Genetic characterization of ayu Plecoglossus aliivelis aliivelis occurred in Nakaumi Lagoon

Ayu Plecoglossus altivelis altivelis is a common fish that is composed by two major forms, amphidrDmOuS and landlocked forms, based on itsannual1ife history. Althoughrecent decline in the reserves of amphidromous stocks in rivers has prompted frequent transplantations from landlocked stocks, a low survival rate of larvae of the landlocked fbm occllrS during periods of high water temperature in seawater. In brackish water environment, however, non-native landlocked form may survive and show sympatric distribution with mother populations. This study was conducted to verifythe genetic status of ayll 0cclmed in Nakaumi Lagoon, which is the second largest brackish lake in Japan. Nucleotide sequence polymoIPhism of the first 300 bp of themitochondrial DNA control region Was analyzed for 30 individuals including each 15 Specimens collected from 2 locales ofNakaumi Lagoon in May 2009, along with each 15 reference specimens oftheamphidromous and landlocked stocks. Comparatively high1evels of nucleotide substitution were observedwith 35 polymoIPhic sites from Nakatlm population and 40 sites from the amphidromous stock, as contrasted with24 sites from the landlocked stock. Based on nucleotide sequences at 5 hypervariable sites, 2 haplotypes occured in only the amphidromousstock were obtained at a high frequency in Nakaumi Population These results suggest that the amphidromous form forms the majority of Nakaum population.Article信州大学山地水環境教育研究センター研究報告 6: 125-132(2010)departmental bulletin pape

Environmental management and restoration under unified risk and uncertainty using robustified dynamic Orlicz risk

Environmental management and restoration should be designed such that the risk and uncertainty owing to nonlinear stochastic systems can be successfully addressed. We apply the robustified dynamic Orlicz risk to the modeling and analysis of environmental management and restoration to consider both the risk and uncertainty within a unified theory. We focus on the control of a jump-driven hybrid stochastic system that represents macrophyte dynamics. The dynamic programming equation based on the Orlicz risk is first obtained heuristically, from which the associated Hamilton-Jacobi-Bellman (HJB) equation is derived. In the proposed Orlicz risk, the risk aversion of the decision-maker is represented by a power coefficient that resembles a certainty equivalence, whereas the uncertainty aversion is represented by the Kullback-Leibler divergence, in which the risk and uncertainty are handled consistently and separately. The HJB equation includes a new state-dependent discount factor that arises from the uncertainty aversion, which leads to a unique, nonlinear, and nonlocal term. The link between the proposed and classical stochastic control problems is discussed with a focus on control-dependent discount rates. We propose a finite difference method for computing the HJB equation. Finally, the proposed model is applied to an optimal harvesting problem for macrophytes in a brackish lake that contains both growing and drifting populations

Population genetic structure ofYamato-sllijimi clam in Lake Sbinji, Japan

Yamato-shijimiclam Corbicula japonica is the best-known bivalve inhabiting ln brackish estuaries and lakes around Japan and one of the most commercially important species in inland fisheries. Althoughthe amotmt of C japonica from Lake Shinji has accotmted for the large part of the domestic catch, itsamolmt has dramatically fallen in recent years･ This study was conducted to verifythe genetic structtue and reproduction mechanism of C･ japonica, both of which are essential to its stock management in Lake Shinji. Weanalyzed sequence polymorphism of the 588 bp portion ofthemitochondrial DNA cytochrome oxidase subunit I (Col) gene to determinethe population genetic structure of C･ japonica in Lake Shinji･Among a total of 177 C･ japonica specimens collected from 4 colonies, 37 haplotypes were obtained, and 2 major haplotypes were apparent withrelatively highabtmdance in all colonies･ Well correspondingmismatch distributions along the Col gene were determined for the data sets of the individual colonies, and the pairwise population estimates FsT among the individual colonies were also generally low, Such small genetic differentiation of C japonica is derived kom highgeneflow in Lake Shinji, and this could be caused by a lake-wide dispersion of its larvae mediated by the water movements･Article信州大学山地水環境教育研究センター研究報告 6: 115-124(2010)departmental bulletin pape

Relationship between gyrA Mutations and Quinolone Resistance in Flavobacterium psychrophilum Isolates

Flavobacterium psychrophilum is the causative agent of the fish diseases called bacterial cold-water disease and rainbow trout fry syndrome. It has been reported that some isolates of F. psychrophilum are resistant to quinolones; however, the mechanism of this quinolone resistance has been unexplained. In this study, we examined the quinolone susceptibility patterns of 27 F. psychrophilum strains isolated in Japan and the United States. Out of 27 isolates, 14 were resistant to both nalidixic acid (NA) and oxolinic acid (OXA), and the others were susceptible to NA and OXA. When amino acid sequences deduced from gyrA nucleotide sequences of all isolates tested were analyzed, two amino acid substitutions (a threonine residue replaced by an alanine or isoleucine residue in position 83 of GyrA [Escherichia coli numbering] and an aspartic acid residue replaced by a tyrosine residue in position 87) were observed in the 14 quinolone-resistant isolates. These results strongly suggest that, as in other gram-negative bacteria, DNA gyrase is an important target for quinolones in F. psychrophilum