The relationship between oocyte morphology and ovarian status in cattle

We investigated the relationships between oocyte morphology, follicular size and follicular waves using bovine ovaries derived from local abattoirs. Ovaries at the recruitment and selection phases contained larger numbers of oocytes with good developmental ability, although ovaries at the recruitment phase contained the largest numbers of follicles compared with ovaries at the selection and dominant phases. Dominant phase ovaries contained a high percentage of oocytes with as good developmental ability as selection phase ovaries; however, they contained the lowest total number of oocytes with good developmental ability. Small follicles under 3.0 mm in diameter contained large numbers of small and degenerating oocytes. In contrast, follicles more than 3.0 mm in diameter contained a higher percentage of oocytes with good developmental ability.     

Body-length frequency and spatial segregation of the North Pacific spiny dogfish <Emphasis Type="Italic">Squalus suckleyi</Emphasis> in Tsugaru Strait,northern Japan

The present study elucidated the length structure and habitat segregation of North Pacific spiny dogfish (SPD) Squalus suckleyi in the Tsugaru Strait of northern Japan. Length–frequency distributions using kernel density estimation were determined for SPD captured by the bottom longline fishery landed at Minmaya from 1999 to 2011 and at Ohma from 2007 to 2011. Length–frequency distributions significantly differed between landings at the two ports; SPD at Minmaya were on average larger (65–85 cm precaudal length: PCL) than at Ohma (55–75 cm PCL). This difference is evidence of the length-based spatial segregation of the SPD. The seasonal landing pattern of the SPD was also different between the two ports. The SPD landed at Minmaya were largest during February–June and SPD < 75 cm PCL were caught at Ohma throughout the year. This different landing pattern was related to seasonal differences in bottom-layer water temperatures between the two fishing grounds. Females were thought to be dominant at Minmaya, whereas males dominated in most of the catches at Ohma. These results suggest spatial patterns of sexual segregation for this species in the Tsugaru Strait and require elucidation of the SPD stock condition at Minmaya and Ohma.     

Laboratory observations of habitat selection in aestivating and active adult sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

In order to verify which factors affect habitat selection for aestivating and in the active adult Apostichopus japonicus, animals were tested for their selection of attachment site in an experimental device (1-m pipes) in which the perceived environmental stimuli (light intensity, degree of contact with a hard surface, geotaxis) varied depending on the attachment site. During the aestivating season, the animals showed a strong selection for attachment sites during the daytime and nighttime; they also showed positive stereotaxis (thigmotaxis), negative phototaxis, and negative geotaxis. The results suggest that (1) habitats are not suitable for the aestivating adult A. japonicus unless these three environmental requirements are satisfied.     

A progestin-based treatment with a high dose of estradiol benzoate normalizes cyclic changes in endometrial EGF concentrations and restores fertility in repeat breeder cows

The objective of the present study was to examine the efficacy of a progestin-based treatment with a high dose of estradiol benzoate (EB) to normalize the epidermal growth factor (EGF) profile in the uterine endometrium and restore fertility in repeat breeder cows. Repeat breeder cows without peaks in their endometrial EGF concentrations on Days 3 and 14 of the estrous cycle were used throughout the study. The effect of 1 (standard dose), 2.5 and 5 mg of EB in a progestin-based treatment protocol (EB1, EB2.5 and EB5 treatments, respectively; n=5 for each group) on endometrial EGF concentrations was first examined. The EB1 and EB2.5 treatments in the repeat breeder cows produced a suppressed response in endometrial EGF compared with EB1 treatment in the fertile controls (n=5) and failed to restore the normal EGF profile during the next estrous cycle. However, EB5 treatment produced an increase in EGF concentrations similar to the fertile controls and normalized the endometrial EGF profile. The effects of the EB1 and EB5 treatments (n=30 for each group) on the endometrial EGF profile and fertility were then examined in the repeat breeder cows. The proportion of cows, with an EGF profile normalized by the treatments was higher in the EB5 group (66.7%) than in the EB1 (30.0%) and untreated control (13.3%; n=30) groups (P<0.01). The pregnancy rates of the cows having a normal EGF profile after treatment in the EB1 and EB5 groups were similar (88.9 and 85.0%, respectively) and higher than those of the cows having an abnormal profile within the same groups (19.0 and 30.0%, respectively, P<0.01). In summary, the endometrial response to EB in terms of the EGF concentration was suppressed in repeat breeder cows. A high dose (5 mg) of EB in a progestin-based treatment was found to be effective for restoration of a normal EGF profile and fertility in repeat breeder cows having lesser endometrial EGF concentrations on Days 3 and 14.     

Influence of artificial headlands on fish assemblage structure in the surf zone of a sandy beach,Kashimanada Coast,Ibaraki Prefecture,central Japan

To determine the effects of artificial headlands (groins with an anchor-shaped head portion) on the surf-zone fish assemblage structure of a sandy beach with strong wave action, three study sites (headland site sheltered behind the head portion, pocket-beach site between two adjacent headlands and exposed reference site without headlands) were sampled on the Kashimanada Coast, central Japan, in summer and autumn in 2012 and 2013. Distinct differences in physical conditions were recognized between the headland site and the other two sites throughout the study period, the former being characterized by lower wave height and turbidity, finer sediment particles and richer detritus. The fish assemblage structures also differed among the sites, the headland site supporting greater species and individual numbers. Cluster analysis showed clear differences in species composition of fish assemblages between the headland site and the other two sites. In addition, small-sized fishes tended to be more abundant at the headland site compared with the other two sites, although no differences were apparent in fish assemblage structure between the pocket-beach and reference sites. These results suggested that the presence of headlands had marked effects on the surf-zone fish assemblage structure in the study area.     

卵巢运输保存温度和时间对野生梅花鹿卵母细胞体外成熟的影响

以屠宰日本北海道野生梅花鹿(Cervus nippon Temminck)卵巢为材料,研究了卵巢不同保存温度(20～25 ℃,10～15 ℃)和时间(12 h,24 h)及卵母细胞周围的卵丘细胞层对卵母细胞体外成熟的影响.结果表明,卵巢在20～25 ℃下保存12 h,卵母细胞成熟率为77%,无变形卵子出现,但其保存时间延长到24 h时,卵母细胞成熟率降至35%,变形率高达62%;而在10～15 ℃下保存12 h,卵母细胞成熟率为45%,卵母细胞变形率为18%,但10～15 ℃保存24 h与20～25 ℃保存24 h相比,卵母细胞变形率却很低(35%,62%)(P<0.05).周围卵丘细胞层3层以上和少于3层的卵母细胞中,48%～53%的受精卵都能正常地卵裂,但前者获得了13%的囊胚率,后者未发育至囊胚(P<0.05).     

Long-term observations of the vertical distributions of mineral elements and phosphorus dynamics in sediments in a shallow eutrophic lake in Japan

Purpose

To explore the mechanisms in the deposition and release of phosphorus (P) in the sediment of a shallow eutrophic lake using preserved samples, we investigated the vertical and temporal changes in P, manganese (Mn), sulfur (S), iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) in the sediment samples and the phosphate in the sediment pore water samples over a period of 6 years.

Materials and methods

The upper 15 cm of sediment from Lake Kasumigaura in Japan was collected monthly from 2003 to 2008 from the center of the lake. Sediment cores were divided into seven depth segments and were acid-digested for an elemental analysis via inductively coupled plasma atomic emission spectroscopy. Phosphate concentrations of the sediment pore water were determined using the molybdenum blue method. A multiple regression analysis was conducted by setting the P content as the response variable and Mn, S, Fe, Al, Ca, and Mg as explanatory variables.

Results and discussion

The results of the multiple regression analysis demonstrated that P co-precipitates with Fe and Al oxides and accumulates on the sediment surface. The vertical distributions of Mn and S suggest that Mn reduction occurs within the 0–1-cm-depth layer of the sediment and that iron sulfide is actively formed in the 6–10-cm-depth layer of the sediment. These findings imply that the layer in which ferric oxides are reduced to ferrous ions is present near the 1–6-cm-depth layer of the sediment. This layer corresponds to the layer in which the maximum phosphate concentration of the sediment pore water often occurred (the 2–6-cm-depth layer). These results indicate that vertical distributions of mineral elements are useful for assessing P dynamics in sediments.

Conclusions

The lake sediments record the dynamics of P in the sediment. Our analytical approach using long-term observation data demonstrated that the accumulation and release of P associated with a change in the redox state can be assessed based on the vertical distributions of mineral elements in the lake sediments.