Environmental influences on late-summer individual Japanese eel diel activity and space utilization patterns in a shallow western Japan brackish lake

The late-summer diel activity patterns and space utilization of five Japanese eels, Anguilla japonica, were investigated using an acoustic telemetry positioning system in a shallow brackish lake in western Japan. Eels were highly nocturnal and crepuscular, with 98.1% of positions detected between sunset and sunrise, and were more active during dusk and dawn compared with nighttime, and during full moons compared with other lunar periods. Most diurnal activity occurred during darker conditions, and two individuals extended their activity into the morning, suggesting that overcast skies reduced light intensity and prolonged nocturnal activity into daytime. Individual eels had different home-range patterns, but appeared to rest nearshore during the day, with space utilization expanding offshore at dusk and night, followed by returning to nearshore at dawn. Their home ranges and core activity areas were bordered by the shoreline, with eels tending to exhibit small activity spaces and strong site fidelity. This study provides valuable ecological knowledge about the individual behavior of eels inhabiting a small brackish lake at the northern limit of the natural distributional range of the species along the Sea of Japan, which can contribute to management and conservation of the species.

     

Detection of novel kobu-like viruses in Japanese black cattle in Japan

During surveillance for bovine diarrhea of unknown causes in Japanese black cattle in Kagoshima Prefecture,Japan, we found two types of novel kobu-like viruses in fecal samples of calves. Sequence analyses revealedthat they had L protein and 2A protein with H-box/NC sequence motif, which are present in kobuviruses.Phylogenetic analysis revealed that they were related to kobuviruses; however, they clustered apart from otherkobuviruses. In the prevalence study of two types of novel kobu-like viruses, 16.9% and 10.4% prevalence ofthese viruses were observed in the feces of diarrheal calves in this area.     

Effects of nutrient enrichment,irradiance control,and boiling on the color of the brown alga <Emphasis Type="Italic">Undaria pinnatifida</Emphasis>

The color of Undaria pinnatifida after boiling is an important factor determining its marketable value. Our previous study showed that decreased nutrients and elevated irradiance resulted in increases of lightness and yellowness (i.e., discoloration) of this alga. However, little is known about the optimal levels of nutrients and irradiance required to decrease these color values and the combined effects of these factors and boiling. We conducted two culture experiments to test the effects of nutrients (non-enriched and 1.25, 5, and 25% PESI enriched treatments), irradiance (0, 10, 30, and 180 µmol m^?2 s^?1), and boiling on lightness L*, redness a*, and yellowness b* of this alga. L* and b* did not differ between non-enriched and 1.25–5% PESI treatments, but were lower in the 25% PESI treatment. L* and b* were lowest at 0–10 µmol m^?2 s^?1, although negative growth occurred at 0 µmol m^?2 s^?1. Decreased irradiance had a positive or little effect on a* before boiling, but had a negative effect after boiling. These results suggest that around 25% PESI and 10 µmol m^?2 s^?1 were the optimal levels to decrease the three color values of this species after boiling.     

Environmental DNA analysis reveals the spatial distribution,abundance, and biomass of Japanese eels at the river‐basin scale

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Variations in the abundance of Pacific saury (Cololabis saira) from the northwestern Pacific in relation to oceanic-climate changes

Effects of oceanic-climate changes on the abundance of Pacific saury (Cololabis saira) in the northwestern Pacific during the last half century were investigated. Abundance indices of both large and medium size groups exhibit interannual–decadal variations, but their patterns were different. The large and medium size groups of saury are corresponding to the recruitments of winter- and spring-cohort, respectively. The abundance of large size group saury was significantly correlated with the winter sea surface temperature (SST) in the Kuroshio region, whereas the medium size group saury showed high correlations with SST in the Kuroshio–Oyashio transition zone and the Oyashio region, indicating that the two size groups are affected by subtropical and subarctic environment, respectively. Significant negative correlation between the abundance index and the southern oscillation index (SOI) suggested that El Niño-southern oscillation (ENSO) events have marked impacts on the large size group saury. Subtropical high pressure index and far east zonal index also show high correlations with the abundance of both large and medium size group saury, indicating a linkage between large-scale atmospheric circulation and the abundance of saury. These correlations demonstrate that the abundance of Pacific saury is directly affected by the SST fields through large-scale atmosphere–ocean interactions from the equatorial Pacific to mid- and high-latitude areas such as El Niño events.     

Predation on glass eels of Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> in the Tone River Estuary,Japan

Aquaculture of Japanese eel Anguilla japonica relies upon the natural recruitment of their glass eels (juveniles); however, predation that could influence glass eel recruitment remains unknown. In the present study, we aimed to elucidate the proportion of predation on A. japonica glass eels through stomach content analysis of predatory fishes collected in the estuary region of the Tone River system and its vicinity in Japan. Species of the predated glass eels were identified by DNA barcoding. A total of 270 predatory fishes of 15 taxa was collected over 2 years. The overall proportion of predation on glass eels, genetically identified as Japanese eel, was 0.7%, but this rose to 2.0% when data were limited to fishes caught during the peak months of glass eel recruitment. A glass eel was found in the stomach contents of a channel catfish Ictalurus punctatus, an invasive species in this river system, and a blackfin sea bass Lateolabrax latus. These fishes are therefore considered potential predators of A. japonica glass eels. However, as the proportion of predation was low, and the glass eels represented only small proportions of predator stomach contents, further investigation is needed for a better understanding of predation on A. japonica glass eels, and its effects on the early life stages of this endangered species.     

Growth effect on the otolith and somatic size relationship in Japanese anchovy and sardine larvae

ABSTRACT:   Relationships between otolith and somatic sizes were examined for Japanese anchovy Engraulis japonicus and sardine Sardinops melanostictus larvae collected broadly in the western North Pacific, based on a substantial data set derived from a previous paper. Allometric formulae showed close fits to the relationships between otolith radius and standard length, and the formulae differed between anchovy and sardine larvae. Despite the high correlations, the effect of somatic growth rate on the otolith and somatic size relationship (the 'growth effect') was significantly detected for both anchovy and sardine larvae. Slower growing larvae tended to have larger otoliths than faster growing conspecifics at the same somatic size. This growth effect was more obvious for sardine larvae than for anchovy larvae, probably because of their differential responses of somatic growth to temperature shifts. The growth effect could lead to the possibility of biases in the back-calculation and size estimation processes. As the growth effect is considered to be a general phenomenon and its extent to be species-specific, the relationship between otolith and somatic size and its uncoupling should be scrutinized before application of techniques based on the otolith and somatic size correlation.     

Daily growth increment formation and its lunar periodicity in otoliths of the myctophid fish Myctophum asperum (Pisces: Myctophidae)

ABSTRACT: The surface-migratory myctophid fish, Myctophum asperum , of the western North Pacific was found to have daily growth increments of its sagittal otolith, which also exhibited lunar periodicity in the deposition of increments. Daily deposition of the otolith increments was verified because the width of the marginal increment increased during the night and early morning between 20.00 h and 08.00 h and its growth stopped during the day. An autocorrelation analysis of the increment widths, which were measured consecutively in 11 specimens covering 33 synodic months, also showed a lunar periodicity in increment deposition. The mean increment widths during five days around the time of a full moon were significantly narrower than those around a new moon in 18 of the 33 full moon cases ( P < 0.01: Student's t -test) and, on average, tended to be narrow in 29 cases. The cause of this tendency is thought to be slower growth caused by staying in deeper and colder habitat due to the suppression of diel vertical migration and/or lower food availability resulting from the possible dispersion of zooplankton during the full moon period.