Effect of an Introduced Phytoene Synthase Gene Expression on Carotenoid Biosynthesis in the Marine Diatom Phaeodactylum tricornutum

Carotenoids exert beneficial effects on human health through their excellent antioxidant activity. To increase carotenoid productivity in the marine Pennales Phaeodactylum tricornutum, we genetically engineered the phytoene synthase gene (psy) to improve expression because RNA-sequencing analysis has suggested that the expression level of psy is lower than other enzyme-encoding genes that are involved in the carotenoid biosynthetic pathway. We isolated psy from P. tricornutum, and this gene was fused with the enhanced green fluorescent protein gene to detect psy expression. After transformation using the microparticle bombardment technique, we obtained several P. tricornutum transformants and confirmed psy expression in their plastids. We investigated the amounts of PSY mRNA and carotenoids, such as fucoxanthin and β-carotene, at different growth phases. The introduction of psy increased the fucoxanthin content of a transformants by approximately 1.45-fold relative to the levels in the wild-type diatom. However, some transformants failed to show a significant increase in the carotenoid content relative to that of the wild-type diatom. We also found that the amount of PSY mRNA at log phase might contribute to the increase in carotenoids in the transformants at stationary phase.     

Comparison of factors affecting recruitment variability of walleye pollock Theragra chalcogramma in the Pacific Ocean and the Sea of Japan off northern Japan

The Japanese Pacific stock (JPS) and the northern Japan Sea stock (JSS) of walleye pollock Theragra chalcogramma are mainly distributed in the Pacific Ocean and the Sea of Japan off northern Japan, respectively. This paper summarizes and compares the factors affecting the recruitment variability of these two stocks. Spawning season is from December to March for both stocks. JPS recruitment has a positive relationship with the water temperature in January and February, whereas that of JSS has a negative relationship with the water temperature in January, February, and April. One possible reason for this is that pollock larvae have an optimum growth temperature of approximately 5 °C in the field. Drift of early life stages also appears to be an important influence on the recruitment of both stocks. Because the current generated by the northwest wind carries eggs of JPS into the main larval nursery ground, JPS recruitment is enhanced in years when the northwest wind is predominant in February. On the other hand, early life stages of JSS are transported into the nursery ground by the Tsushima Warm Current. However, this current also carries early life stages into the Sea of Okhotsk and offshore, resulting in poor JSS recruitment in years when this current is strong in March. In contrast to JPS, the recruitment of which is significantly impacted by cannibalism, young pollock have not been found in the stomachs of adult JSS. Warm temperatures in the Sea of Japan seem to induce the separation of young and adult pollock, and the shape of the stock–recruitment relationship also suggests that cannibalism is not important for JSS. Based on this knowledge, and on the hatch date distributions of larvae and juveniles, we propose mechanisms that can explain the recruitment fluctuations for JPS and JSS pollock.     

Eye structure and function in the giant freshwater prawn Macrobrachium rosenbergii

We used histological and electroretinogram methods to investigate eye structure and function in Macrobrachium rosenbergii. M. rosenbergii was demonstrated to have superposition compound eyes with a clear zone. Rhabdom volume dramatically increased only under dark-adapted conditions at night. The eyes were assumed to be dark adapted after about 50 min under dark conditions, and to be light adapted after about 4 min under light conditions during the day. The mean angle between receptor units was 1.75°. The slope of the visual sensitivity (V/log I) curve of M. rosenbergii was 0.40 and the K value (stimulus irradiance eliciting half of the maximum response) was 16.1 log photons cm^?2 s^?1. The mean dynamic range was 4.06, ranging from 13.91 to 17.97 log photons cm^?2 s^?1. The response latency was 19.6 ± 7.5 ms (mean ± SD). Analysis of the visual spectral sensitivity of dark-adapted specimens indicated that the sensitivity maximum was centered at a wavelength of 563 nm in the yellow–green region of the spectrum. The critical flicker fusion frequency increased as stimulus irradiance increased, up to a maximum of 44.3 Hz at almost the same stimulus irradiance of the K value.     

Molecular cloning and expression profiling of procollagen α1 (I) of cultured Pacific bluefin tuna

Type I collagen is widely distributed in most organs in teleosts. It plays a role not only in intercellular adhesion, but also in molecular signaling. In this study, Pacific bluefin tuna (PBT) procollagen α1 (I) cDNA was cloned and characterized. The nine fragments of a procollagen α1 (I) chain cDNA clone were prepared and spliced together to create the complete coding region. The resulting amino acid sequence was homologous with that of other teleosts. The mRNA expression profile of PBT procollagen α1 (I) in various tissues and the phylogenetic analysis with other vertebrate procollagen α1 (I) chains suggest that PBT procollagen α1 (I) could be a precursor form of the PBT type I collagen α1 chain. In addition, its level of expression in PBT larvae and early juveniles gradually increased with somatic growth. This increase was related to the standard length, wet body weight, and protein content of each individual fish. Therefore, the expression profile of procollagen α1 (I) may be a useful indicator for somatic growth in fish larvae and juveniles.     

Experimental analysis on the relationship between the population density of ayu Plecoglossus altivelis altivelis and fishery catch by “Tomozuri” angling

To investigate the relationship between the population density of ayu and the survival rate, number of ayu caught by “Tomozuri” angling and total fishery catch, ayu were introduced into experimental ponds with currents at densities of 1.1–6.1/m² in 2011 and 2012. After stocking in May, fishing was conducted from early July to late August or early September. The proportion of dead ayu in each pond was less than 20 % through the experiment and was not correlated with the initial density of ayu in either year. The growth rates of ayu that were fished and that remained in ponds to the end of the experiment were negatively correlated with the initial density. However, the number and catch of ayu fished by Tomozuri peaked at an initial density of 2.6–4.7/m². Medium- and large-sized ayu heavier than 30 and 50 g, respectively, caught by fishing peaked at initial densities of 2.6/m² and 2.1–2.6/m². These results suggest that the traditional criterion on the stock density of ayu, 0.6–0.7/m², is too low from the viewpoint of Tomozuri angling, and recent stock densities used in many prefectures, 0.5–2.0/m², are not sufficient.     

Interannual changes in the timing of walleye pollock spawning migration and their impacts on the gillnet fishery in the southwestern Pacific coast of Hokkaido,Donan area,Japan

The southwestern Pacific coast of Hokkaido is the main spawning ground for the Japanese Pacific stock of walleye pollock Theragra chalcogramma. A commercial gillnet fishery targeting spawning adult pollock in this area mainly operates from October to January to coincide with the migration of adult pollock from the feeding ground. Given the results of acoustic surveys, and changes in the proportion of the monthly total catch that was monthly walleye pollock caught by the commercial gillnet fishery, it is thought that the timing of walleye pollock spawning migration to the Donan area varies among years and that the pollock catch of the gillnet fishery clearly reflects changes in pollock abundance in this area. A time series of interannual variability in catch data from 1980 to 2005 suggested that adult pollock migrated and concentrated on their spawning ground later in the 1980s and after 2000 than in the 1990s. Such decadal-scale shifts are presumably caused by climatic changes (e.g., in water temperature) in the Oyashio region. These shifts affect the gillnet fishery through differences in monthly unit prices of pollock and changes in the formation of fishing grounds. These scientific findings can aid the establishment of rules for more efficient walleye pollock resource management under the total allowable catch system.     

Gonadal maturation and spawning migration of stocked female barfin flounder Verasper moseri off the Pacific coast of northern Japan

Commercial catches of barfin flounder Verasper moseri, an important target flatfish for stock enhancement programs in northern Japan, have recovered remarkably since the large-scale release of seedlings from Hokkaido in 2006. However, their reproductive ecology remains unclear. Our study of 2008–2012 investigated seasonal changes in the maturity of stocked female barfin flounder (n = 4,123) off the Pacific coast from Hokkaido to Tohoku (35.7°–43.4°N). Histological observation of ovaries revealed that fish undergoing vitellogenesis were observed mainly off Hokkaido and partially off northern Tohoku during August–January (40.2°–43.4°N). However, fully matured or spawning fish were not found near those areas. They were observed only in southern Tohoku. Ongoing spawning was observed off southernmost Tohoku (35.8°–37.5°N around 300 m depth) from early February through late April, when commercial landings had decreased drastically off Hokkaido. Spent fish were caught only rarely off southern Tohoku, but were observed frequently off Hokkaido during April–June. These results demonstrate that spawning grounds form at the upper continental slope off southernmost Tohoku during February–April. Relations between maturation traits and seasonal landings strongly suggest that female barfin flounder repeatedly migrate more than 700 km from feeding grounds off Hokkaido to spawning grounds off southern Tohoku.     

Bacterial leaf spot of hemp caused by Xanthomonas campestris pv. cannabis in Japan

Bacterial leaf spot disease of hemp was observed in Tochigi Prefecture, Japan in 1982 and characterized by necrotic lesions ca. 1–2 mm diameter on leaves with a yellow halo 2–3 mm wide. In this report, we describe the pathological, physiological and genetic properties of the causal bacterium. Our results indicated that this bacterium is identical with Xanthomonas campestris pv. cannabis reported in Romania.     

Avian colibacillosis caused by an intestinal pathogenic Escherichia coli isolate from calf diarrhea

An intestinal pathogenic Escherichia coli isolate from calf diarrhea, containing the iutA, f17A, afa-8D, and cnf2 genes, was able to cause avian colibacillosis after experimental infection in chickens. Intra-tracheal inoculation and spray of this strain caused 10% of mortality and gross lesions, including airsacculitis, pericarditis, and perihepatitis. These results suggest that some bovine pathogenic E. coli can cause extra-intestinal infections in other animal species.