http://hdl.handle.net/2261/5675 Tue, 21 May 2013 03:11:23 GMT 2013-05-21T03:11:23Z http://hdl.handle.net/2261/51714 タイトル: Observations of gut contents of leptocephali in the North Equatorial Current and Tomini Bay, Indonesia 著者: Miller, Michael J.; Otake, Tsuguo; Aoyama, Jun; Wouthuyzen, Sam; Suharti, Sasanti; Sugeha, Hagi Y.; Tsukamoto, Katsumi 抄録: Visible objects in the gut contents of 13 leptocephali of 11 species and 8 families of eels were observed using photographs of daytime-caught larvae in two different types of marine habitats: the open ocean (North Equatorial Current) and a semi-enclosed deep-water bay (Tomini Bay of Sulawesi Island, Indonesia). Zooplankton fecal pellets of at least 3 shapes, transparent oval objects, and one apparent appendicularian were observed to have been ingested. These types of objects are consistent with the hypothesis that leptocephali consume marine snow and discarded appendicularian houses, which both typically contain fecal pellets. Appendicularians have not been previously reported to be consumed by leptocephali, but the apparent presence of one in a muraenid intestine suggests that they may occasionally be consumed along with their houses. Chlopsid leptocephali in both regions were observed to have consumed large amounts of food material, which indicated that their short intestines are able to expand more than previously known. Due to net avoidance, most leptocephali are collected at night when feeding may be reduced, so visible food materials are rarely observed in their intestines at night. These photographs show some marine snow-related objects that are consumed by leptocephali more clearly than previous reports. Tue, 20 Mar 2012 00:00:00 GMT http://hdl.handle.net/2261/51714 2012-03-20T00:00:00Z http://hdl.handle.net/2261/51713 タイトル: Lack of genetic heterogeneity in the Japanese eel based on a spatiotemporal sampling 著者: Minegishi, Yuki; Aoyama, Jun; Yoshizawa, Natsuko; Tsukamoto, Katsumi 抄録: To determine the population structure of the Japanese eel Anguilla japonica, both geographic and temporal genetic variations in a total of 724 of newly recruited glass eels were investigated using six microsatellite loci. F-statistics found no significant genetic difference among nine localities covering the species range (FST=-0.0091-0.0207, RST=-0.0086-0.0207, P>0.05). No inter- or intra-annual changes in genetic variation were observed in pairwise comparisons of F-statistics (FST=-0.0054-0.0108, RST=-0.0143-0.0401, P>0.05) and AMOVA (FCT=0.0009, P>0.05), respectively. The results of the present study showed that the Japanese eel consists of a genetically homogeneous population in time and space. This information will be helpful for planning efficient stock management and conservation of this species. Tue, 20 Mar 2012 00:00:00 GMT http://hdl.handle.net/2261/51713 2012-03-20T00:00:00Z http://hdl.handle.net/2261/51712 タイトル: Effects of larval ontogeny, turbulence, and prey density on survival in red sea bream Pagrus major larvae 著者: Kato, Yoshiki; Ohshima, Masakane; Yamashita, Yoh; Kitagawa, Takashi; Kimura, Shingo 抄録: The effect of turbulence on red sea bream larvae survival was tested at two prey densities and four turbulence levels in the laboratory for red sea bream. The effect of ontogenic stage on feeding behavior parameters was examined. The range of turbulence at which red sea bream larvae could survive and ingest prey increased with larval growth. Therefore, turbulence is an important condition impacting survival of small larvae during the initial period of feeding. At low prey density, larvae fed at the highest feeding rate and had a high RNA : DNA ratio at a medium turbulence level on the order of 10(-6.5)m2s(-3). Thus, an optimum turbulence level induces faster growth, and it can be concluded that turbulence plays an important role in larval growth and survival. For interspecific comparison, a feeding success index calculated by numerical modeling in sea bream was compared to that of Pacific bluefin tuna using data reported by Kato et al. (2008). There were large differences in the index. The equivalent curve for red sea bream showed a linear relationship, while that for Pacific bluefin tuna showed a dome-shaped relationship. These results suggest that open-ocean-dwelling Pacific bluefin tuna likely prefer prey that is moving and under conditions of moderate turbulence. Further, tuna requires a greater degree of turbulence during initial feeding periods than does red sea bream. Tue, 20 Mar 2012 00:00:00 GMT http://hdl.handle.net/2261/51712 2012-03-20T00:00:00Z http://hdl.handle.net/2261/51711 タイトル: Autofluorescent bodies in the toxic dinoflagellate Alexandrium tamarense: A potential indicator of the physiological condition of the species 著者: Kaga, Shinnosuke; Koike, Kazuhiko; Sekiguchi, Katsushi; Shinohara, Natsumi; Kobiyama, Atsushi; Yamada, Yuichiro; Ogata, Takehiko 抄録: Autofluorescent bodies were examined in cultured and natural cells of Alexandrium tamarense (Lebour) Balech collected from Ofunato Bay, Japan. Three different autofluorescent bodies (pale blue, light blue, and white) and the autofluoresced chloroplast were observed under ultraviolet light excitation. We suggest that the pale-blue and light-blue bodies represent a novel type in dinoflagellates based on their fluorescent properties. We also found that cells with pale-blue and light-blue bodies appeared predominantly in the early and middle to late exponential phases, respectively. A similar pattern was observed in natural populations during a 2-year field survey. Cells with pale-blue bodies were dominant almost one week before the bloom, whereas those with light-blue bodies were mostly apparent during the blooming stage. These results indicate that the observation of autofluorescent bodies could be useful as a physiological indicator for predicting natural population blooms of A. tamarense in Ofunato Bay. Tue, 20 Mar 2012 00:00:00 GMT http://hdl.handle.net/2261/51711 2012-03-20T00:00:00Z