Reiji Masuda

Kyoto University, Kioto, Kyōto, Japan

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Publications (83)96.27 Total impact

  • Mai Yamaguchi · Reiji Masuda · Yoh Yamashita ·

    Fisheries Science 11/2015; DOI:10.1007/s12562-015-0944-x · 0.88 Impact Factor
  • Hirona Makino · Reiji Masuda · Masaru Tanaka ·

    Fisheries Science 09/2015; DOI:10.1007/s12562-015-0917-0 · 0.88 Impact Factor
  • Kohji Takahashi · Reiji Masuda · Yoh Yamashita ·
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    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.
    Fisheries Science 05/2015; 81(4). DOI:10.1007/s12562-015-0881-8 · 0.88 Impact Factor
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    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.
    NIPPON SUISAN GAKKAISHI 01/2015; 81(4):701-714. DOI:10.2331/suisan.81.701 · 0.15 Impact Factor
  • Koji Tokuda · Reiji Masuda · Yoh Yamashita ·
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    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.
    Journal of Ethology 01/2015; 33(1). DOI:10.1007/s10164-014-0414-4 · 0.97 Impact Factor
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    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.
    NIPPON SUISAN GAKKAISHI 11/2014; 80(6):934-945. · 0.15 Impact Factor
  • Reiji Masuda ·
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    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.
    American Fisheries Society 144th Annual Meeting; 08/2014
  • Yuichi Fukunishi · Reiji Masuda ·
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    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.
    American Fisheries Society 144th Annual Meeting; 08/2014
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    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.
    99th ESA Annual Convention 2014; 08/2014
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    Michelle L. Walsh · Reiji Masuda · Yoh Yamashita ·
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    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.
    Journal of Sea Research 01/2014; 85:447–455. DOI:10.1016/j.seares.2013.07.019 · 1.99 Impact Factor
  • Author K Takahashi · Reiji Masuda · Yoh Yamashita ·
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    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.
    Behavioural processes 11/2013; 103. DOI:10.1016/j.beproc.2013.10.012 · 1.57 Impact Factor
  • K Takahashi · R Masuda · Y Yamashita ·
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    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.
    Animal Cognition 10/2013; 17(2). DOI:10.1007/s10071-013-0686-z · 2.58 Impact Factor
  • Ryosuke Ohata · Reiji Masuda · Kohji Takahashi · Yoh Yamashita ·
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    ABSTRACT: We evaluated the effects of turbidity on school formation in ayu (Plecoglossus altivelis) [24.5 +/- 2.2 mm standard length (L-s)], Japanese anchovy (Engraulis japonicus) (29.1 +/- 3.1 mm L-s) larvae, which often live in turbid coastal waters, and yellowtail (Seriola quinqueradiata) juveniles (37.1 +/- 2.5 mm L-s), 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 (D-NN) and separation angle (A(S)) were compared among turbidity levels. Mean D-NN of ayu was significantly smaller at 20 and 50 mg l(-1) than any other level of turbidity, as was A(S) at 20 mg l(-1) compared with 0 mg l(-1). Mean A(S) of anchovy was smaller at 50 mg l(-1) of turbidity than any others. In contrast, mean D-NN 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.
    ICES Journal of Marine Science 05/2013; 71(4):925-929. DOI:10.1093/icesjms/fss194 · 2.38 Impact Factor
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    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.
    Fisheries Science 03/2013; 79(2). DOI:10.1007/s12562-013-0600-2 · 0.88 Impact Factor
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    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.
    Environmental Biology of Fishes 01/2013; 96(1):13-20. DOI:10.1007/s10641-012-0017-2 · 1.57 Impact Factor
  • Reiji Masuda · Katsuhiro Matsuda · Masaru Tanaka ·
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    ABSTRACT: The diel activity rhythm of red-spotted grouper Epinephelus akaara was studied both in captivity and in the wild. Behavior of solitary grouper (58 to 397 mm in total length) in a tank was video recorded using infrared illuminators under 11L/10D and two 1.5-h twilight transition periods, and was compared to that of banded wrasse Halichoeres poecilopterus, a typical diurnal fish. Underwater observations using SCUBA were also conducted in their natural habitat to reveal the behavioral activity together with a visual census of adjacent fish and crustacean assemblages. Red-spotted grouper showed a strong nocturnal activity in a tank regardless of body size as opposed to the strongly diurnal banded wrasse. Activity of groupers in natural waters was high at dawn and dusk, low at noon, and only a few individuals were observed at night. Visual census in the habitat revealed that fish abundance and species richness was highest at noon, lowest at night, and intermediate at dawn and dusk. The opposite trend was found in crustacean assemblages. Absence of groupers at night may reflect their nocturnal feeding migration away from the study area. Alternatively, the crepuscular activity of groupers in the wild is suggested to be an adaptation to feed on small fishes that shift between daytime activity and nighttime rest and/or on nocturnal crustaceans that show the opposite activity pattern.
    Environmental Biology of Fishes 11/2012; 95(3). DOI:10.1007/s10641-012-0006-5 · 1.57 Impact Factor
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    ABSTRACT: Marine fishes often experience major habitat shifts during their life history, and previous studies have shown that the learning capability of fish change ontogenetically and in accordance with such habitat shifts. However, because all of these studies used a single type of conditioned stimuli (CS), they failed to detect qualitative changes in learning capability. Here we tested the hypothesis that preparedness for learning changes ontogenetically in jack mackerel Trachurus japonicus, which undergo a drastic change in habitat preference during their life history as they move from offshore pelagic waters to coastal and demersal rocky reefs. Groups of juveniles measuring 40 mm standard length (SL) (pelagic stage) and 60 mm SL (demersal stage) were conditioned to food rewards in response to three different CS; the presence of a surface structure, mid-water structure, and aeration. The results showed that small juveniles tended to become conditioned to the surface stimulus faster than they did to the mid-water stimulus. Conversely, large juveniles responded to the mid-water stimulus significantly more quickly than they did to the surface stimulus. These results suggest that stimulus-specific learning capability in T. japonicus changes ontogenetically, facilitating adaptation to their life-history strategy.
    Journal of Ethology 05/2012; 30(2). DOI:10.1007/s10164-012-0328-y · 0.97 Impact Factor
  • Kohji Takahashi · Reiji Masuda · Yoh Yamashita ·
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    ABSTRACT: We aimed to evaluate the effect of social interaction on learning in juvenile jack mackerel Trachurus japonicus. We first compared the learning process between single fish and groups of fish. Reward-conditioned learning was established in eight trials in both treatments, whereas individuals in the group treatment responded to stimuli more frequently in the feeding area than in the single fish. This implies that information about the feeding area was shared in the group and pursuing other individuals gave them a behavioral advantage for feeding. We then investigated whether information on the feeding area can be transmitted through observation of other individuals in aligned tanks. Fish in the control group required six trials to be conditioned to aeration stimuli and feeding location, whereas those in the observation treatment required only three trials for this learning. This result implies that information on the feeding area was transmitted through visual observations. The present research suggests that sharing and transmission of information occur in schools of jack mackerel. Schooling behavior would thus enable optimization of the foraging behavior in this species.
    Fisheries Science 03/2012; 78(2). DOI:10.1007/s12562-011-0454-4 · 0.88 Impact Factor
  • Kohji Takahashi · Reiji Masuda · Yoh Yamashita ·
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    ABSTRACT: We examined the effect of bottom feeding and net chasing as means to improve the maladaptive off-bottom swimming of hatchery-reared Japanese flounder Paralichthys olivaceus juveniles for stock enhancement. Three treatments were tested: (1) a bottom feeding treatment in which fish were fed near the bottom; (2) a net chasing treatment in which fish were chased by a hand net two to four times a day, and (3) a surface feeding treatment in which fish were fed from the surface (control treatment). Foraging behavior at the surface with surface feeding was analyzed 1 day before initiating these treatments and 2 weeks thereafter. A comparison of the pre- and post-treatments revealed that off-bottom swimming was less in the bottom feeding treatment and net chasing treatments. A comparison of off-bottom swimming in the bottom feeding treatment between the pre- and post treatments revealed that bottom fed fish showed less off-bottom swimming than surface fed fish. These findings suggest that fish behavior can be manipulated during the rearing period and that such manipulations can be used to improve the behavior of fish for release.
    Fisheries Science 01/2012; 79(1). DOI:10.1007/s12562-012-0572-7 · 0.88 Impact Factor
  • R Ohata · R Masuda · Y Yamashita ·
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    ABSTRACT: Laboratory experiments revealed distinct effects of turbidity on the survival of Japanese anchovy Engraulis japonicus larvae when exposed to either visual (jack mackerel Trachurus japonicus) or tactile (moon jellyfish Aurelia aurita) predators. The experiments were conducted in 30 l tanks with three levels of turbidity obtained by dissolving 0, 50 or 300 mg l(-1) of kaolin. Predators were introduced to experimental tanks followed by larvae of E. japonicus ranging from 5 to 25 mm standard lengths (L(s) ). When exposed to T. japonicus, the mean survival rate of larvae was significantly higher in 300 mg l(-1) treatments compared to the other turbidity levels. When exposed to A. aurita, however, there was no difference in the survival rates among different turbidity treatments. The survival rates when exposed to either predator improved with larval growth. The logistic survivorship models for E. japonicus larvae when exposed to A. aurita had an inflection point at c. 12 mm L(s) , suggesting that their size refuge from A. aurita is close to this value. Comparison to a previous study suggests a high vulnerability of shirasu (long and transparent) fish larvae to jellyfish predation under turbidity. This study indicates that anthropogenic increases of turbidity in coastal waters may increase the relative effect of jellyfish predation on fish larvae.
    Journal of Fish Biology 12/2011; 79(7):2007-18. DOI:10.1111/j.1095-8649.2011.03141.x · 1.66 Impact Factor

Publication Stats

1k Citations
96.27 Total Impact Points


  • 2002-2015
    • Kyoto University
      • • Advanced Education and Research Center of Energy Science
      • • Division of Applied Biosciences
      Kioto, Kyōto, Japan
  • 1996-2008
    • The University of Tokyo
      • Institute of Atmosphere and Ocean Research
      Tōkyō, Japan
  • 1998-2005
    • Oceanic Institute
      Waimānalo, Hawaii, United States