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.     

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.     

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.     

The trophic cascade from fish to benthic algae: manipulation of habitat heterogeneity and disturbance in experimental flow-through pools

To investigate the effects of environmental change on the trophic cascade from fish to benthic algae, two 26-day experiments were conducted in outdoor flow-through pools. Habitat heterogeneity was manipulated by filling grooves under tiles with wood. Disturbance was simulated by removing invertebrates and benthic algae from tiles with a stainless steel brush 10 days before the end of the experiment. Benthic invertebrates and algae rapidly colonized the pools. Japanese dace Tribolodon hakonensis that had been introduced as a top predator fed predominantly on ephemeropteran nymphs, chironomid larvae, trichopteran larvae, and benthic algae. Predation and intimidation by the dace reduced the number of ephemeropteran nymphs and lowered the percentage of invertebrates on the upper surfaces and sides of the tiles. Consequently, dace increased the algal biomass through a trophic cascade. When dace were present, a disturbance did not reduce the numbers of invertebrates at the end of the experiment, probably because most invertebrates recolonized the tiles and new invertebrates rapidly colonized the pools. The manipulation of habitat heterogeneity reduced the number of trichopteran larvae, but did not affect other invertebrates that used all surfaces of the tiles. Consequently, trophic cascades were not damped by these changes of habitat heterogeneity and disturbance.     

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.     

Off-flavor of red sea bream Pagrus major reared in recirculating aquaculture systems with low salinity is caused by 2-methylisoborneol

Fisheries Science - We detected an earthy/musty off-flavor in the flesh of red sea bream Pagrus major cultured under low saline water conditions using two types of recirculating aquaculture systems...     

Validation of daily increment formation in otoliths of immature and adult Japanese anchovy <Emphasis Type="Italic">Engraulis japonicus</Emphasis>

In order to validate daily increment formation in otoliths of immature and adult Japanese anchovy Engraulis japonicus, three rearing experiments using chemical marking of otoliths were conducted on adult anchovy in summer 2004 and immature anchovy in summer 2005 and in winter 2006. In the two experiments conducted in summer, the number of otolith microincrements between alizarin complexone (ALC) marks showed that microincrements were formed daily. In the summer 2005 experiment, immature anchovy under conditions of reduced daily food rations also showed daily microincrement formation. Average increment width was 0.9 μm in adults and 1.8–3.1 μm in immature anchovy. In contrast, no clear increments were observed between ALC marks on the otoliths from the experiment in winter 2006, and scanning electron microscope (SEM) observations failed to confirm clear increment formation. We consider that low water temperatures (<13–14°C) restricted otolith growth and lowered the contrast between the discontinuous and the incremental zones of the otolith increments. For age estimation of Japanese anchovy, clear increments wider than about 1 μm in the otolith can be regarded as daily increments. However, daily age estimation of immature and adult anchovy that experience low water temperatures in winter may be difficult due to the obscurity of the increments.     

Mitigating sea turtle by-catch in coastal passive net fisheries

There is growing evidence that small-scale, coastal, passive net fisheries may be the largest single threat to some sea turtle populations. We review assessments of turtle interactions in these fisheries, and experiments on gear-technology approaches (modifying gear designs, materials and fishing methods) to mitigate turtle by-catch, available from a small number of studies and fisheries. Additional assessments are needed to improve the limited understanding of the relative degree of risk coastal net fisheries pose to turtle populations, to prioritize limited conservation resources and identify suitable mitigation opportunities. Whether gear technology provides effective and commercially viable solutions, alone or in combination with other approaches, is not well-understood. Fishery-specific assessments and trials are needed, as differences between fisheries, including in gear designs; turtle and target species, sizes and abundance; socioeconomic context; and practicality affect efficacy and suitability of by-catch mitigation methods. Promising gear-technology approaches for gillnets and trammel nets include: increasing gear visibility to turtles but not target species, through illumination and line materials; reducing net vertical height; increasing tiedown length or eliminating tiedowns; incorporating shark-shaped silhouettes; and modifying float characteristics, the number of floats or eliminating floats. Promising gear-technology approaches for pound nets and other trap gear include: replacing mesh with ropes in the upper portion of leaders; incorporating a turtle releasing device into traps; modifying the shape of the trap roof to direct turtles towards the location of an escapement device; using an open trap; and incorporating a device to prevent sea turtle entrance into traps.