Reiji Masuda

Kyoto University, Kioto, Kyōto, Japan

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Publications (96)119.67 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: Many euryhaline wanderer species exhibit seasonal habitat changes, and temperature is suggested to play a key role in this phenomenon. To examine this possibility, we tested the hypothesis that adaptable temperature ranges of euryhaline wanderers are narrower in a non-natal osmotic environment than in their natal osmotic environment using dace Tribolodon hakonensis, a freshwater born euryhaline fish, and black porgy Acanthopagrus schlegelii, a marine born euryhaline fish. In both species, all individuals survived for 48 h in all the tested temperatures in their natal osmotic environments. In non-natal osmotic environments, however, both low (dace: 6 °C, black porgy: 10 °C) and high temperatures (dace: 30 °C, black porgy: 33 °C) significantly reduced their survival. These results indicate that euryhaline wanderers have a narrowed adaptable temperature range in non-natal osmotic environments. The similar trend observed in these two species of freshwater and marine fishes suggests that this may be a general characteristic in euryhaline wanderers and could be one of the causes of their seasonal movements.
    Full-text · Article · Jan 2016 · Fisheries Science
  • Mai Yamaguchi · Reiji Masuda · Yoh Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: We examined the diel activity pattern of the sea cucumber Apostichopus japonicus with or without the presence of food and predators. We also tested whether they have the capability for time–place learning. In the feeding experiment, juvenile and adult sea cucumbers were fed at either 00:00 or 12:00, at a fixed feeding place for 12 days, and the presence of animals in the feeding area was recorded. In the predator experiment, juvenile sea cucumbers were kept in a tank with or without a filefish, and the emergence of juvenile sea cucumbers outside the oyster shell area was recorded. Juvenile sea cucumbers did not show a diel activity rhythm, whereas adults were nocturnal, but this was altered by feeding at 12:00. Neither juveniles nor adults appeared in the feeding area before feeding time, suggesting an inability for time–place learning. Juvenile sea cucumbers hid under the oyster shells during the daytime and were active at night in the presence of a filefish, but without a filefish, they also showed high activity in the daytime. We suggest that sea cucumbers change their activity depending on the presence of food and predators, but without the influence of time–place learning.
    No preview · Article · Nov 2015 · Fisheries Science
  • Hirona Makino · Reiji Masuda · Masaru Tanaka
    [Show abstract] [Hide abstract] ABSTRACT: Hatchery-reared fish often show different behavioral traits from their wild counterparts, possibly due to the lack of environmental stimuli. Here, we aimed to reveal the stage-specific effect of environmental stimuli on the development of learning capability in striped knifejaw Oplegnathus fasciatus. The fish were raised for 15 days (50–65 days post-hatch) or 30 days (50–80 or 90–120 days post-hatch) in either conventional rearing tanks (control) or in a structurally enriched tank containing bricks, artificial sea grass, and plastic pipes (enriched environment), and were examined for learning capability using Y-maze reward conditioning. The learning capability of wild juveniles was also examined, and their scores were compared with those of hatchery-reared fish (which we previously reported). Only fish in the 50–80 days post-hatch enriched-rearing group showed significantly better scores than those in the control group, and wild fish performed better than hatchery-reared ones. The present results indicate that, although the learning capability of hatchery-reared fish is inferior to that of wild fish, exposure to a highly structured environment at an appropriate stage promotes the development of learning capability. Such environmental enrichment can potentially improve the viability of hatchery-reared fish when they are released into the wild.
    No preview · Article · Sep 2015 · Fisheries Science
  • [Show abstract] [Hide abstract] ABSTRACT: We conducted a 30-day feeding experiment on threadsail filefish Stephanolepis cirrhifer to evaluate the efficacy of giant jellyfish Nemopilema nomurai on the growth and body composition of the filefish. Four treatments were prepared: starved (control, S), fed only jellyfish (J), fed only pellets (control, P), and fed both jellyfish and pellets (JP). Threadsail filefish consumed the giant jellyfish as much as 5.6 and 4.1 times their own body weight per day in the J and JP treatments, respectively. Fish in the S treatment had 68% mortality, whereas the J treatment had no mortality. Fish in the JP treatments showed significantly faster growth than those in the P treatment. The giant jellyfish contained a high ratio of n-6 highly unsaturated fatty acids, especially arachidonic acid as well as free amino acids, especially taurine. The high contents of these acids refoected those of fish body composition. These results showed that feeding giant jellyfish for threadsail filefish improved their growth and body composition, and we therefore recommend the use of jellyfish as supplemental feed for stock enhancement or aquaculture.
    No preview · Article · Jul 2015 · NIPPON SUISAN GAKKAISHI
  • Kohji Takahashi · Reiji Masuda · Yoh Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: The present study investigated whether red sea bream Pagrus major could learn about feeding and avoidance area through video model observation. In Experiment 1, 45-mm standard length (SL) fish were trained to learn about a feeding area in a tank. In Experiment 2, 114-mm SL juveniles were trained to avoid a hand net by moving into a shelter. Three treatments were established in each experiment: (i) live model observer: fish observed the behavior of a real fish in an adjacent tank; (ii) video model observer: fish observed video playback of a conspecific on a monitor; and (iii) non-observing control. Ten observational trials were performed in both experiments for the live and video model observer. Afterwards, fish from all treatments were conditioned by feed or avoidance training. In Experiment 1, there was no difference in the feed learning process among treatments. In contrast, in Experiment 2, live and video model observers acquired avoidance learning more quickly than control. The result indicates that the video model can be as efficient as the live model for observational learning in fish. This study suggests that video playback may be useful for anti-predator training of seedlings for stock enhancement.
    No preview · Article · May 2015 · Fisheries Science
  • [Show abstract] [Hide abstract] ABSTRACT: Measurement of the magnetic hyperfine fields in metallic thin wires under spin Hall conditions was attempted using the emerging technique, synchrotron-radiation Mössbauer spectroscopy. A Mössbauer probe layer of 57Fe (0.2 nm), 57Fe (0.6 nm), or 119Sn (0.6 nm) was embedded as an electron spin detector near the surfaces of V, Au, Pt, and 56Fe wires. The magnitudes of the magnetic hyperfine fields at the 57Fe and 119Sn nuclear sites that could be enhanced by non-equilibrium conduction-electron spin polarization were measured both without and with the application of an electric current along the wire. Changes in the Mössbauer spectra were not clearly observed, indicating that the magnetic hyperfine field induced by non-equilibrium spin polarization is smaller than the detection limit at least for the measured systems and conditions.
    No preview · Article · May 2015 · Journal of Applied Physics
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    Li J · Haga Y · Masuda R · Takahashi K · Ohta H · Ishida S · Satoh S
    Full-text · Dataset · Apr 2015
  • Koji Tokuda · Reiji Masuda · Yoh Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: Conditional discrimination in the octopus (Octopus vulgaris) was studied using successive discrimination training. The experimental animals were divided into two groups, and a barrel-shaped white object (stimulus) was presented to each group. One of the groups was rewarded with food for responding to the stimulus, but only when the tank was aerated, whereas the other group was rewarded with food for responding to the stimulus when the aeration was switched off. The number of trials in which octopuses responded to the stimulus, and the latency of the responses, were significantly different between trials with the aeration on and trials with the aeration off, in both groups. Therefore, the octopuses learned to conditionally discriminate.
    No preview · Article · Jan 2015 · Journal of Ethology
  • [Show abstract] [Hide abstract] ABSTRACT: We evaluated the efficiency of feeding moon jellyfish Aurelia sp. to red sea bream Pagrus major by conducting nutritional and behavioral analyses. Four treatments were prepared in our 108-day feeding trial as follows: starved (S), fed only jellyfish (J), fed only pellets (P), and fed both jellyfish and pellets (JP). Juveniles consumed jellyfish as much as 5.3 and 1.3 times their own body weight per day in the J and JP treatments, respectively. Although there were no major contributions to the growth by feeding jellyfish, fish in the J treatment showed better survival, daily growth rate or condition factor than those in the S treatment. Fish in the JP treatments showed a significantly higher rate of exhibiting tilting (anti-predator) behavior than those in the P treatment. The latency to start tilting after the transference was significantly shorter, whereas the latency to start swimming was significant longer in the JP treatment than in the P treatment. We recommend the utilization of jellyfish as subsidiary prey for juvenile fish for stock enhancement.
    No preview · Article · Nov 2014 · NIPPON SUISAN GAKKAISHI
  • Reiji Masuda
    [Show abstract] [Hide abstract] ABSTRACT: A bi-monthly underwater visual census has been conducted in a temperate rocky reef habitat in Japan since January 2002. My previous paper revealed that fish assemblages from years 2002 to 2006 included more of southern species compared to those found in a survey conducted from 1970 to 1972. The present paper tests following hypotheses: 1) warm water species has increased for the recent 12 years, ii) interannual fluctuation of recruitment is dependent on the pelagic larval duration (PLD) in each species. A total of 95 fish species were recorded in this survey period, during which bottom water temperature ranged from 9.8 to 29.6 °C. Both species richness and fish abundance were high in summer and low in winter. Bottom water temperature gradually increased in this period coinciding with the increase of southern species. Interannual fluctuation was not necessarily dependent on the PLD. For example, jack mackerel with a long PLD and two species of goby with a short PLD had a low level of interannual fluctuation, whereas the recruitment of red sea bream with a medium PLD highly fluctuated in abundance.
    No preview · Conference Paper · Aug 2014
  • Yuichi Fukunishi · Reiji Masuda
    [Show abstract] [Hide abstract] ABSTRACT: The amount of UV-B radiation has increased due to depletion of the ozone layer. It is well documented that exposure to UV-B increases mortality in marine fish larvae. However, UV avoidance behavior of fish larvae has received little attention. Here we test the hypothesis that Japanese flounder larvae stay deeper in the water column to avoid UV-B radiation. A UV-B lamp was placed above a tank. A larva was released near the surface of the tank. The vertical position of the larva was observed by eye every 15 seconds for 15 minutes that consists of 5 minutes × 3 phases, pre UV exposure, UV exposure and post UV exposure. Control treatment without UV-B radiation was also set. Trials were replicated 8 times for each treatment. In pre UV exposure, larvae stayed shallower than 10 cm in both UV-B and control treatment and no significant difference was observed. In UV exposure and post UV exposure, the average depth of larvae in UV-B treatment was significantly more than that of control treatment. Present results indicate that Japanese flounder larvae actively avoid UV-B radiation. We suggest that UV avoidance behavior should be taken into account to access UV-induced mortality in marine fish larvae.
    No preview · Conference Paper · Aug 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Background/Question/Methods Given the current crisis of biodiversity loss, a quantitative biological assessment in natural ecosystems has become a matter of urgency. In particular, there are serious concerns regarding changes in fish communities in marine ecosystems because such changes would have significant impacts on ecosystem processes and the sustainability of fisheries. Recently, a research method for aquatic vertebrate assessment using environmental DNA (eDNA) has been developed and applied extensively in inland waters; however, only a few applications in the marine environment have been reported. Here, we conducted a fish survey in a marine coastal habitat using the eDNA technique. To evaluate the effect of temperature on the amount of DNA, eDNA was recovered from tanks in which juveniles of jack mackerel (Trachurus japonicus) were maintained under three temperature conditions. An analysis of eDNA was also conducted in tanks containing fish at four density levels. Subsequently, the fish community in the natural habitat was surveyed by SCUBA divers followed by eDNA analysis of sampled water. Nine surveys were performed along the coast of Maizuru Bay, Japan, from October 2012 to February 2013. TaqMan real-time PCR was performed targeting five fish species, and the results were compared with those of the visual census. Results/Conclusions eDNA was detected in all tanks containing jack mackerel. The amount of eDNA was not significantly different among the three temperature conditions examined (12, 20, or 28°C). This finding is essential knowledge for the establishment of a quantitative system in the field. The eDNA concentration in the tanks with different fish densities (0, 3, 10, or 30 individuals of fish in a 500-liter tank) did not reflect the fish density in the tanks due to the high variation in eDNA in the low density tanks. The underwater visual census recorded a total of approximately 3,000 fish belonging 36 species. The eDNA density/detection frequency corresponded reasonably well with the fish abundance recorded in the underwater visual census for jack mackerel, wrasse (Halichoeres tenuispinnis), and black sea bream (Acanthopagrus schlegelii). In contrast, the eDNA analysis detected two species that were not observed in the visual census, namely, Japanese anchovy (Engraulis japonicus) and temperate seabass (Lateolabrax japonicus). These two species were, however, recorded in surveys undertaken in previous years. Although certain problems need to be resolved, the eDNA method represents a promising tool for fish surveys in marine ecosystems.
    Full-text · Conference Paper · Aug 2014
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    Michelle L. Walsh · Reiji Masuda · Yoh Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: Flatfish reared for stock enhancement often exhibit irregular behavioral patterns compared with wild conspecifics. These “deficits”, mostly attributed to the unnatural characteristics of the hatchery environment, are assumed to translate to increased predation risk. Initially releasing fish in predator-free conditioning cages may help flatfish adjust to the wild environment, establish burial skills, begin pigment change, recover from transport stress, and experience natural (live) food sources before full release into the wild. However, the impact of cage conditioning on the performance and behavior of flatfish has yet to be fully assessed. We conducted video trials with 10-cm, hatchery-reared Japanese flounder, Paralichthys olivaceus, in sand-bottomed aquaria to assess four treatments of flounder: (1) reared fish cage conditioned for 7 d in the shallow coast, (2) reared fish directly from hatchery tanks, (3) wild fish, and (4) reared fish released directly from hatchery tanks into the wild and then recaptured after 6 d at large. Burying ability, predation, and threat response to a model predator were examined. Wild fish buried most, followed by cage conditioned, and released-then-recaptured and non-conditioned (directly from tank) fish. Wild and conditioned fish revealed much lower variation in total movement duration, which corresponded with lower levels and variation in prey vertical movement. Fish of all condition types exhibited a lower number of attacks and off-bottom swimming events, and a lower movement duration when the model predator was in motion versus when it was still. This study is the first to evaluate the behavioral mechanisms of hatchery-reared flatfish that have been cage-conditioned or released-then-recaptured. In addition, we provide evidence that cage conditioning can enhance the performance of released flatfish.
    Full-text · Article · Jan 2014 · Journal of Sea Research
  • [Show abstract] [Hide abstract] ABSTRACT: In situ synchrotron radiation Fe-57 Mossbauer spectroscopy was used to study the C15 Laves phases RFe2 (R = Y,Gd) under ultra-high-pressure hydrogen in a diamond anvil cell. In both cases, the Fe-57 isomer shift showed a rapid increase at a few GPa, and once again showed a small increase at above P similar to 10 GPa. The quadrupole splitting also showed stepwise changes. As a marked effect, a two-step magnetic transition was clearly observed for RFe2 (R = Y,Gd). The results indicate that two different hydride phases appear in the RFe2 H reaction system under the hydrogen pressure (up to 34 GPa).
    No preview · Article · Dec 2013 · Journal of Alloys and Compounds
  • Author K Takahashi · Reiji Masuda · Yoh Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: We assessed whether the development of observational learning in jack mackerel Trachurus japonicus juveniles corresponds with that of their schooling behaviour. Schooling behaviour was quantitatively analysed by nearest neighbour distance and separation angle in two size classes of fish, 20-mm and 40-mm in body length. Observer and non-observer fish with matching sizes were conditioned to pellets by temporarily stopping aeration. Observer fish were provided with five observation trials of other individuals feeding near an air stone when aeration was stopped. After the observation trial, fish were conditioned to pellets with the stop of aeration, and then the learning process was evaluated by the increase in the association with the feeding area when aeration was stopped. In 20-mm fish, which were at an immature stage of schooling behaviour, there was no difference in the learning process between observer and non-observer fish. In contrast, 40-mm fish were confirmed to have a well-developed schooling behaviour, and the observer learnt the feeding area more efficiently than the non-observer. This study provides evidence that observational learning develops along with the development of the social interaction.
    No preview · Article · Nov 2013 · Behavioural processes
  • K Takahashi · R Masuda · Y Yamashita
    [Show abstract] [Hide abstract] ABSTRACT: Animals in social environments can enhance their learning efficiency by observing the behaviour of others. Our previous study showed that learning efficiency of schooling fish increased through the observation of the behaviour of trained demonstrator conspecifics. The present study aimed to verify the key factor of observational learning by investigating what information is important for social transmission of feeding information. A striped jack (Pseudocaranx dentex) observer was provided with one of the five observation treatments: (a) pellets observation, where pellets were dropped near the aeration in an adjacent tank; (b) responding conspecific observation, where a trained conspecific demonstrator responded to the aeration without food in the adjacent tank; (c) foraging conspecific observation, where a conspecific demonstrator foraged near the aeration in the adjacent tank; (d) nearby pellets observation, where pellets were dropped in a transparent column near the aeration in the observer tank; and (e) foraging heterospecific observation, where a filefish (Stephanolepis cirrhifer) demonstrator foraged near the aeration in the adjacent tank. The response to the aeration in these observers was compared with that of controls who did not observe any behaviour. Only individuals who observed foraging conspecifics showed a response to the aeration after observing. These results suggest that observer fish acquire feeding information not through recognition of prey items or through imitation of the demonstrator, but through the vicarious reinforcement of a conspecific for foraging.
    No preview · Article · Oct 2013 · Animal Cognition
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    [Show abstract] [Hide abstract] ABSTRACT: We evaluated the effects of turbidity on school formation in ayu (Plecoglossus altivelis) [24.5 ± 2.2 mm standard length (Ls)], Japanese anchovy (Engraulis japonicus) (29.1 ± 3.1 mm Ls) larvae, which often live in turbid coastal waters, and yellowtail (Seriola quinqueradiata) juveniles (37.1 ± 2.5 mm Ls), which live in clear offshore waters. Fish were introduced into experimental tanks at one of five turbidity levels obtained by dissolving 0, 5, 20, 50, or 300 mg l−1 of kaolin in seawater. Their behaviour was video recorded, and the nearest neighbour distance (DNN) and separation angle (AS) were compared among turbidity levels. Mean DNN of ayu was significantly smaller at 20 and 50 mg l−1 than any other level of turbidity, as was AS at 20 mg l−1 compared with 0 mg l−1. Mean AS of anchovy was smaller at 50 mg l−1 of turbidity than any others. In contrast, mean DNN of yellowtail was larger at 300 mg l−1 than any others. These results suggest that moderate turbidities enhance schooling behaviour in ayu and Japanese anchovy larvae, whereas turbidity has an inhibitive effect on schooling of yellowtail juveniles, corresponding well to the habitat characteristics of each species.
    Preview · Article · May 2013 · ICES Journal of Marine Science
  • [Show abstract] [Hide abstract] ABSTRACT: Staining-type hypermelanosis, defined as blind-side melanosis occurring after completion of metamorphosis, reduces commercial value in hatchery-produced flatfishes. Detailed characterization was performed on the stained area of juvenile Japanese flounder Paralichthys olivaceus to physiologically understand this phenomenon. From 80 to 120 days after hatching, juveniles were reared in sandy and sandless tanks. By classifying the staining degree into 7 levels, about 2 times higher occurrence of middle-level staining was reconfirmed in sandless tank (about 80 %) than in sandy tank (about 40 %). In the stained area, we found 3 types of chromatophores (melanophore, xanthophore, and iridophore) and ctenoid scales, which would be typically observed on the normal ocular side. Detailed examination on the melanophores revealed further similarity between the stained area and the normal ocular side, in terms of the distribution at 2 layers (shallower and deeper than scale), and the densities in both layers (about 1000 cells/mm2 above scale and 200 cells/mm2 beneath scale). These results strongly suggest that the staining is a status change in the body surface conditions from the blind side to that on the ocular side, and not a simple darkening caused by disordered proliferation of melanophores on the blind side.
    No preview · Article · Mar 2013 · Fisheries Science
  • Li J · Haga Y · Masuda R · Takahashi K · Ohta H · Ishida S · Satoh S
    [Show abstract] [Hide abstract] ABSTRACT: A feeding experiment was conducted to investigate the effects of feeding live food (LF) and two microdiets [MDs; commercial MD (CD) and peptide-based MD (PMD)] on the growth, survival, digestive enzyme activity, and RNA/DNA ratio in Japanese flounder Paralichthys olivaceus larvae. Flounder larvae at 21 days post hatching (dph) were fed two types of MDs with 1/6 LF or LF for 18 days. At 38 dph, significantly higher survival was observed in larvae fed LF than those fed CD +1/6 LF and PMD +1/6 LF. At 38 dph, significantly higher body weight was observed in larvae fed CD + 1/6 LF than LF and PMD + 1/6 LF. Significantly higher RNA/DNA ratios were observed in larvae fed LF than CD+1/6 LF or PMD + 1/6 LF during 23-32 dph. However, there was no difference in RNA/DNA ratios in larvae fed CD+1/6 LF and PMD+1/6 LF at all time examined. Significantly higher amylase, lipase and trypsin activities were observed in fish fed 1/6 LF at 29 and 32 dph. Protease activity of fish fed 1/6 LF was significantly higher at 35 dph. No marked difference was observed in enzyme activities in fish fed two MDs.
    No preview · Article · Jan 2013
  • [Show abstract] [Hide abstract] ABSTRACT: The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0 W/m 2 ) for 4 h. Survival rate was measured every 2 h for a period of 24 h (red sea bream) or 48 h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0 % 24 h after exposure at the 1.1 and 1.8 W/m 2 levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8 W/m 2 . Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species.
    No preview · Article · Jan 2013 · Environmental Biology of Fishes

Publication Stats

1k Citations
119.67 Total Impact Points


  • 2000-2015
    • Kyoto University
      • • Advanced Education and Research Center of Energy Science
      • • Division of Applied Biosciences
      Kioto, Kyōto, Japan
  • 1997-2008
    • The University of Tokyo
      • Institute of Atmosphere and Ocean Research
      Tōkyō, Japan
  • 1998-2005
    • Oceanic Institute
      Waimānalo, Hawaii, United States