10–15°C SST and in the coastal waters of northern Honshu, and underwent diel vertical migrations between the sea surface at night and deeper layers during the daytime. Squid larger than 15 cm ML were distributed in the coastal feeding grounds of northern Honshu and Hokkaido until they began their southward spawning migration. They also underwent diel vertical migrations, but remained deeper at night than the squid of 10–15 cm ML; this migration pattern closely matched that of their main prey such as euphausiids. We concluded that as T. pacificus grow, they shift their distribution range from the temperate surface layer around the KE toward the colder deeper layers, above 5°C, in the Oyashio and coastal areas.

Wild a dult maturing and immature female Japanese flounder Paralichthys olivaceus were collected in June 2004 and January 2005, respectively, to clarify a possible role of gonadotropin-releasing hormones (GnRHs) in reproduction. Levels of salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and sea bream GnRH (sbGnRH) in the brain and pituitary were examined by time-resolved fluoroimmunoassay. Three forms of GnRHs were detected in the discrete brain at various levels. In the pituitary of both maturing and immature fish, sbGnRH was abundant together with a pronounced amount of sGnRH, whereas cGnRH-II was almost below the detectable limit. In maturing fish, levels of sbGnRH were high in the telencephalon, hypothalamus and pituitary, while levels of sbGnRH of immature fish were very low in these regions. These results indicate that sbGnRH is mainly responsible for gonadotropin secretion, and that sb GnRH in the anterior part of the brain is associated with gonadal maturation in the Japanese flounder.

Seasonal and diel variation of feeding activities of Pacific saury (Cololabis saira) were examined following their annual migration cycle in North Pacific waters adjacent to Japan in relation to oceanographic conditions, especially abundance and composition of zooplankton collected in surrounding waters. A high gut fullness and low degree of digestion of the gut contents were frequently observed during the dusk period during the 24-h cycle for all seasons. In spring and summer saury were distributed in the Kuroshio–Oyashio transitional region and the Oyashio (cold current) area, where they mainly fed on the euphausiid, Euphausia pacifica, and had a higher gut fullness than the other seasons. Their feeding activity decreased in fall, and increased in winter, the spawning season, although they were distributed in an area of poor food conditions in the Kuroshio warm current area. Their distribution in the Kuroshio–Oyashio transitional region and the Oyashio area allow utilization of adult euphausiids, E. pacifica which is a significant food source.