Low-fidelity homing behaviour of Biwa salmon <Emphasis Type="Italic">Oncorhynchus</Emphasis> sp. landlocked in Lake Biwa as inferred from otolith elemental and Sr isotopic compositions

Biwa salmon Oncorhynchus sp. is endemic to Lake Biwa, Japan, where it is an important commercial and recreational fisheries species. However, no information is currently available on its population structure and migration ecology. Therefore, here we evaluated whether otolith Sr/Ca, Ba/Ca and ⁸⁷Sr/⁸⁶Sr ratios can be used as natural signatures in Biwa salmon and then used these to determine the natal origins of lake-migration-phase individuals and spawning adults, and the homing ability of spawning adults in the Lake Biwa water system. Quadratic discriminant function analysis demonstrated that the lake-migration school comprised individuals with multiple origins, including rivers to the east, west and north of Lake Biwa, and that the homing rate of spawning adults was low (18 out of 80 individuals), with ca. 78% of fish straying into non-natal rivers. However, this straying behaviour was not spatially random, with fish tending to migrate upstream in rivers neighbouring their natal rivers. The high rate of straying in spawning adults is considered important for establishing and maintaining this species, which is highly adapted to life in the Lake Biwa water system where environmental disturbances often occur.     

Interspecific differences in the post-settlement survival of <Emphasis Type="Italic">Acropora</Emphasis> corals under a common garden experiment

Extremely low post-settlement survival is one of the largest barriers for artificial rehabilitation of Acropora corals. However, little data have been found for interspecific difference of the post-settlement survival probably because the observation of coral juvenile is difficult in the field. Here, we analyzed the survival of three dominant species of Acropora corals (A. digitifera, A. tenuis, A. yongei), with different colony morphologies and habitat preferences, for 2 years after settlement under the same environmental conditions. The post-settlement survival was significantly higher for A. tenuis than for A. digitifera 3 months after settlement. Two years later, the survival rate of A. tenuis was approximately 15 times higher than A. digitifera. In a separate analysis of three bottle-brush species (A. awi, A. echinata, A. subglabra) and A. tenuis, post-settlement survival was always higher for A. awi than for other two bottle-brush species, suggesting that the initial survival was different among morphologically sister species. Low survival was possibly associated with slow growth rates during the first 7 months. Thus, species selection is important for successful artificial coral rehabilitation, with A. tenuis being the most viable option. Alternatively, new techniques are required to improve post-settlement survival of slow growing coral species.     

Identification of a peptide in enzymatic hydrolyzate of cheese that inhibits ovalbumin permeation in Caco-2 cells

Because the first step in the triggering of food allergy is the permeation of the allergen through the intestine, enhancement of the intestinal barrier function is thought to be effective for preventing food allergy. In this study, a peptide that inhibits ovalbumin (OVA) permeation in an in vitro Caco-2 cell model was isolated from enzymatic hydrolyzate of cheese (EHC). Amino acid sequence analysis identified the active peptide as GPIVLNPWDQ, a sequence identical to amino acids 102-111 of alphas2-casein. The decapeptide significantly inhibited OVA permeation at a concentration of 10(-6) M. In addition, it was found that a pentapeptide half, NPWDQ, is essential for the inhibitory activity because NPWDQ but not GPIVL had nearly the same inhibitory activity as GPIVLNPWDQ. The possibility exists that EHC and/or peptides possessing the NPWDQ sequence can be practically applied to the prevention of food allergy.     

Vertical behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean based on archival tag data

The behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean was investigated using archival tag data for 28 fish [49–72 cm fork length (FL) at release, 3–503 days] released in Japanese waters around the Nansei Islands (24–29°N, 122–132°E) and east of central Honshu (Offshore central Honshu, 32–36°N, 142–148°E). Vertical behavior was classified into three types based on past studies: ‘characteristic’ (non‐associative), ‘associative’ (associated with floating objects) and ‘other’ (behavior not fitting into these two categories). The proportion of fish showing associative behavior decreased and that of characteristic behavior increased as fish grew, and this shift was pronounced at 60–70 cm FL. The fish usually stayed above the 20°C isotherm during the daytime and nighttime when showing associative behavior and below the 20°C isotherm during daytime for characteristic behavior. A higher proportion of characteristic behavior was seen between December and April around the Nansei Islands, and between September and December for offshore central Honshu. Seasonal changes in vertical position were also observed in conjunction with changes in water temperature. In this study, ‘other’ behavior was further classified into five types, of which ‘afternoon dive’ behavior, characterized by deep dives between around noon and evening, was the most frequent. The present study indicated that in the northwestern Pacific Ocean, the vertical behavior of bigeye tuna changes with size, as well as between seasons and regions.     

Density estimation of the giant jellyfish Nemopilema nomurai around Japan using an alternative modified detection function for left truncation in a line transect survey

Information on the distribution and bloom scale of the giant jellyfish Nemopilema nomurai is necessary to understand the impact on fisheries. In October 2009, we had an opportunity for visual counting of N. nomurai around Japan from a research/training vessel. To take into account possibly severe missed detection of N. nomurai in the close vicinity of the vessel, detection functions were modified by introducing an additional parameter δ expressing the proportion of detectable N. nomurai within a threshold perpendicular distance. Some covariate effects in the detection process were also investigated. The δ-modified hazard-rate detection function with δ variation parameter of jellyfish body size was chosen as the best-fit one by AIC model selection. The results suggested that a higher proportion (>30 % or more) of N. nomurai were undetected in the vicinity of vessel. The δ-modified model had an advantage of no loss of left-truncated data and provided better estimation of density with the smaller coefficient of variation than the conventional left truncation approach. It is applicable to other line transect surveys, e.g. aerial surveys. High densities of N. nomurai were found in the central part of the Sea of Japan and off Iwate Prefecture.     

Effect of environmental factors and prey species on daytime and nighttime vertical distribution of juvenile walleye pollock in and around Funka Bay

We examined factors affecting the vertical distribution of juvenile walleye pollock during “the second critical period” (i.e. the transition period of prey size) in and around Funka Bay, Hokkaido, Japan. During the day, small juveniles (<30 mm) were distributed mainly in shallow, warm, and low-salinity water within the bay, whereas larger ones (≥30 mm) occurred in deeper, cold and saline water. During the night, the large juveniles migrated to shallower depths. Outside the bay, small- and large-sized juveniles were distributed in water masses of similar physical properties during the daytime, whereas during the nighttime, most of the juveniles moved to shallower depth, and some juveniles dived to deeper water mass. Dietary analysis revealed that large juveniles fed on large copepods (≥0.5 mm in body width) more than small juveniles did. The composition of zooplankton in our survey area showed that large-sized copepods often occurred in deeper saline water. From these results, there is a possibility that juvenile pollock inside and outside Funka Bay occupied different water masses preferable for each feeding advantage.     

Involvement of circadian clock in crowing of red jungle fowls (Gallus gallus)

The rhythmic locomotor behavior of flies and mice provides a phenotype for the identification of clock genes, and the underlying molecular mechanism is well studied. However, interestingly, when examining locomotor rhythm in the wild, several key laboratory‐based assumptions on circadian behavior are not supported in natural conditions. The rooster crowing ‘cock‐a‐doodle‐doo’ is a symbol of the break of dawn in many countries. Previously, we used domestic inbred roosters and showed that the timing of roosters' crowing is regulated by the circadian clock under laboratory conditions. However, it is still unknown whether the regulation of crowing by circadian clock is observed under natural conditions. Therefore, here we used red jungle fowls and first confirmed that similar crowing rhythms with domesticated chickens are observed in red jungle fowls under the laboratory conditions. Red jungle fowls show predawn crowing before light onset under 12:12 light : dim light conditions and the free‐running rhythm of crowing under total dim light conditions. We next examined the crowing rhythms under semi‐wild conditions. Although the crowing of red jungle fowls changed seasonally under semi‐wild conditions, predawn crowing was observed before sunrise in all seasons. This evidence suggests that seasonally changed crowing of red jungle fowls is under the control of a circadian clock.     

The T allele at the g.1471620G>T in the EDG1 gene associated with high marbling in Japanese Black cattle is at a low frequency in breeds not selected for marbling

Our previous study detected a single nucleotide polymorphism (SNP), g.1471620G > T , in the 5' flanking region of the endothelial differentiation sphingolipid G-protein-coupled receptor 1 ( EDG1 ) gene, which has been considered as a positional functional candidate for the gene responsible for marbling, and showed association of the g.1471620G > T SNP with marbling in Japanese Black beef cattle. In the present study, we investigated the allele frequency distribution of the g.1471620G > T SNP among the 5 cattle breeds, Japanese Black, Japanese Brown, Japanese Short Horn, Holstein, and Brown Swiss breeds. The T allele at the g.1471620G > T SNP associated with high marbling was found at high frequency in Japanese Black breed that has been subjected to a strong selection for high marbling, while the allele was absent or at very low frequencies in the other breeds that have not been strongly selected for high marbling. Based on this finding, we hypothesized that the pressure of the strong selection for high marbling in Japanese Black breed has increased the frequency of the T allele at the g.1471620G > T SNP in the EDG1 .     

Immunohistochemical detection of phosphatidylserine and thrombospondin on denucleating erythroblasts in rat bone marrow

The hypothesis that apoptotic factors play some roles in the denucleation of erythroblasts has been confirmed by the immunohistological detection of both phosphatidylserine and thrombospondin as phagocytosis-inducing factors in general apoptotic events. Both phosphatidylserine and thrombospondin were detected on the surface of cell membrane of mature erythroblasts, while thrombospondin was also detected in more immature erythroblasts. The intensities of their immune reactions increased as the erythroids matured. During denucleation, the positivities of both phosphatidylserine and thrombospondin were restricted on the surface of the cell membrane surrounding the protruding nuclei. Thus, the apoptotic process involves denucleation of erythroblasts and phosphatidylserine, and thrombospondin acts as phagocytosis-inducing factors in the denucleation event.